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.