Placenta Previa and Prior Cesarean

Illustration of Complete Previa, with the placenta at
the bottom of the uterus, between baby and the cervix.
Image by Sigrid de Rooij,Wikimedia Commons

As a follow-up to Cesarean Awareness Month last month, we are talking about late complications from cesareans.

A cesarean section is surgery, and thus entails the usual immediate risks associated with surgery, including infection, hemorrhage, anesthesia problems, blood clots, and accidental damage to surrounding tissues.  These alone are substantial enough to warrant concern with the current high cesarean rate.

However, what many people don't realize is that a cesarean also has downstream health implications, long after the cesarean is over, particularly in women who have further pregnancies after the cesarean(s).

In particular, the risk for abnormal placentation rises with each successive cesarean. And abnormal placentation has a high risk for poor outcomes.

Today we are going to discuss the most common of the complications, Placenta Previa.

Placenta Previa

Placenta Previa is the term for a placenta that lies over or near the cervix at the bottom of the uterus instead of on the top or sides of the uterus (see diagram). It is a significant complication in pregnancy. The number of previas has increased in recent years in tandem with the rising cesarean rate and other factors.

Placentas usually implant higher in the uterus, either near the top (fundal), or on the sides (anterior/front side, posterior/back side).

A low-lying placenta is a problem because as the pregnancy progresses, the lower uterine segment (LUS) expands and develops and the cervix begins to thin. This can cause a part of the placenta to shear off (abrupt) and begin to bleed.

This partial abruption of the placenta is often minor at first, but can become major later on, endangering both baby and mother. In addition, in some previas the placenta can block the cervix, making vaginal birth dangerous.

Symptoms of previa include painless bleeding after 24 weeks or so of gestation. The most typical presentation of bleeding is around 32 weeks or so, although some previas never experience bleeding episodes at all. Elevated maternal alpha fetoprotein levels during prenatal testing may also be a sign of a possible previa.

Any woman who experiences bleeding episodes after about 20 weeks should be evaluated by a care provider.

If you are diagnosed with Placenta Previa, it is important for you to learn more about the condition so you can become a partner in your own care decisions.  In addition, it is very helpful to reach out to a support group so that you can get support as you deal with the previa experience.

If You Are Diagnosed with Placenta Previa

A transvaginal ultrasound is by far the best method of checking placental placement if previa is suspected. Research shows that a number of previas suspected with abdominal ultrasound are able to be ruled out with transvaginal ultrasound.

There are four grades of severity in previas:

• Type One - placenta is near but not touching mouth of cervix (low-lying placenta)
• Type Two - placenta reaches mouth of the cervix but doesn't cover it (marginal previa)
• Type Three - placenta partially covers the mouth of the cervix (partial previa)
• Type Four - placenta completely overlays the mouth of the cervix (complete or total previa)

It's important to note that a placenta can look low-lying in early pregnancy but "move up" in the uterus as the uterus grows and develops during pregnancy.

Most borderline previas in early or mid-pregnancy completely resolve by the end of pregnancy, or move up enough that the risk is lessened. 

Thus, it's important not to panic if you are told you have a previa early in pregnancy.  Most of the time it just bears watching and will resolve.

However, some never do resolve. This is called a persistent previa. A complete previa where the mouth of the cervix (the os) is completely covered is the most likely to persist until delivery, although it should be noted that some of these do resolve by term.

Posterior previas are less likely to resolve than anterior previas.  A prior cesarean has been shown to be a strong independent risk factor for a persistent previa. Complete previas that are very symmetrically over the os are also likely to persist to term.

All women with significant placenta previa should be evaluated for the possibility of Placenta Accreta (an abnormally adherent placenta) or Vasa Previa (where fetal blood vessels are situated in the membranes over the cervix without the protection of the cord or placenta). Women with a history of cesareans, D&Cs, or in-vitro fertilization should be particularly evaluated for these conditions.

Most of the time, previas completely resolve by term and labor proceeds normally. If the previa is still there by 35 weeks but is minor (2 cm or more from the os), vaginal birth is quite possible, and has a good success rate.

Some providers will also allow women with previas that are 1-2 cm from the os to try for vaginal birth, whereas others feel this is too risky. Even with a vaginal delivery, however, the mother with a marginal or low-lying placenta still needs to be watched carefully for postpartum hemorrhage.

If the placenta is very near or overlays the os at all by 35 weeks, then delivery needs to be by cesarean in order to prevent hemorrhage when the cervix begins to thin and dilate.  Although regional anesthesia (epidural or spinal) can be used, many providers prefer general anesthesia because of the unpredictability of surgery length and the potential for emotional trauma if complications occur.  Some providers start with regional anesthesia to minimize fetal exposure to drugs, then convert to general anesthesia after the baby is delivered.

A cesarean for an anterior previa is a difficult surgery with the potential for major hemorrhage because it can mean cutting through the placenta itself in order to get to the baby.  Many OBs decide to avoid the placenta altogether by doing a high vertical or transverse fundal incision instead, because this may lessen bleeding and make it easier if a hysterectomy is needed. However, it can also mean a more difficult recovery. Discuss the pros and cons of each choice with your provider ahead of time.

Postpartum, previa mothers need to be monitored for hemorrhage, infection, and anemia. In some mothers who experience very severe hemorrhage, milk supplies are impaired and the pituitary gland can be damaged (Sheehan's Syndrome).  Hypothyroidism and adrenal fatigue issues can occur secondary to Sheehan's Syndrome and should be monitored for carefully for years, as symptoms may not become clear until long after the birth.

Postpartum, some mothers have a tough time coping emotionally or may not feel they have enough emotional support after a difficult experience. Many find their experiences dismissed or shrugged off as if a healthy baby is the only thing that matters.  It's important to know that emotional support is available through Sidelines, ICAN, Solace for Mothers, and many other organizations.

Risks Associated with Placenta Previa

Although many women with previas have reasonably good outcomes, previas are associated with an increased risk of a number of complications.

The risk of hemorrhage is the most important of these complications. One study found that nearly 60% of women with previa experienced a significant hemorrhage, and nearly 12% required a blood transfusion.

However, a lot depends on how severe the previa is and whether it detaches normally. Women with low-lying previas (type 1), for example, had only a 7.6% rate of hemorrhage.  As you might expect, women with complete previas tend to have worse outcomes than those with more marginal previas, as would those who also have an accreta (abnormally adherent placenta).

Because of the risk of hemorrhage, it's important to have adequate blood products on hand at a previa birth. Women with a possible previa should try to boost their iron status during pregnancy in order to minimize the impact of significant blood loss during the birth, should it occur.

Women with high hemoglobin levels may want to look into donating and banking their own blood ahead of time in case a transfusion is needed.  They may also want to inquire about the possibility of recycling and re-using any of their blood lost during the cesarean.

In addition to bleeding, the risk for postpartum infection may be higher in women with previas. In some cases, hemorrhage or infection makes a hysterectomy necessary, thus ending the woman's fertility forever. Some sources even recommend a prophylactic cesarean hysterectomy as a precaution, especially if an accreta is also suspected. Multiple prior cesareans increase the chance that a hysterectomy may be needed.

Because the placenta (the source of oxygen and food for the baby) often begins to pull away from the lower uterine segment as pregnancy progresses, the baby in a previa pregnancy is endangered.  It often must be born prematurely and as a result, may need care in the Neonatal Intensive Care Unit (NICU).

