Induction's Relationship to Cesareans in High BMI Women

Many providers are so affected by the over-hyping of risk around pregnancy in women of size that they routinely induce labor in "obese" women for basically no other real reason than the woman's BMI.

But a recently-published Canadian study shows there is yet another reason to be cautious about routinely inducing labor in obese women─ an increased risk of cesarean.

Yet the authors completely missed the obvious take-home message from their study ─ reduce the number of inductions done in obese women ─ and instead call for more weight-loss intervention efforts in order to prevent cesareans. Doh!

As part of Cesarean Awareness Month, let's take yet another look at the relationship between induction of labor and high cesarean rates in obese women.

Caregivers interested in lowering cesarean rates in higher-weight women would likely get the most effective results by changing management of this group rather than focusing on weight loss efforts.

When will caregivers finally clue in to the fact that they need other tools in the cesarean prevention toolbox besides weight loss? Changing their own management behaviors is the key to lowering cesarean rates in obese women, not getting women all to "normalize" their pre-pregnancy weight.

Let's be clear. It's reasonable to encourage healthy eating and regular exercise in women before they conceive, but that doesn't usually result in significant weight loss. Research shows that only a small percentage of people lose a substantial amount of weight and keep it off. It's unrealistic to insist that women all reach a certain BMI before pregnancy. And it's incredibly foolish to hang all your hopes for lowering cesarean rates on that goal.

There are other, more powerful tools in the toolbox for that. First and foremost among them is changing behaviors around induction of labor in this group.

Background

Induction is a very common intervention used in women of size, as I have pointed out many times before. And there is quite a bit of research suggesting that induction is tied to a higher cesarean rate, especially in first-time mothers or in women with an unripe cervix.

Of course, it's only fair to point out that sometimes induction really is needed in women of size. High-BMI women have a higher rate of pre-eclampsia (blood pressure issues), for example, as this study also found. This often necessitates early induction of labor because pre-eclampsia is very serious and can harm both mother and baby.

But high-BMI women are often induced at far higher rates than their complications justify.

Often these inductions are done for "soft" reasons that are highly questionable medically.

For example, many providers induce labor in obese women because they are afraid of big babies, even though research shows that inducing labor does not improve outcomes at all and often worsens them. The combination of obese first-time mother, a suspected big baby, and induction of labor is particularly potent, doubling the risk for cesarean even in a usually low-intervention midwifery practice.

Often providers induce labor because they believe that pregnancy in a fat woman is a disaster waiting to happen, and that labor should be brought on as soon as possible before an emergency occurs. Sadly, all too often, such perceptions often become self-fulfilling prophecies because of the huge amount of interventions employed, which also carry significant risk.

Some providers induce labor because they mistakenly believe that fat women are unlikely to go into labor on their own. Research shows that higher-weight women do have many inductions for "post-dates" pregnancies and that these inductions are more likely to result in cesareans, but rarely do care providers adjust a high-BMI mother's due date to reflect the fact that many have longer menstrual cycles.

Some induce labor in the belief that fat women are too out of shape to endure a natural labor and birth. Others induce labor because they mistakenly believe inducing labor is the only way that higher weight women will have any chance at having a vaginal birth because of ""fat pads" in the pelvis" or a "fat" vagina. These assumptions are all wrong, mind, but subtle bias like this influences how higher-weight women are managed.

For these and many other reasons, providers tend to over-use inductions in women of size. Although most in the medical field never question the high utilization of inductions in obese women, there are finally now a few researchers who have begun to question this practice.

New Study Findings

A new Canadian study highlights just how many obese women have their labor induced.

Less than a third of average-weight women in the study had their labor induced, but almost HALF of higher weight women had their labor induced. No doubt some of those inductions in the high-BMI group were medically justified, but chances are that many more were not.

Most notably, this study shows that induction in obese women often leads to cesareans.

I've been saying for years that over-use of induction in obese women is one of the main reasons for a high cesarean rate in this group, yet few researchers have bothered to look at this connection or to call for fewer inductions in this group. Many ignore their own findings that inductions are tightly tied to cesarean rates in this group. Finally, now, some researchers are beginning to pay attention.

Of particular note, this Canadian study found that when covariates were controlled for, Body Mass Index (BMI) was not a significant risk factor for cesareans in women with spontaneous labor. 

This is in contrast to the false belief among many providers that obesity often prevents vaginal birth due to "soft tissue dystocia." But in this study, higher weight alone did NOT raise the risk for cesarean ─ when labor was spontaneous.

