Induction or Waiting in Obese First-Time Mothers?

This is a follow-up post about a study reported on briefly here earlier this year.

It is about the question of whether "obese" women should have their labors induced proactively at term or be expectantly managed, and whether elective induction increases their risk for cesarean and other poor outcomes (like fetal distress, more Neonatal Intensive Care Unit utilization, etc.).

Induction of Labor: Help or Harm?

Induction of labor is an increasingly common intervention in women of all sizes. The question is whether it does more harm than good.

Much research shows it is associated with an increased risk for cesarean, but other research does not always show this. A definitive answer still eludes us on whether/when induction is appropriate.

Complicating this question is the whether or not the mother's cervix is ripe. Inducing on a very ripe cervix is much less likely to lead to a cesarean than inducing on an unripe cervix (Bishop Score less than 5-7, or cervical dilation more than 3 or 4).  And this is especially true in first-time mothers (nulliparous women).

An increased maternal BMI complicates this debate because of a perceived heightening of risk. One of the biggest dilemmas facing maternity care providers who are caring for "obese" women is how to manage them at term. Should they electively induce labor at 39 or 40 weeks, or should they wait for labor to start on its own if no complications occur?

Many care providers these days seem to be electively inducing obese women at 39 or 40 weeks, sometimes regardless of cervical ripeness (when they are not trying to talk them into a planned cesarean).

Many have the best intentions with this; they think inducing a smaller baby will lessen the risk for cesarean or shoulder dystocia, or they think that baby will have better outcomes if they induce before complications might develop. But do these assumptions hold up under scrutiny?

The problem is that little research has actually examined the question of whether it is beneficial to routinely induce obese mothers without specific medical indications for induction.

Care providers usually go ahead and do so, assuming that inducing obese women at term is beneficial, but there has been little direct evidence one way or the other in a study specifically designed to look at the benefits and risks of routine elective induction in high-BMI women.

Sadly, there is still no large study that rigorously examines this question.

However, we now have a small study that begins to address it. The study looks at the outcomes of elective induction or expectant management of obese first-time mothers with an unripe cervix.

The Study

This retrospective study was conducted by doctors at a hospital in Washington D.C. They studied obese (BMI 30 or more) first-time mothers with no chronic medical co-morbidities (like chronic hypertension, pre-existing diabetes, etc.). Women were admitted to the study between 39 and 41 weeks, and only if they had an unripe cervix (Bishop score less than 5) that was documented during week 38.

The researchers compared the results of electively inducing obese first-time mothers with an unripe cervix (n=60) at 39-41 weeks with expectant management (waiting for spontaneous labor or inducing only if medical indications arose, n=410). Age, BMI at delivery, and prenatal weight gain were similar between groups.

It's important to note that the authors did not compare elective induction to only spontaneous labor. They compared elective induction to expectant management, many of whom eventually were induced if medical indications for induction of labor arose.

The results of this study would probably be even more striking if they compared elective induction only to spontaneous labor, but the authors felt that this was not an appropriate comparison, stating,
"Because spontaneous labor is not something a provider can choose for a patient, it is not realistic to use this as a comparison control group; it is more appropriate to compare the induction of labor to expectant management."

Even so, the bottom line was that the researchers found that electively inducing labor in high-BMI first-time mothers with an unripe cervix raised the risk for cesarean. By quite a bit.

The cesarean rate was 25.9% in the obese women in the expectant management group, and the cesarean rate was 40% in the elective induction group.

That's a significant increase in risk for cesarean.

Only 10.7% of women in the expectant management group were still pregnant by 41 weeks; all the others had either gone into labor spontaneously (36.8%) or had been induced for commonly-accepted medical indications (rupture of membranes, gestational hypertension, non-reassuring fetal heart rate tracings, etc.). So quite a few of the expectant management group were eventually induced, yet the difference in the cesarean rate was still quite marked.

Another important finding was that the elective induction group had three times the rate of admission to the Neonatal Intensive Care Unit (NICU) after the birth (18.3% vs. 6.3%).