Some studies (but not all) show an increase in the rate of Intrauterine Growth Retardation (IUGR) in babies of previa pregnancies. And the rate of perinatal mortality is three to four times higher in a previa pregnancy.  However, many babies of a previa pregnancy do just fine.

If you are diagnosed with a previa, complete pelvic rest will be prescribed (no sex, nothing in the vagina, no pelvic exams, etc.).  Bed rest is common, or at least restrictions from vigorous activity.

Some women with significant bleeding episodes are hospitalized until the baby is delivered, whereas others can be monitored as outpatients. Medicine to prevent premature labor and steroids to mature the baby's lungs early may be given if early delivery looks likely.

The optimal delivery time for women with a complete previa is difficult to know. Providers seek to find a balance between the risk of a severe hemorrhage in the mother versus increased problems in the baby from prematurity. A substantial number of complete previas are delivered before 34 weeks because of significant bleeding episodes during pregnancy. However, most previas are able to go longer.

A recent review recommended a delivery around 36-37 weeks in women with complete previa who are not experiencing severe bleeding episodes. Another review recommended delivery at 36 weeks (2 days after administration of steroids for the baby's lungs). However, RCOG (the British version of ACOG) states that women with uncomplicated cases of placenta previa can wait until 38-39 weeks. A lot depends on the circumstances of each individual case and the practices of attending physicians.

Because some studies have found an increased risk for perinatal mortality in deliveries after 37 weeks, the reality in most hospitals these days is that women with complete previas are usually delivered before term and must therefore deal with prematurity issues.

With significant previas, it is important to be in a hospital that specializes in high-risk deliveries so that a specialized team of surgeons, anesthesiologists, and neonatologists are nearby at all times, as well as the capability for major blood transfusions.  The mother needs to be ready for the possibility that a hysterectomy may become necessary.

Although most women with previas will have reasonably good outcomes, previa is definitely a high-risk condition that deserves careful monitoring and a thorough plan for optimizing outcomes.

Placenta Previa and Prior Cesareans

So why is a woman with a prior cesarean at greater risk for a previa?

The answer seems to be related to the damage done to the uterus from the surgery.

Placenta Previa develops when the uterine lining has been damaged somehow and the fertilized egg implants near this damaged area.

As one resource says:

It is hypothesized to be related to abnormal vascularisation of the endometrium caused by scarring or atrophy from previous trauma, surgery, or infection. These factors may reduce differential growth of lower segment, resulting in less upward shift in placental position as pregnancy advances.

Risk factors for developing Placenta Previa include the mother's age, prior cesareans, smoking or drug use, high number of prior pregnancies, closely-spaced pregnancies, prior uterine surgery, pregnancy with multiples, congenital anomalies (birth defects), assisted reproduction technology (assisted fertilization), endometriosis, and prior D&C procedures.

Although multiple risk factors are at work with Placenta Previa, it is clear that cesareans are one of the strongest risk factors.

Even only one prior cesarean raises the risk for previa significantly.  One large study found:

The rate of placenta previa at second birth for women with vaginal first births was 4.4 per 1000 births, compared to 8.7 per 1000 births for women with CS at first birth.

Another study (Getahun 2006) found that the incidence of previa was higher (0.63%) in women whose first birth was by cesarean than in women whose first birth was vaginal (0.38%).

The risk for previa is even higher with multiple prior cesareans.  As Getahun 2006 concluded:

There is a dose-response pattern in the risk of previa, with increasing number of prior cesarean deliveries.

A research review (Ananth 1997) looked at four studies that were able to stratify the relative risk of previa by number of prior cesareans. The relative risks were:

• 4.5 for one prior cesarean
• 7.4 for two prior cesareans
• 6.5 for three prior cesareans
• 44.9 for four or more prior cesareans

But what does that mean in actual numerical risk?  Most studies only show relative risk, but a few studies do have some hard numbers by number of prior cesareans.  For example, Clark (1985) found the following incidence of previa:

• unscarred uterus = 0.26% previa
• 1 c/s = 0.65% previa
• 2 c/s = 1.8% previa
• 3 c/s = 3.0% previa
• 4+c/s = 10.0% previa

Of course, exact numerical risk varies from study to study.  To 1995 found a previa incidence of:

• 0.75% in women with no prior cesareans
• 1.22% in women with one prior cesarean
• 2.11% in women with two or more prior cesareans

In Juntunen 2004, the previa rate was 0.5% in the general population, but was 5.4% among with four or more prior cesareans. Obviously, the exact rate depends on the study, but the trend is clear.  The more cesareans you have had, the greater your risk for developing previa. 

Although parity (number of prior pregnancies) and number of prior cesareans are both risk factors for previa, they interact to increase the risk even more. In Gilliam 2002, a woman who had 4+ pregnancies but only one cesarean had 1.72x the risk for previa, but a woman who had 4+ pregnancies and 4+ cesareans had 8.76x the risk for previa.

And when a previa is present, a history of multiple prior cesareans increases the risk for poor maternal outcome significantly, including transfusion, hysterectomy, operative injury, coagulopathy, venous thromboembolism, pulmonary edema, or death.

This points out the importance of VBAC access and avoiding multiple repeat cesareans whenever possible.

Unfortunately, that's the exact opposite of the trend in obstetrics these days.

My "Previa" Story

As many readers of this blog know, I had two cesareans and then two VBACs with my children.  What I haven't shared is that I had a previa scare with my third.

In that pregnancy, my placenta implanted in the front of the uterus (anterior), down low and near the scar, although we didn't know it at first. I chose not to have an early ultrasound, so it was not until my ultrasound near the end of the second trimester that we discovered that my placenta was anterior.

Anterior placentas are notorious for making it hard to hear the baby's heartbeat at first. That led to one midwife telling me (in a very callous way) that I had obviously miscarried the pregnancy. Fortunately, a different midwife was later able to find the baby's heartbeat and let me know that the pregnancy was still viable.  But it was an angst-filled time until we were able to know that for sure.

If we'd had an early ultrasound, I might have been able to confirm more easily that the pregnancy was still there despite the anterior placenta blocking the sound of the heartbeat, but we also would have experienced a big scare about placenta previa. That anterior placenta's location over my scars would have caused a lot of worry and panic to us all. By delaying the ultrasound till later, the placenta had "moved up" and we knew that neither previa nor accreta was present.

Although it's always a woman's choice whether or not to have prenatal testing, it may be prudent to consider at least one ultrasound to check placentation in women with a history of cesareans or other uterine instrumentation.

Prenatal testing always comes with pros and cons, but remember, some previas and accretas are not symptomatic before birth, and outcomes are improved if these conditions are discovered before birth.  Therefore, the more cesareans you have had, the more you might want to consider an ultrasound for placental placement. Such testing is never compulsory, mind, but it is probably strongly worth considering in this situation.

However, too many women with prior cesareans are subjected to unnecessary worry and additional testing by early ultrasounds that show a low placenta near the scar. Research shows that 90-95% of previas diagnosed by the second trimester will resolve by term.

So although an ultrasound to check placental placement is a prudent thing to consider in women with prior cesareans, women might want to consider waiting until later in pregnancy to do so unless there is bleeding or other issues that necessitate earlier testing.

Summary

Cesareans are not good or bad in and of themselves. Sometimes they can be life-saving, sometimes they are prudent, sometimes they are a choice. But the cesarean rate in many areas of the world is quite high, and this comes with consequences.

One of the major public health implications of a high cesarean rate is placental complications in subsequent pregnancies after the cesarean. Of these placental issues, Placenta Previa is the most common.