However, obesity DOUBLED the risk for cesareans during inductions. According to the study:

Obese women were twice more likely (aOR 2.2, CI 1.2-4.1) to deliver by emergency C-section if their labour was induced...The twofold increase in the risk of C-section rates in obese women after induction was independent of pregnancy complications, parity, prior caesarean deliveries, chronic maternal health conditions, treatments for infertility, or maternal age.

That's a really important distinction. A higher weight itself did not increase the risk for cesareans when labor was spontaneous, but when labor was induced, it did. And this was independent of pregnancy complications and other factors that might also increase the risk for cesarean.

This suggests that induction itself (and decision-making during induction) was more of a real factor than the obesity itself.

For example, previous studies have found a lower threshold for surgical intervention in high-BMI patients. Many obese women would probably benefit from their caregivers simply waiting longer before opting for a cesarean. Others would probably benefit more from caregivers waiting for the mother's cervix to be fully ripe before labor was induced.

But most likely, obese women would probably benefit MOST from a lower induction rate. 

Sometimes, induction truly is necessary, and women of size do have higher rates of some complications that make induction a consideration. But many women of size are being induced for dubious reasons, mostly reflecting subtle provider bias and fear rather than true medical indications. These "soft" inductions need to STOP. If inductions are used, they should ideally wait until the cervix is ripe and caregivers should employ more patience in labor before resorting to a cesarean.

Lowering the number of inductions done and changing the management of inductions when they are done should help lower the outrageously high cesarean rates in obese women.

Focus on Realistic Change

To summarize, several recent studies have observed that caregivers often use a high rate of interventions during labor with their obese patients and have questioned whether this is truly beneficial. The authors of this recent Canadian study also noted that:

Even among women with term, singleton pregnancies obtaining prenatal care in community-based settings, obese women who undergo labour induction are at increased risk of obstetrical interventions at delivery...Although obesity in pregnancy is not an independent justification for labour induction, obese women are more likely to be induced and if induced are more likely to undergo delivery by C-section.

Astoundingly, the authors of the Canadian study then completely missed the mark in evaluating their findings. Like many in the obstetrical field, their response was NOT to call for fewer inductions, but rather to call for increased weight loss interventions prior to pregnancy.

What?!?!? Once again, the researchers missed a tremendous opportunity for improving outcomes in higher-weight women because they can't see beyond their own relentless focus on weight loss.

Rather than focusing their efforts on the unlikely success of weight-loss interventions, caregivers should be focusing on lowering the induction rate in this group and changing their threshold for surgical intervention. 

THOSE are the interventions most likely to bring about fewer cesareans.

Several studies have found that inductions are tightly tied to elevated cesarean rates in high-BMI women, and when induction is controlled for, the differences in cesarean rates are much smaller or disappear entirely. Induction is the root of the problem, independent from obesity itself.

Additionally, several studies over the years have found that when induction is frequently used with obese women, it often is the starting point for other poor outcomes.

If you want to improve outcomes in obese women, start by addressing the high induction rate, especially in first-time mothers. 

A few researchers are beginning to get it. A recent American study found that first-time obese mothers induced at term had a much higher cesarean rate (40% vs. 25%) and a higher rate of neonatal admissions to the NICU than those obese women who were managed expectantly. They concluded:

Elective labor induction at term in obese nulliparous parturients carries an increased risk of cesarean delivery and higher neonatal intensive care unit admission rate as compared with expectant management.

A major Irish study recently recommended that inductions only be undertaken for strict indications in obese women:

Due to the short-term and long-term implications of an unsuccessful induction in an obese primigravida, we recommend that induction of labor should only be undertaken for strict obstetric indications after careful consideration by an experienced clinician.

One recent French review concluded:

It may be possible to reduce primary and thus repeat cesarean delivery rates among obese women by preventive actions targeting labor induction in primiparous women and prelabor cesarean deliveries in multiparous women.

Bottom line, care providers need to be much more cautious about the amount of interventions they employ in the pregnancies of higher weight women.

In particular, induction of labor should be avoided when not truly medically indicated, especially in first-time mothers. If it occurs, it should usually wait until a woman's Bishop Score indicates a ripe cervix, and more patience during labor should be employed before moving to a cesarean section. 

These changes, rather than browbeating women about weight loss interventions, will be the ones that bring about the biggest improvements in outcome for women of size.