This suggests that instead of reducing harm to the baby (as many care providers believe), elective induction in this population may actually increase the risks of poor outcomes.

Now, of course the study had a relatively small sample size, especially in the electively induced group. It was also a retrospective study. So the authors point out that further research on this topic is needed, preferably with a large prospective study.

Still, even with the study's weaknesses, it suggests strong caution towards elective induction in obese women with an unripe cervix. As the authors note:

In a joint summary from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the Society for Maternal-Fetal Medicine, and the American College of Obstetricians and Gynecologists, physicians are urged to perform labor induction primarily for a medical indication and if done for nonmedical indications...to ensure that the 'cervix should be favorable, especially in the nulliparous patient.' Our findings support this assertion.

Other studies 

This study echoes a number of studies which have found higher c-section rates and complications in obese women who were induced (especially first-time obese mothers).

Of course, these studies did not specifically examine the question of whether routine induction in obese women improved overall outcomes. Still, their findings seem to also suggest caution around the idea of routine induction in obese women.

Although a higher rate of complications like pre-eclampsia means that some obese women will be induced for true medical indications, many others are induced for more dubious indications, based on questionable beliefs. These must be examined carefully.

For example, many providers believe that inducing early when the baby is smaller will lessen the risk for cesarean. Yet a number of studies have shown that it actually increases the risk for cesarean.

The combination of a suspected big baby and a high-BMI mother is a particularly potent combination that leads to many cesareans. A 2006 Massachusetts study found that the combination of induction, a suspected big baby, and first-time mother doubled the cesarean rate in the high-BMI women studied.

Many women of size are induced labor at term ostensibly to prevent a shoulder dystocia. Yet a recent New York study found that induction of labor actually increased the risk for shoulder dystocia (2.85x the risk), and especially so in obese women (5.64x the risk). By inducing women of size, providers may often be creating the very situation they are trying to avoid.

Other care providers induce because they believe it will improve outcomes in high-BMI women. A 2005 Welsh study on obese women with no complications found that the cesarean rate was 19% in the group with spontaneous labor and 41% in the induced group. Like in the present study, the Welsh study noted that the induction of labor was the start of many problems for the obese women in the group, including more blood loss, more UTIs, more babies in the NICU, more feeding difficulties, more neonatal trauma, etc.

So while many care providers think they are doing obese women a favor by inducing them proactively at term, there is strong reason to suspect that they may actually be doing more harm than good.

So much so that a 2013 Irish study (which found higher rates of emergency cesarean in induced obese first-time mothers) concluded:

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.

Conclusion

Research is clear that induction of labor is an extremely common intervention in obese women.

These and other studies suggest that perhaps a little more time and patience is needed at the end of pregnancy in obese women, and that induction should only be undertaken for strict medical indications.

Furthermore, it is time that larger studies directly address the question of whether routine induction at term improves or harms outcomes in obese women and their babies.

These potential studies should particularly look at outcomes among subsets of high-BMI populations, including obese women with complications and those without, those with differing levels of obesity, obese first-time mothers with an unripe cervix, obese multips with a prior vaginal birth, obese women where a big baby is suspected, etc.

Only then will care providers receive clearer guidance on the best management of women of size at term in many of the scenarios they are likely to encounter. It's FAR past time for such targeted research to occur.

We need care based on real evidence, not simply on assumptions about what's best for obese women.


References

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). Other maternal outcomes, including operative vaginal delivery, rate of third- or fourth-degree lacerations, chorioamnionitis, postpartum hemorrhage, and a need for a blood transfusion were similar. The neonatal intensive care unit admission rate was higher in the electively induced group (18.3% vs 6.3%, P = .001). Birthweight, umbilical artery pH less than 7.0, and Apgar less than 7 at 5 minutes were similar. 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.

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

...Of 2000 women enrolled, 50.4% (n = 1008) were primigravidas and 17.3% (n = 346) were obese. The induction rate was 25.6% and the overall cesarean section rate 22.0%. Primigravidas were more likely to have labor induced than multigravidas (38.1% vs. 23.4%, p < 0.001). 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.