The incidence of Placenta Previa is generally cited in most sources these days as about 1 in 200 to 1 in 250 over the whole pregnant population (0.4 - 0.5%).

However, some earlier studies cite an incidence of between 0.2% to 0.5%. One meta-analysis from the 1990s states:

An examination for trends over time in the incidence of placenta previa revealed that the incidence of this disorder was almost similar until the mid-1980s (1966 to 1974: incidence was 0.36%; 1975 to 1984, 0.37%), but the incidence was 0.48% among studies conducted between 1985 and 1995.

Some studies now place the incidence between 0.5% and 1.5%. However, the prevalence varies greatly from study to study and area to area.  Much depends on the characteristics of the population being studied.

An increase in older mothers, an increased use of D&Cs, increased fertility treatments, and the huge increase in cesarean rates may explain the increased rate of previas in recent years. Yet it's important to note that of these influences, the high cesarean rate may be the most modifiable risk factor. 

The main risk of previa is significant bleeding issues with the placenta as the pregnancy progresses, and especially when the cervix begins to thin and dilate. Previa is associated with a significant risk for severe hemorrhage in the mother and may necessitate blood transfusions or hysterectomy. Although rare, sometimes the mother even dies, especially in third world countries.

In the baby, previa is associated with increased rates of prematurity, respiratory distress, NICU care, and congenital anomalies. The perinatal mortality rate is significantly higher in pregnancies complicated by previa.

When previa occurs, the more prior cesareans a woman has had, the worse her chances for a "morbidly adherent" placenta (an accreta), as well as for major maternal morbidity (hemorrhage, transfusions, blood clot, pulmonary edema, operative injury, hysterectomy, or death).

And the risk doesn't end there. A woman is at higher risk for another previa in future pregnancies after a first previa pregnancy, as well as for another premature birth (even with subsequent normal placentation).

In other words, lower the rate of unnecessary primary and repeat cesareans, and you may prevent quite a number of maternal hysterectomies, severe hemorrhages, premature babies, and perinatal deaths from previa down the road.

Clearly, Placenta Previa is a major potential complication of pregnancies after a prior cesarean. As the authors of one meta-analysis on previa and prior cesareans concluded:

This study provides yet another reason for reducing the rate of primary cesarean delivery and for advocating vaginal birth for women with prior cesarean delivery.

Care providers and hospitals, are you listening?


References

General Information on Placenta Previa

• http://www.nlm.nih.gov/medlineplus/ency/article/000900.htm
• http://www.ncbi.nlm.nih.gov/pubmed/17346497
• http://pregnancy.about.com/cs/placentaprevia/a/previa.htm
• http://www.patient.co.uk/doctor/placenta-praevia
• http://en.wikipedia.org/wiki/Placenta_praevia
• http://www.mayoclinic.com/health/placenta-previa/DS00588
• http://www.ncbi.nlm.nih.gov/pubmed/17346497
• http://www.obfocus.com/high-risk/placentaprevia.htm
• http://www.rcog.org.uk/files/rcog-corp/GTG27PlacentaPraeviaJanuary2011.pdf
• http://www.rcog.org.uk/womens-health/clinical-guidance/placenta-praevia-and-placenta-praevia-accreta-diagnosis-and-manageme
• http://americanpregnancy.org/pregnancycomplications/placentaprevia.html
• http://www.placentaprevia.org/

Resources

• Sidelines - support group for women with high-risk pregnancies, especially those on bedrest
• Coping with Bedrest - information from maternal-fetal medicine specialists about coping with bed rest proactively and staying sane
• Coping with Prematurity - links to organizations and books about dealing with preemies
• Miracle Babies - organization to support families with premature babies in the NICU
• International Cesarean Awareness Network (ICAN) - support for women who have experienced a cesarean or who will need a planned cesarean
• Solace For Mothers - support group for women who have experienced a traumatic birth
• www.tabs.org.nz – TABS (Trauma And Birth Stress support group)
• www.birthtraumaassociation.org.uk – info on PTSD after childbirth
• www.ptsdafterchildbirth.org – info on PTSD after childbirth
• www.emdria.org - Eye Movement Desensitization and Reprocessing International Association
• http://www.angelfire.com/moon2/jkluchar1995/my_emdr.html - information on the use of EMDR (Eye Movement Desensitization and Reprocessing) in treating PTSD
• http://health.groups.yahoo.com/group/ptsdafterchildbirth/ - support group for PTSD after birth
• http://www.mothering.com/community/forum/list/502 - forum to provide a place for healing spiritually, physically and mentally after birth as well as in preparation of birth or pregnancy

Placenta Previa Incidence Trends

Aust N Z J Obstet Gynaecol. 2012 Oct;52(5):483-6. doi: 10.1111/j.1479-828X.2012.01470.x. Epub 2012 Aug 2. Trends and recurrence of placenta praevia: a population-based study. Roberts CL, Algert CS, Warrendorf J, Olive EC, Morris JM, Ford JB. PMID: 22862285

We determined recent trends and recurrence rates of placenta praevia in 790,366 deliveries in NSW. From 2001 to 2009, the rate of placenta praevia increased by 26%, from 0. 69% to 0. 87% (trend P < 0.001). The placenta praevia recurrence rate in a second birth was 4.8%. Two-thirds of the increase in placenta praevia was accounted for by trends in known risk factors, and the unexplained portion may reflect changes in unidentified risk factors or in the threshold for placenta praevia diagnosis.

Placenta Previa Adverse Outcomes

Arch Gynecol Obstet. 2011 Jul;284(1):47-51. doi: 10.1007/s00404-010-1598-7. Epub 2010 Jul 22. Critical analysis of risk factors and outcome of placenta previa. Rosenberg T, Pariente G, Sergienko R, Wiznitzer A, Sheiner E. PMID: 20652281

...RESULTS: During the study period, there were 185,476 deliveries, of which, 0.42% were complicated with placenta previa. Using a multivariable analysis with backward elimination, the following risk factors were independently associated with placenta previa: infertility treatments (OR 1.97; 95% CI 1.45-2.66; P < 0.001), prior cesarean delivery (CD; OR 1.76; 95% CI 1.48-2.09; P < 0.001) and advanced maternal age (OR 1.08; 95% CI 1.07-1.09; P < 0.001). Placenta previa was significantly associated with adverse outcomes such as peripartum hysterectomy (5.3 vs. 0.04%; P < 0.001), previous episode of second trimester bleeding (3.9 vs. 0.05%; P < 0.001), blood transfusion (21.9 vs. 1.2%; P < 0.001), maternal sepsis (0.4 vs. 0.02%; P < 0.001), vasa previa (0.5 vs. 0.1%; P < 0.001), malpresentation (19.8 vs. 5.4%; P < 0.001), postpartum hemorrhage (1.4 vs. 0.5%; P = 0.001) and placenta accreta (3.0 vs. 1.3%; P < 0.001). Placenta previa was significantly associated with adverse perinatal outcomes such as higher rates of perinatal mortality (6.6 vs. 1.3%; P < 0.001), an Apgar score <7 after 1 and 5 min (25.3 vs. 5.9%; P < 0.001, and 7.1 vs. 2.6%, P < 0.001, respectively), congenital malformations (11.5 vs. 5.1%; P < 0.001) and intrauterine growth restriction (3.6 vs. 2.1%; P = 0.003). CONCLUSIONS: Infertility treatments, prior cesarean section, and advanced maternal age are independent risk factors for placenta previa. An increase in the incidence of these risk factors probably contributes to a rise in the number of pregnancies complicated with placenta previa and its association with adverse maternal and perinatal outcomes. Careful surveillance of these risk factors is recommended with timely delivery in order to reduce the associated complications.