References

BMC Pregnancy Childbirth. 2014 Dec 20;14(1):422. [Epub ahead of print] Pre-pregnancy Body Mass Index (BMI) and delivery outcomes in a Canadian population. Vinturache A, Moledina N, McDonald S, Slater D, Tough S. PMID: 25528667

...This study is a secondary analysis of the All Our Babies Cohort, a prospective, community-based pregnancy cohort in Calgary, Alberta...(n=1996)...Women with increased pre-pregnancy BMI were more likely to develop pregnancy complications such as preeclampsia (OR 3.5, CI 2.0-4.6 for overweight; OR 5.3, CI 3.3-8.5 for obese) and gestational diabetes (OR 3.0, CI 1.8-5.0 for overweight; OR 6.5, CI 3.7-11.2, for obese) than normal weight women. Spontaneous onset of labour was recorded in 71.2% of women with normal pre-pregnancy BMI, whereas 39.3% of overweight and 49% of obese women had their labour induced. For women with spontaneous labour, pre-pregnancy BMI was not a significant risk factor for mode of delivery, controlling for covariates. Among women with induced labor, obesity was a significant risk factor for delivery by C-section (adjusted OR 2.2; CI 1.2-4.1). CONCLUSIONS: Even among women with term, singleton pregnancies obtaining prenatal care in community-based settings, obese women who undergo labour induction are at increased risk of obstetrical interventions at delivery....

Am J Obstet Gynecol. 2014 Jul;211(1):53.e1-5. doi: 10.1016/j.ajog.2014.01.034. Epub 2014 Jan 31. Risk of cesarean in obese nulliparous women with unfavorable cervix: elective induction vs expectant management at term. Wolfe H1, Timofeev J2, Tefera E3, Desale S3, Driggers RW2. PMID: 24486226

OBJECTIVE: The objective of the study was to examine maternal and neonatal outcomes in obese nulliparous women with an unfavorable cervix undergoing elective induction of labor compared with expectant management after 39.0 weeks. STUDY DESIGN: This was a retrospective analysis of a cohort of nulliparous women with a vertex singleton gestation who delivered at MedStar Washington Hospital Center from 2007 to 2012. Patients with unfavorable cervix between 38.0 and 38.9 weeks (modified Bishop <5) and a body mass index of 30.0 kg/m(2) or greater at the time of delivery were included. Women undergoing elective induction between 39.0 and 40.9 weeks' gestation were compared with those who were expectantly managed beyond 39.0 weeks...RESULTS: Sixty patients meeting inclusion criteria underwent elective induction of labor and were compared with 410 patients expectantly managed beyond 39.0 weeks. The rate of cesarean delivery was significantly higher in the electively induced group (40.0% vs 25.9%, respectively, P = .022)...The neonatal intensive care unit admission rate was higher in the electively induced group (18.3% vs 6.3%, P = .001)...CONCLUSION: Elective labor induction at term in obese nulliparous parturients carries an increased risk of cesarean delivery and higher neonatal intensive care unit admission rate as compared with expectant management.

Am J Obstet Gynecol. 2015 Feb;212(2):241.e1-9. doi: 10.1016/j.ajog.2014.08.002. Epub 2014 Aug 6. The risk of prelabor and intrapartum cesarean delivery among overweight and obese women: possible preventive actions. Hermann M1, Le Ray C2, Blondel B3, Goffinet F2, Zeitlin J3. PMID: 25108139

...We modeled relative risks (RRs) and risk differences of prelabor and intrapartum cesarean delivery by prepregnancy body mass index (obese, ≥30 kg/m(2); overweight, 25-29.9 kg/m(2); normal weight, 18.5-24.9 kg/m(2)) in a nationally representative sample of 12,297 French women. Models were stratified by parity and previous cesarean status. Covariates included maternal sociodemographic characteristics, medical conditions, pregnancy complications, and induction of labor. RESULTS:...Increased intrapartum cesarean delivery risks for primiparous women were related to more frequent labor induction (42.6% vs 23.8% for normal-weight women). CONCLUSION: It may be possible to reduce primary and thus repeat cesarean delivery rates among obese women by preventive actions targeting labor induction in primiparous women and prelabor cesarean deliveries in multiparous women. Further research is needed on the impact of limiting inductions on cesarean delivery risks for obese primiparous women.