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. POPULATION: Primigravid women with a singleton uncomplicated pregnancy with cephalic presentation of 37 or more weeks of gestation... METHODS: Comparisons were made between women with a body mass index of 20-30 and those with more than 30...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 Midwifery Womens Health. 2006 Jul-Aug;51(4):254-9. Maternal body mass index, delivery route, and induction of labor in a midwifery caseload. Graves BW1, DeJoy SA, Heath A, Pekow P. PMID: 16814219

...This retrospective cohort study examined the outcomes of 1500 consecutively delivered women who were cared for by two midwifery practices and delivered between January 1, 1998, and December 31, 2000. Cesarean delivery was significantly associated with the obese BMI (P < .001), nulliparity (P < .02), and newborn birth weight (P =.006). Prenatal weight gain did not have a significant correlation with cesarean birth (P = .24). In multivariable modeling, obese BMI, high newborn birth weight, nulliparity, and induction of labor increased the risk of cesarean birth. There was also a significant association between higher BMI and risk of induction of labor (P < .001). In a secondary analysis, obese BMI was associated with increased risk of induction in cases with ruptured membranes (OR 2.2; 95% CI 1.4-3.4) and postdates pregnancy (OR 2.0; 95% CI 1.1-3.4).

Obstet Gynecol. 2014 May;123 Suppl 1:172S. doi: 10.1097/01.AOG.0000447182.21511.09. Shoulder dystocia and labor induction stratified by maternal weight: to induce or not to induce? Sirota I1, Francis A, Chevalier M, Ashmead G. PMID: 24770084

...Retrospective study of all shoulder dystocia patients who delivered from 1998 to 2010, women in a control group without shoulder dystocia were matched two to one by maternal BMI, age, parity, and diabetic status...RESULTS: Included in the study was 57,259 deliveries; 144 shoulder dystocia cases and 288 women in the control group met study criteria. One hundred seven (74%) shoulder dystocia cases were induced or augmented; 37 (26%) labored spontaneously. One hundred thirty-six (47%) women in the control group were induced or augmented; 152 (53%) labored spontaneously... Across all BMIs, induced patients were 2.85 times more likely to have shoulder dystocia than noninduced patients (95% confidence interval 1.57-6.14; P<.001). After stratifying by BMI, induced normal-weight patients were 2.11 times more likely to have shoulder dystocia than spontaneously laboring normal-weight patients; induced or augmented overweight patients were 4.74 times more likely to have shoulder dystocia than their spontaneously laboring counterparts; and induced or augmented obese patients were 5.64 times more likely to have shoulder dystocia than their noninduced cohorts...CONCLUSION: Induction or augmentation appears to be associated with an increased shoulder dystocia risk with increasing maternal BMI.

Arch Dis Child Fetal Neonatal Ed. 2014 Jun;99 Suppl 1:A114-5. doi: 10.1136/archdischild-2014-306576.330. PLD.30 A 5-year review of maternal obesity and induction of labour on mode of delivery and risk of labour, anaesthetic and neonatal complications. Joannides C, Hon M, McGlone P, Parasuraman R, Al-Rawi S. PMID: 25020968

...Retrospective analysis of women with a booking BMI >45 between January 2009 and October 2013...RESULTS: 158 patients were analysed (mean BMI 49). 68% of all patients were either induced or required labour augmentation (background rate of 39%). 64% of these women achieved a vaginal delivery, increasing to 70% if no induction or augmentation. 71% of multiparous women who spontaneously laboured and had previously achieved a vaginal delivery, delivered vaginally again. Half of primiparous women requiring induction or labour augmentation had an emergency caesarean. 49% had intrapartum regional anaesthetic. 42% required multiple attempts, 19% needed an epidural re-site or spinal for theatre. CONCLUSION: These results mirror the UKOSS study findings. Higher maternal BMI is associated with an increased incidence of induction and augmentation of labour. Despite this the vaginal delivery rate is high. Primiparous women requiring induction or augmentation of labour were most susceptible to obstetric intervention....