Obstet Gynecol. 2007 Dec;110(6):1249-55. Pregnancy outcomes for women with placenta previa in relation to the number of prior cesarean deliveries. Grobman WA, Gersnoviez R, Landon MB, Spong CY, Leveno KJ, Rouse DJ, Varner MW, Moawad AH, Caritis SN, Harper M, Wapner RJ,Sorokin Y, Miodovnik M, Carpenter M, O'Sullivan MJ, Sibai BM, Langer O, Thorp JM, Ramin SM, Mercer BM; National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units (MFMU) Network. PMID: 18055717

...METHODS: Women with a placenta previa and a singleton gestation were identified in a concurrently collected database of cesarean deliveries performed at 19 academic centers during a 4-year period. Maternal and perinatal outcomes were analyzed after stratifying by the number of cesarean deliveries before the index pregnancy. RESULTS:...Multiple measures of maternal morbidity (eg, coagulopathy, hysterectomy, pulmonary edema) increased in frequency as the number of prior cesarean deliveries rose. Even one prior cesarean delivery was sufficient to increase the risk of an adverse maternal outcome (a composite of transfusion, hysterectomy, operative injury, coagulopathy, venous thromboembolism, pulmonary edema, or death) from 15% to 23%, which corresponded, in multivariable analysis, to an adjusted odds ratio of 1.9 (95% confidence interval 1.2-2.9)...CONCLUSION: Among women with a placenta previa, an increasing number of prior cesarean deliveries is associated with increasing maternal, but not perinatal, morbidity.

Am J Obstet Gynecol. 2003 May;188(5):1299-304. The effect of placenta previa on neonatal mortality: a population-based study in the United States, 1989 through 1997. Ananth CV, Smulian JC, Vintzileos AM. PMID: 12748502

...STUDY DESIGN: A retrospective cohort study was performed of live births in the United States (1989-1991 and 1995-1997) that used the national linked birth/infant death records from 22,368,235 singleton pregnancies...RESULTS: Placenta previa was recorded in 2.8 per 1000 live births (n = 61,711). Neonatal mortality rate was 10.7 with previa, compared with 2.5 per 1,000 among other pregnancies (relative risk, 4.3; 95% confidence interval, 4.0,4.8). At 28 to 36 weeks, babies born to women with placenta previa weighed, on average, 210 g lower than babies born to women without placenta previa (P <.001)...CONCLUSION: The risk of neonatal mortality was higher for babies born to women with placenta previa than for babies born to women without placenta previa who were delivered at > or =37 weeks of gestation. Pregnancies that are diagnosed with placenta previa must be monitored carefully, especially as they approach term.

Obstet Gynecol. 1999 Apr;93(4):541-4. Neonatal outcomes with placenta previa. Crane JM, van den Hof MC, Dodds L, Armson BA, Liston R. PMID: 10214830

...METHODS: This was a population-based, retrospective cohort study involving all singleton deliveries in Nova Scotia from 1988 to 1995...RESULTS: Among 92,983 pregnancies delivered during the study period, 305 cases of placenta previa were identified (0.33%). After controlling for potential confounders, neonatal complications significantly associated with placenta previa included major congenital anomalies (odds ratio [OR] 2.48), respiratory distress syndrome (OR 4.94), and anemia (OR 2.65). The perinatal mortality rate associated with placenta previa was 2.30% (compared with 0.78% in controls) and was explained by gestational age at delivery, occurrence of congenital anomalies, and maternal age. Although there was a higher rate of preterm births in the placenta previa group (46.56% versus 7.27%), there was no difference in birth weights between groups after controlling for gestational age at delivery. CONCLUSION: Neonatal complications of placenta previa included preterm birth, congenital anomalies, respiratory distress syndrome, and anemia. There was no increased occurrence of fetal growth restriction.

Am J Obstet Gynecol. 2003 May;188(5):1305-9. Placenta previa: neonatal death after live births in the United States. Salihu HM, Li Q, Rouse DJ, Alexander GR. PMID: 12748503

...DESIGN: This was a population-based retrospective cohort study of 1997 United States singleton live births...RESULTS: Of 3,773,369 live births, 9656 were complicated by placenta previa (2.6 cases per 1000). Among cases of placenta previa, 114 neonatal deaths occurred (11.8 per 1000) versus 14951 (4 per 1000) among non-placenta previa neonates (P <.0001). The adjusted relative risk of death was three times higher among placenta previa neonates (hazard ratio, 3.06; 95% CI, 2.40-3.94). Placenta previa-related death was mediated through preterm delivery rather than small for gestational age. CONCLUSION:Placenta previa triples the rate of neonatal mortality, which is mediated mainly through preterm birth.

Placenta Previa and Prior Cesarean

BMC Pregnancy Childbirth. 2011 Nov 21;11:95. doi: 10.1186/1471-2393-11-95. Risk of placenta previa in second birth after first birth cesarean section: a population-based study and meta-analysis. Gurol-Urganci I, Cromwell DA, Edozien LC, Smith GC, Onwere C, Mahmood TA, Templeton A, van der Meulen JH. PMID: 22103697

...METHODS: Retrospective cohort study of 399,674 women who gave birth to a singleton first and second baby between April 2000 and February 2009 in England...RESULTS: The rate of placenta previa at second birth for women with vaginal first births was 4.4 per 1000 births, compared to 8.7 per 1000 births for women with CS at first birth. After adjustment, CS at first birth remained associated with an increased risk of placenta previa (odds ratio = 1.60; 95% CI 1.44 to 1.76)....

Am J Obstet Gynecol. 1997 Nov;177(5):1071-8. The association of placenta previa with history of cesarean delivery and abortion: a metaanalysis. Ananth CV, Smulian JC, Vintzileos AM. PMID: 9396896

...RESULTS:...The tabulation of 36 studies identified a total of 3.7 million pregnant women, of whom 13,992 patients were diagnosed with placenta previa. The reported incidence of placenta previa ranged between 0.28% and 2.0%, or approximately 1 in 200 deliveries. Women with at least one prior cesarean delivery were 2.6 (95% confidence interval 2.3 to 3.0) times at greater risk for development of placenta previa in a subsequent pregnancy...Four studies, encompassing 170,640 pregnant women, provided data on the number of previous cesarean deliveries. These studies showed a dose-response pattern for the risk of previa on the basis of the number of prior cesarean deliveries. Relative risks were 4.5 (95% confidence interval 3.6 to 5.5) for one, 7.4 (95% confidence interval 7.1 to 7.7) for two, 6.5 (95% confidence interval 3.6 to 11.6) for three, and 44.9 (95% confidence interval 13.5 to 149.5) for four or more prior cesarean deliveries. ...CONCLUSION: There is a strong association between having a previous cesarean delivery, spontaneous or induced abortion, and the subsequent development of placenta previa. The risk increases with number of prior cesarean deliveries. Pregnant women with a history of cesarean delivery or abortion must be regarded as high risk for placenta previa and must be monitored carefully. This study provides yet another reason for reducing the rate of primary cesarean delivery and for advocating vaginal birth for women with prior cesarean delivery.