Acta Obstet Gynecol Scand. 2013 Dec;92(12):1414-8. doi: 10.1111/aogs.12263. Maternal obesity and induction of labor. O'Dwyer V1, O'Kelly S, Monaghan B, Rowan A, Farah N, Turner MJ. PMID: 24116732

...Compared with women with a normal BMI, obese primigravidas but not obese multigravidas were more likely to have labor induced. In primigravidas who had labor induced, the cesarean section rate was 20.6% (91/442) compared with 8.3% (17/206) in multigravidas who had labor induced (p < 0.001). In obese primigravidas, induction of labor was also more likely to be associated with other interventions such as epidural analgesia, fetal blood sampling and emergency cesarean section. In contrast, induction of labor in obese multigravidas was not only less common but also not associated with an increase in other interventions compared with multigravidas with a normal BMI. CONCLUSIONS: Due to the short-term and long-term implications of an unsuccessful induction in an obese primigravida, we recommend that induction of labor should only be undertaken for strict obstetric indications after careful consideration by an experienced clinician.

J Midwifery Womens Health. 2014 Jan-Feb;59(1):43-53. doi: 10.1111/jmwh.12073. Epub 2014 Jan 8. Intrapartum management associated with obesity in nulliparous women. Carlson NS, Lowe NK. PMID: 24400789

...Intrapartum interventions used significantly more often for healthy, obese nulliparous women when compared with normal-weight women were induction of labor, augmentation of labor, and cesarean birth. It is unclear if assisted vaginal birth occurs more frequently among obese women. Epidural anesthesia, artificial rupture of membranes prior to 6 cm of cervical dilation, and early hospital admission were shown in separate studies to be used more often in obese women. Intrapartum interventions were used more frequently in obese women in a dose-dependent manner by body mass index...Implications for clinical practice from this systematic review are that healthy, nulliparous obese women are exposed to common intrapartum interventions more often than normal-weight women. In the absence of evidence on the use of appropriate use of intrapartum interventions in this population, health care providers should carefully monitor management choices when working with healthy, nulliparous obese women.

BJOG. 2005 Jun;112(6):768-72. Outcome of pregnancy in a woman with an increased body mass index. Usha Kiran TS1, Hemmadi S, Bethel J, Evans J. PMID: 15924535

...The study sample was drawn from the Cardiff Births Survey, a population-based database comprising of a total of 60,167 deliveries in the South Glamorgan area between 1990 and 1999...RESULTS: We report an increased risk [quoted as odds ratio (OR) and confidence intervals CI)] of postdates, 1.4 (1.2-1.7); induction of labour, 1.6 (1.3-1.9); caesarean section, 1.6 (1.4-2); macrosomia, 2.1 (1.6-2.6); shoulder dystocia, 2.9 (1.4-5.8); failed instrumental delivery, 1.75 (1.1-2.9); increased maternal complications such as blood loss of more than 500 mL, 1.5 (1.2-1.8); urinary tract infections, 1.9 (1.1-3.4); and increased neonatal admissions with complications such as neonatal trauma, feeding difficulties and incubator requirement. CONCLUSION: Obese women appear to be at risk of intrapartum and postpartum complications. Induction of labour appears to be the starting point in the cascade of events....

J Obstet Gynaecol Can. 2011 May;33(5):443-8. Higher caesarean section rates in women with higher body mass index: are we managing labour differently? Abenhaim HA, Benjamin A. PMID: 21639963

BACKGROUND: Higher body mass index has been associated with an increased risk of Caesarean section. The effect of differences in labour management on this association has not yet been evaluated. METHODS: We conducted a cohort study using data from the McGill Obstetrics and Neonatal Database for deliveries taking place during a 10-year period...RESULTS: Data were available for 11 922 women, of whom 2289 women had normal weight, 5663 were overweight, 3730 were obese, and 240 were morbidly obese. After adjustment for known confounding variables, increased BMI category was associated with an overall increase in the use of oxytocin and in the use of epidural analgesia, and with a decrease in use of forceps and vacuum extraction among second stage deliveries. Higher BMI was also found to be associated with earlier decisions to perform a Caesarean section in the second stage of labour. When adjusted for these differences in the management of labour, the increasing rate of Caesarean section observed with increasing BMI category was markedly attenuated (P less than 0.001). CONCLUSION: Women with an increased BMI are managed differently in labour than women of normal weight. This difference in management in part explains the increased rate of Caesarean section observed with higher BMI.

Aust N Z J Obstet Gynaecol. 2011 Apr;51(2):172-4. Impact of morbid obesity on the mode of delivery and obstetric outcome in nulliparous singleton pregnancy and the implications for rural maternity services. Green C, Shaker D. PMID: 21466521

...We conclude that morbid obesity is associated with a significantly higher risk of pre-existing medical conditions, developing antenatal complications, induction of labour, caesarean section and greater birth weight. However, there was no significant difference in caesarean section rates when adjusted for induction of labour....