Obstet Gynecol. 2002 Jun;99(6):976-80. The likelihood of placenta previa with greater number of cesarean deliveries and higher parity. Gilliam M, Rosenberg D, Davis F. PMID: 12052584

...METHODS: A hospital-based, case-control study was conducted in which 316 multiparous women with placenta previa were identified. Controls consisted of 2051 multiparous women with spontaneous vaginal deliveries...RESULTS: Women with a prior cesarean delivery were more likely to have a placenta previa than those without (odds ratio [OR] 1.59, 95% confidence interval [CI] 1.21, 2.08). The likelihood of placenta previa increased as both parity and number of cesarean deliveries increased. Thus, the adjusted OR for a primiparous woman with one cesarean delivery was 1.28 (95% CI 0.82, 1.99). For a woman who has four or more deliveries with only a single cesarean delivery, the OR increases to 1.72 (95% CI 1.12, 2.64). This trend continues with greater parity and a greater number of cesarean deliveries such that the likelihood of placenta previa for a woman with parity greater than four and greater than four cesarean deliveries was OR 8.76 (95% CI 1.58, 48.53). CONCLUSION: This study supports the association between prior cesarean delivery and placenta previa and demonstrates that the joint effect of parity and prior cesarean delivery is greater than that of either variable alone.

Obstet Gynecol. 2006 Apr;107(4):771-8. Previous cesarean delivery and risks of placenta previa and placental abruption. Getahun D, Oyelese Y, Salihu HM, Ananth CV. PMID: 16582111

...METHODS: A retrospective cohort study of first 2 (n = 156,475) and first 3 (n = 31,102) consecutive singleton pregnancies using the 1989-1997 Missouri longitudinally linked data were performed...RESULTS: Rates of previa and abruption were 4.4 (n = 694) and 7.9 (n = 1,243) per 1,000 births, respectively. The pregnancy after a cesarean delivery was associated with increased risk of previa (0.63%) compared with a vaginal delivery (0.38%, RR 1.5, 95% confidence interval [CI] 1.3-1.8). Cesarean delivery in the first and second births conferred a two-fold increased risk of previa in the third pregnancy (RR 2.0, 95% CI 1.3-3.0) compared with first two vaginal deliveries...A second pregnancy within a year after a cesarean delivery was associated with increased risks of previa (RR 1.7, 95% CI 0.9-3.1) and abruption (RR 1.5, 95% CI 1.1-2.3). CONCLUSION: A cesarean first birth is associated with increased risks of previa and abruption in the second pregnancy. There is a dose-response pattern in the risk of previa, with increasing number of prior cesarean deliveries. A short interpregnancy interval is associated with increased risks of previa and abruption.

Obstet Gynecol. 2001 May;97(5 Pt 1):765-9. First-birth cesarean and placental abruption or previa at second birth (1). Lydon-Rochelle M, Holt VL, Easterling TR, Martin DP. PMID: 11339931

...METHODS: We conducted a population-based, retrospective cohort analysis using data from the Washington State Birth Events Record Database. The study cohort included all primiparas who gave birth to live singleton infants in nonfederal short-stay hospitals from January 1, 1987, through December 31, 1996, and who had second singleton births during the same period (n = 96,975)...RESULTS: Among our study cohort, abruptio placentae complicated 11.5 per 1000 and placenta previa 5.2 per 1000 singleton deliveries at second births. In logistic regression analyses adjusted for maternal age, women with first-birth cesareans had significantly increased risk of abruptio placentae (OR 1.3, 95% CI 1.1, 1.5), and placenta previa (OR 1.4, 95% CI 1.1, 1.6) at second births, compared with women with prior vaginal deliveries. CONCLUSION: We found moderately increased risk of placental abruption and previa as a long-term effect of prior cesarean delivery on second births.

BJOG. 2007 May;114(5):609-13. Epub 2007 Mar 12. Association of caesarean delivery for first birth with placenta praevia and placental abruption in second pregnancy. Yang Q, Wen SW, Oppenheimer L, Chen XK, Black D, Gao J, Walker MC. PMID: 17355267

...POPULATION: A total of 5,146,742 singleton second pregnancies were available for the final analysis after excluding missing information...RESULTS: Placenta praevia was recorded in 4.4 per 1000 second-birth singletons whose first births delivered by caesarean section and 2.7 per 1000 second-birth singletons whose first births delivered vaginally...The adjusted odds ratio (95% CIs) of previous caesarean section for placenta praevia in following second pregnancies was 1.47 (1.41, 1.52) after controlling for maternal age, race, education, marital status, maternal drinking and smoking during pregnancy, adequacy of prenatal care, and fetal gender...CONCLUSION: Caesarean section for first live birth is associated with a 47% increased risk of placenta praevia and 40% increased risk of placental abruption in second pregnancy with a singleton.

Obstet Gynecol. 1985 Jul;66(1):89-92. Placenta previa/accreta and prior cesarean section. Clark SL, Koonings PP, Phelan JP. PMID: 4011075

...the records of all patients presenting to labor and delivery with the diagnosis of placenta previa between 1977 and 1983 were examined. Of a total of 97,799 patients, 292 (0.3%) had a placenta previa. The risk of placenta previa was 0.26% with an unscarred uterus and increased almost linearly with the number of prior cesarean sections to 10% in patients with four or more. The effect of advancing age and parity on the incidence of placenta previa was much less dramatic. Patients presenting with a placenta previa and an unscarred uterus had a 5% risk of clinical placenta accreta. With a placenta previa and one previous cesarean section, the risk of placenta accreta was 24%; this risk continued to increase to 67% (two of three) with a placenta previa and four or more cesarean sections....

Int J Gynaecol Obstet. 1995 Oct;51(1):25-31. Placenta previa and previous cesarean section. To WW, Leung WC. PMID: 8582514

...METHOD: The records of all patients delivered with the diagnosis of placenta previa during the 10-year period from 1984 to 1993 were reviewed. RESULTS: From a total of 50,485 deliveries, 421 (0.83%) had placenta previa, 43 (10.2%) of whom had a history of previous cesarean section. The incidence of placenta previa was significantly increased in those with a previous cesarean section (1.31%) compared with those with an unscarred uterus (0.75%) (R.R. 1.64). This risk increased as the number of previous cesarean sections increased (R.R. 1.53 for one previous section, 2.63 for two or more). The incidence of an anterior placenta previa and placenta accreta was significantly increased in those with previous cesarean scars. The incidence of placenta accreta was 1.18% among patients with placenta previa, 80% being in patients with previous cesarean section. The relative risk for placenta accreta in patients with placenta previa was 35 times higher in those with a previous cesarean section than in those with an unscarred uterus. CONCLUSION: The association of previous cesarean section with placenta previa and placenta previa accreta is confirmed. Patients with an antepartum diagnosis of placenta previa who have had a previous cesarean section should be considered at high risk for developing placenta accreta.

Placental Complications Increase With Prior Cesarean

April was Cesarean Awareness Month.  It was sponsored by The International Cesarean Awareness Network (ICAN), which seeks to help support women after cesareans, to raise awareness of the implications of a high cesarean rate, and to keep Vaginal Birth After Cesarean (VBAC) an accessible choice for women.

As a follow-up to Cesarean Awareness Month, let's discuss some of the possible complications of too many cesareans.

The importance of this discussion is highlighted this week by the recent tragic story of a woman who died from complications of Placenta Accreta during her sixth cesarean.

The fact is that each successive cesarean increases the risk for abnormal implantation of the placenta in future pregnancies, and this can be life-threatening to both mother and baby.

This is not to imply that all cesareans are bad; many are truly life-saving and necessary, and many others are probably prudent.  However, many non-indicated cesareans are being done these days. Cesareans are not without risks and this mother's death shows why they should not be done without good reason, especially multiple repeat cesareans.

The extremely high cesarean rates and lack of VBAC access in certain areas of this country and around the world has very distinct public health implications that should not be ignored.

One of those public health implications is the rising incidence of placenta previa and placenta accreta.  As one study summarized:

Placenta accreta is recognized as a catastrophic disease in obstetrics. Diagnosed incidentally, it has been a rare disease in previous decades prior [to] indiscriminate use of cesarean delivery. The World Health Organization has recently highlighted this disease as a new pandemic, which is directly related to patients who have two or more caesarean sections.

Abnormal Placentation

One of the most significant risks after having had a cesarean section is abnormal placental implantation in a future pregnancy.  There are several different types of these, which include:

• Placenta Previa (the placenta implants too low, near or over the cervix)
• Placenta Accreta (the placenta attaches abnormally and has difficulty detaching later)
• Placenta Increta (the placenta grows into the uterine muscle and has difficulty detaching)
• Placenta Percreta (the placenta grows through the uterus and into surrounding organs)

In addition, there is an increased risk of the placenta pulling away from the uterine wall prematurely (called placental abruption).  This, too, can be a serious complication.

Today we'll discuss overall increases in placental complications after prior cesareans; in later posts, we'll discuss each placental complication in more detail.

The big question is why a subsequent pregnancy after cesarean is at risk for placental issues.  Although the exact mechanism is not clear, most authorities agree that the damage to the lining of the uterus from a cesarean may predispose to placental implantation and/or detachment issues, especially if the fertilized egg implants near the scarred area.

Of course, it's not just cesareans; any damage to the lining of the uterus can predispose to placental issues.  A D&C procedure, whether after a miscarriage or to terminate a pregnancy, can cause problems with the uterine lining.  On the other hand, research differs on whether myomectomy (fibroid removal) does or does not have an association with placental issues.

Even such minor factors as uterine infection, smoking, drug or alcohol use, older age, or many pregnancies can predispose to placental implantation issues.  The theory is that they also damage the uterine lining, causing problems when the next pregnancy implants.

However, it's clear from research that one of the most powerful risk factors for placental issues is a prior cesarean, and that the risk increases as the number of prior cesareans increases.  This means that this condition is often iatrogenic (caused by the physician) and is a preventable risk in many cases.

Increase in Placental Complications

Research shows that the incidence of placental complications has risen in parallel with the burgeoning cesarean rate.

For example, one recent study on placenta accreta shows that

The incidence of placenta accreta has increased 13-fold since the early 1900s and directly correlates with the increasing cesarean delivery rate.

Another study that did a meta-analysis of the impact of multiple repeat cesareans found:

The incidence of placenta previa increased from 10/1000 deliveries with 1 previous cesarean delivery to 28/1000 with ≥3 cesarean deliveries. 

Now, keep in mind that most women with three or more cesareans still don't experience a previa. However, to increase from an incidence of 1% to 2.8% is a serious increase, given the risks associated with previas.

The authors of that meta-analysis also pointed out that women with previa who have had prior cesareans are at far greater risk for the very serious condition of Placenta Accreta than women with previa who have not had prior cesareans.

Compared with women with previa and no previous cesarean delivery, women with previa and ≥3 cesarean deliveries had a statistically significant increased risk of accreta (3.3-4% vs 50-67%), hysterectomy (0.7-4% vs 50-67%), and composite maternal morbidity (15% vs 83%; odds ratio, 33.6; 95% confidence interval, 14.6-77.4). 

In other words, the risk for having both previa and accreta jumped from 3-4% to 50-70% if you had three or more prior cesareans.  Clearly, multiple cesareans strongly increase the risk for placental issues in future pregnancies.

Many of these studies use risk ratios to compare the risk. This is useful in some ways, but mothers deserve to know what the exact numerical risk is for these conditions.  A 2006 large study was able to quantify this for women. In their study, they found that accreta was present in:

• 0.24% of women undergoing their first cesarean
• 0.31% of women having their second cesarean
• 0.57% of women having their third cesarean
• 2.13% of women having their fourth cesarean
• 2.33% of women having their fifth cesarean
• 6.74% of women having their sixth or more cesarean

In addition, they found that a hysterectomy was required in:

• 0.65% of  women having their first cesarean 
• 0.42% of women having their second cesarean 
• 0.90% of women having their third cesarean
• 2.41% of women having their fourth cesarean 
• 3.49% of women having their fifth cesarean
• 8.99% of women having their sixth or more cesarean

Obviously, the more cesareans you have, the more at-risk you are for complications. Complications like previa and accreta really start to rise after 3-4 or more cesareans.

However, sometimes these complications happen when a woman has "only" had one or two prior cesareans.  One study found that having a cesarean for the first birth raised the risk for placental abruption in the second pregnancy by 40% and for placenta previa by 47%.  So although the risks are greatest with 3 or more cesareans, poor outcomes can happen even after only one or two cesareans.  That's why it's important to prevent every cesarean that is not truly medically-indicated.

Even more important is to prevent the automatic repeat cesarean that happens to most women in this country (and in many countries around the world).  In many areas now, once a woman has a cesarean, she is not "allowed" to choose (or is pressured out of) having a subsequent vaginal birth.  And this is what leads to many cases of placental complications.

Most women will not experience severe complications despite undergoing multiple cesareans, but some WILL ─ like the woman who died recently while having her sixth cesarean. Now her children have to grow up without their mother.

This is why it is so important to prevent that first cesarean whenever possible, and why it is absolutely critical for women to have access to VBAC instead of being forced into cesarean after cesarean.



References

Increase in Incidence of Abnormal Placentation

Obstet Gynecol Clin North Am. 2013 Mar;40(1):137-54. doi: 10.1016/j.ogc.2012.12.002. Placenta accreta, increta, and percreta. Wortman AC, Alexander JM.  PMID: 23466142

Placenta accreta is an abnormal adherence of the placenta to the uterine wall that can lead to significant maternal morbidity and mortality. The incidence of placenta accreta has increased 13-fold since the early 1900s and directly correlates with the increasing cesarean delivery rate. The prenatal diagnosis of placenta accreta by ultrasound along with risk factors including placenta previa and prior cesarean delivery can aid in delivery planning and improved outcomes. Referral to a tertiary care center and the use of a multidisciplinary care team is recommended.

Risk Factors for Abnormal Placentation

Am J Obstet Gynecol. 2005 May;192(5):1458-61. Abnormal placentation: twenty-year analysis. Wu S, Kocherginsky M, Hibbard JU.  PMID: 15902137

OBJECTIVE: This study was undertaken to determine whether the rate of abnormal placentation is increasing in conjunction with the cesarean rate and to evaluate incidence, risk factors, and outcomes...RESULTS: There were 64,359 deliveries, with cesarean rates increasing from 12.5% (1982) to 23.5% (2002). The overall incidence of placenta accreta was 1 in 533. Significant risk factors for placenta accreta in our final analysis included advancing maternal age (odds ratio [OR] 1.13, 95% CI 1.089-1.194, P < .0001), 2 or more cesarean deliveries (OR 8.6, 95% CI 3.536-21.078, P < .0001), and previa (OR 51.4, 95% CI: 10.646-248.390, P < .0001). CONCLUSION: The rate of placenta accreta increased in conjunction with cesarean deliveries; the most important risk factors were previous cesarean delivery, previa, and advanced maternal age.

PLoS One. 2012;7(12):e52893. doi: 10.1371/journal.pone.0052893. Epub 2012 Dec 27. Incidence and risk factors for placenta accreta/increta/percreta in the UK: a national case-control study. Fitzpatrick KE, Sellers S, Spark P, Kurinczuk JJ, Brocklehurst P, Knight M. PMID: 23300807

...METHODS: A national case-control study using the UK Obstetric Surveillance System was undertaken, including 134 women diagnosed with placenta accreta/increta/percreta between May 2010 and April 2011 and 256 control women. RESULTS: The estimated incidence of placenta accreta/increta/percreta was 1.7 per 10,000 maternities overall; 577 per 10,000 in women with both a previous caesarean delivery and placenta praevia. Women who had a previous caesarean delivery (adjusted odds ratio (aOR) 14.41, 95%CI 5.63-36.85), other previous uterine surgery (aOR 3.40, 95%CI 1.30-8.91), an IVF pregnancy (aOR 32.13, 95%CI 2.03-509.23) and placenta praevia diagnosed antepartum (aOR 65.02, 95%CI 16.58-254.96) had raised odds of having placenta accreta/increta/percreta. There was also a raised odds of placenta accreta/increta/percreta associated with older maternal age in women without a previous caesarean delivery (aOR 1.30, 95%CI 1.13-1.50 for every one year increase in age). CONCLUSIONS: Women with both a prior caesarean delivery and placenta praevia have a high incidence of placenta accreta/increta/percreta. There is a need to maintain a high index of suspicion of abnormal placental invasion in such women and preparations for delivery should be made accordingly.

Acta Obstet Gynecol Scand. 2013 Apr;92(4):457-60. doi: 10.1111/aogs.12080. Placenta accreta: incidence and risk factors in an area with a particularly high rate of cesarean section. Morlando M, Sarno L, Napolitano R, Capone A, Tessitore G, Maruotti GM, Martinelli P. PMID: 23347183

Placenta accreta is a rare and potentially life-threatening complication of pregnancy characterized by abnormal adherence of the placenta to the uterine wall. A previously scarred uterus or an abnormal site of placentation in the lower segment is a major risk factor. The aim of this study was to investigate the change in the incidence of placenta accreta and associated risk factors along four decades, from the 1970s to 2000s, in a tertiary south Italian center. We analyzed all cases of placenta accreta in a sample triennium for each decade. The incidence increased from 0.12% during the 1970s, to 0.31% during the 2000s. During the same period, cesarean section rates increased from 17 to 64%. Prior cesarean section was the only risk factor showing a significant concomitant rise. Our results reinforce cesarean section as the most significant predisposing condition for placenta accreta.

Placenta. 2012 Apr;33(4):244-51. doi: 10.1016/j.placenta.2011.11.010. Epub 2012 Jan 28. Placenta accreta: pathogenesis of a 20th century iatrogenic uterine disease. Jauniaux E, Jurkovic D. PMID: 22284667

Placenta accreta refers to different grades of abnormal placental attachment to the uterine wall, which are characterised by invasion of trophoblast into the myometrium. Placenta accreta has only been described and studied by pathologists for less than a century. The fact that the first detailed description of a placenta accreta happened within a couple of decades of major changes in the caesarean surgical techniques is highly suggestive of a direct relationship between prior uterine surgery and abnormal placenta adherence. Several concepts have been proposed to explain the abnormal placentation in placenta accreta including a primary defect of the trophoblast function, a secondary basalis defect due to a failure of normal decidualization and more recently an abnormal vascularisation and tissue oxygenation of the scar area. The vast majority of placenta accreta are found in women presenting with a previous history of caesarean section and a placenta praevia. Recent epidemiological studies have also found that the strongest risk factor for placenta praevia is a prior caesarean section suggesting that a failure of decidualization in the area of a previous uterine scar can have an impact on both implantation and placentation. Ultrasound studies of uterine caesarean section scar have shown that large and deep myometrial defects are often associated with absence of re-epithelialisation of the scar area. These findings support the concept of a primary deciduo-myometrium defect in placenta accreta, exposing the myometrium and its vasculature below the junctional zone to the migrating trophoblast. The loss of this normal plane of cleavage and the excessive vascular remodelling of the radial and arcuate arteries can explain the in-vivo findings and the clinical consequence of placenta accreta. Overall these data support the concept that abnormal decidualization and trophoblastic changes of the placental bed in placenta accreta are secondary to the uterine scar and thus entirely iatrogenic.

Placental Abruption and Prior Cesarean

Am J Perinatol. 2007 May;24(5):299-305. Epub 2007 May 18. Predicting placental abruption and previa in women with a previous cesarean delivery. Odibo AO, Cahill AG, Stamilio DM, Stevens EJ, Peipert JF, Macones GA. PMID: 17514600

The purpose of this study was to determine if placental abruption or previa in women with a history of a prior cesarean delivery (CD) can be predicted. A retrospective cohort study of pregnant women with previous CD was conducted in 17 centers between 1996 and 2000. Women developing placenta previa or abruption in the subsequent pregnancy were compared with those without these complications...Among 25,076 women with prior CD, there were 361 (15 per 1000 births) with placenta previa and 309 (13 per 1000 births) with abruption. The significant risk factors for these complications include advanced maternal age, Asian race, increased parity, illicit drug use, history of spontaneous abortion, and three or more prior cesarean deliveries. Prediction models for abruption and previa had poor sensitivity (12% and 13% for abruption and previa, respectively). In women with at least one prior cesarean delivery, the risk factors for placental previa and abruption can be identified. However, prediction models combining these risk factors were too inefficient to be useful.

Obstet Gynecol. 2006 Apr;107(4):771-8. Previous cesarean delivery and risks of placenta previa and placental abruption. Getahun D, Oyelese Y, Salihu HM, Ananth CV. PMID: 16582111

...METHODS: A retrospective cohort study of first 2 (n = 156,475) and first 3 (n = 31,102) consecutive singleton pregnancies using the 1989-1997 Missouri longitudinally linked data were performed. Relative risk (RR) was used to quantify the associations between cesarean delivery and risks of previa and abruption in subsequent pregnancies, after adjusting for several confounders. RESULTS: Rates of previa and abruption were 4.4 (n = 694) and 7.9 (n = 1,243) per 1,000 births, respectively. The pregnancy after a cesarean delivery was associated with increased risk of previa (0.63%) compared with a vaginal delivery (0.38%, RR 1.5, 95% confidence interval [CI] 1.3-1.8). Cesarean delivery in the first and second births conferred a two-fold increased risk of previa in the third pregnancy (RR 2.0, 95% CI 1.3-3.0) compared with first two vaginal deliveries. Women with a cesarean first birth were more likely to have an abruption in the second pregnancy (0.95%) compared with women who had a vaginal first birth (0.74%, RR 1.3, 95% CI 1.2-1.5). Two consecutive cesarean deliveries were associated with a 30% increased risk of abruption in the third pregnancy (RR 1.3, 95% CI 1.0-1.8). A second pregnancy within a year after a cesarean delivery was associated with increased risks of previa (RR 1.7, 95% CI 0.9-3.1) and abruption (RR 1.5, 95% CI 1.1-2.3). CONCLUSION: A cesarean first birth is associated with increased risks of previa and abruption in the second pregnancy. There is a dose-response pattern in the risk of previa, with increasing number of prior cesarean deliveries. A short interpregnancy interval is associated with increased risks of previa and abruption.

BJOG. 2007 May;114(5):609-13. Epub 2007 Mar 12. Association of caesarean delivery for first birth with placenta praevia and placental abruption in second pregnancy. Yang Q, Wen SW, Oppenheimer L, Chen XK, Black D, Gao J, Walker MC. PMID: 17355267

...SETTING: Linked birth and infant mortality database of the USA between 1995 and 2000. POPULATION: A total of 5,146,742 singleton second pregnancies were available for the final analysis after excluding missing information...RESULTS: Placenta praevia was recorded in 4.4 per 1000 second-birth singletons whose first births delivered by caesarean section and 2.7 per 1000 second-birth singletons whose first births delivered vaginally. About 6.8 per 1000 births were complicated with placental abruption in second-birth singletons whose first births delivered by caesarean section and 4.8 per 1000 birth in second-birth singletons whose first births delivered vaginally. The adjusted odds ratio (95% CIs) of previous caesarean section for placenta praevia in following second pregnancies was 1.47 (1.41, 1.52) after controlling for maternal age, race, education, marital status, maternal drinking and smoking during pregnancy, adequacy of prenatal care, and fetal gender. The corresponding figure for placental abruption was 1.40 (1.36, 1.45). CONCLUSION: Caesarean section for first live birth is associated with a 47% increased risk of placenta praevia and 40% increased risk of placental abruption in second pregnancy with a singleton.

Risks of Multiple Repeat Cesareans

Am J Obstet Gynecol. 2011 Dec;205(6 Suppl):S2-10. doi: 10.1016/j.ajog.2011.09.028. Epub 2011 Oct 6. Long-term maternal morbidity associated with repeat cesarean delivery. Clark EA, Silver RM. PMID: 22114995

Concern regarding the association between cesarean delivery and long-term maternal morbidity is growing as the rate of cesarean delivery continues to increase. Observational evidence suggests that the risk of morbidity increases with increasing number of cesarean deliveries. The dominant maternal risk in subsequent pregnancies is placenta accreta spectrum disorder and its associated complications. A history of multiple cesarean deliveries is the major risk factor for this condition. Pregnancies following cesarean delivery also have increased risk for other types of abnormal placentation, reduced fetal growth, preterm birth, and possibly stillbirth. Chronic maternal morbidities associated with cesarean delivery include pelvic pain and adhesions. Adverse reproductive effects may include decreased fertility and increased risk of spontaneous abortion and ectopic pregnancy. Clinicians and patients need to be aware of the long-term risks associated with cesarean delivery so that they can be considered when determining the method of delivery for first and subsequent births.

 BJOG. 2013 Jan;120(1):85-91. doi: 10.1111/1471-0528.12010. Epub 2012 Oct 24.
Multiple repeat caesarean section in the UK: incidence and consequences to mother and child. A national, prospective, cohort study. Cook JR, Jarvis S, Knight M, Dhanjal MK. PMID: 23095012

...SETTING: All UK hospitals with consultant-led maternity units. POPULATION: Ninety-four women having their fifth or greater MRCS between January 2009 and December 2009, and 175 comparison women having their second to fourth caesarean section...RESULTS:...Women with MRCS had significantly more major obstetric haemorrhages (>1500 ml) (aOR, 18.6; 95% CI, 3.89-88.8), visceral damage (aOR, 17.6; 95% CI, 1.85-167.1) and critical care admissions (aOR, 15.5; 95% CI, 3.16-76.0), than women with lower order repeat caesarean sections. These risks were greatest in the 18% of women with MRCS who also had placenta praevia or accreta. Neonates of mothers having MRCS were significantly more likely to be born prior to 37 weeks of gestation (OR, 6.15; 95% CI, 2.56-15.78) and therefore had higher rates of complications and admissions. CONCLUSIONS: MRCS is associated with greater maternal and neonatal morbidity than fewer caesarean sections. The associated maternal morbidity is largely secondary to placenta praevia and accreta, whereas higher rates of preterm delivery are most likely a response to antepartum haemorrhage.

Semin Perinatol. 2012 Oct;36(5):315-23. doi: 10.1053/j.semperi.2012.04.013. Implications of the first cesarean: perinatal and future reproductive health and subsequent cesareans, placentation issues, uterine rupture risk, morbidity, and mortality. Silver RM.  PMID: 23009962

Rates of cesarean delivery have substantially increased worldwide during the past 30 years. Indeed, almost one-third of deliveries in the United States are cesareans. Most cesareans are safe, and major complications are uncommon. However, there is a "concealed" downside to cesarean deliveries. There are rare but life-threatening morbidities that may occur, which are often overlooked because most cesareans go well. In addition, subsequent pregnancies are fraught with an increased risk of both maternal and fetal complications. The worst of these are associated with placental problems such as previa, abruption, and accreta. The risk dramatically worsens in patients with multiple repeat cesarean deliveries. This article will summarize and highlight the implications of the rising cesarean rate on maternal and fetal morbidity and mortality. 

Am J Obstet Gynecol. 2011 Sep;205(3):262.e1-8. doi: 10.1016/j.ajog.2011.06.035. Epub 2011 Jun 15. Impact of multiple cesarean deliveries on maternal morbidity: a systematic review. Marshall NE, Fu R, Guise JM. PMID: 22071057

...RESULTS: Twenty-one studies (2,282,922 deliveries) were included. The rate of hysterectomy, blood transfusions, adhesions, and surgical injury all increased with increasing number of cesarean deliveries. The incidence of placenta previa increased from 10/1000 deliveries with 1 previous cesarean delivery to 28/1000 with ≥3 cesarean deliveries. Compared with women with previa and no previous cesarean delivery, women with previa and ≥3 cesarean deliveries had a statistically significant increased risk of accreta (3.3-4% vs 50-67%), hysterectomy (0.7-4% vs 50-67%), and composite maternal morbidity (15% vs 83%; odds ratio, 33.6; 95% confidence interval, 14.6-77.4). CONCLUSION: Serious maternal morbidity progressively increased as the number of previous cesarean deliveries increased.

Obstet Gynecol. 2013 Apr;121(4):789-97. doi: 10.1097/AOG.0b013e3182878b43. Consequences of a primary elective cesarean delivery across the reproductive life. Miller ES, Hahn K, Grobman WA; Society for Maternal-Fetal Medicine Health Policy Committee. PMID: 23635679

OBJECTIVE: To estimate cumulative risks of morbidity associated with the choice of elective cesarean delivery for a first delivery. METHODS: A decision analytic model was designed to compare major adverse outcomes across a woman's reproductive life associated with the choice of elective cesarean delivery compared with a trial of labor at a first delivery. Maternal outcomes assessed included maternal transfusion, hysterectomy, thromboembolism, operative injury, and death. Neonatal outcomes assessed included cerebral palsy and permanent brachial plexus palsy in the offspring. RESULTS: Choosing an initial cesarean delivery resulted in a 0.3% increased risk of a major adverse maternal outcome in the first pregnancy. In each subsequent pregnancy, the difference in composite maternal morbidity increased such that by the fourth pregnancy, the cumulative risk of a major adverse maternal outcome was nearly 10% in the elective primary cesarean delivery group, three times higher than women who initially underwent a trial of labor. Although the choice of an initial cesarean delivery resulted in 2.4 and 0.41 fewer cases of cerebral palsy and brachial plexus palsy, respectively, per 10,000 women in the first pregnancy, by a fourth pregnancy, the risk of a adverse neonatal outcome was higher among offspring of women who had chosen the initial elective cesarean delivery (0.368% compared with 0.363%). CONCLUSION: Maternal morbidity associated with the choice of primary elective cesarean delivery increases in each subsequent pregnancy and is greater in magnitude than that associated with the choice of a trial of labor. These increased risks are not offset by a substantive reduction in the risk of neonatal morbidity.