Does elective IOL at 39 weeks increase c-section risk?

ACOG and OBGYNs everywhere have made a big push to reduce complications and prematurity by postponing elective inductions of labor (IOL) until 39 weeks. An elective induction of labor is when an OB tries to get a woman into labor for social reasons. Maybe she has a limited window when she can get time off of work, or when she can get help with childcare, or just wants the baby to be born in a certain month. Sometimes the mom is just plain tired of being pregnant. An “elective” IOL is very different from a “medically indicated” IOL. For a medically indicated IOL, the risks to the mother or fetus are higher if she remains pregnant than if the baby is born. For instance, when a woman develops severe preeclampsia or the pregnancy goes past 41 weeks, the obstetrician will recommend an IOL because it’s safer for the baby to be born.

The reasons for an elective IOL vary and are very individual. Not long ago, doctors would offer an induction of labor before 39 weeks, sometimes even before the baby was term or 37 weeks. We now know that it’s much better for infants if we wait until at least 39 weeks for an elective IOL. But, it’s still very controversial whether a woman undergoing an elective IOL at 39 weeks has an increased risk of c-section versus waiting until she goes into labor on her own. The prior research is hard to apply to first time moms. Studies that simply looked back at old data (observational studies) did not show a difference in the c-section rate for elective IOL versus expectant management. Unfortunately, the control group in this case doesn’t match true life. The authors are looking at women who underwent elective IOLs versus women who went into spontaneous labor. In real life, lots of women who don’t want an IOL and want to go into spontaneous labor end up needing an IOL anyway. This muddies the water in the observational studies, which don’t factor in women who desired a spontaneous labor but needed an IOL. Prior randomized controlled trials showed a 20% lower c-section rate for elective IOL compared with expectant management. Unfortunately, only 10% of the women included were first time moms.

In the December 2015 Green Journal, Dr. Miller and his colleagues conducted a randomized controlled trial to compare the c-section rate for first time moms with unfavorable cervixes at 39 weeks gestation who get an elective IOL versus those who don’t. An unfavorable cervix means that the cervix is not showing signs of being ready for labor. Providers make this determination by calculating the Bishop Score, which takes into account a variety of factors like how dilated the cervix is and how long it is. This study only included women with a Bishop Score of 5 or less, meaning the cervix was “unfavorable.” By including only first time moms with a low Bishop Score, the authors were isolating a population of women at high risk of needing a c-section after an elective IOL.

The results were just shy of being statistically significant because there were not quite enough women enrolled in the study- 162. Women who were randomly assigned to have an elective IOL at 39 weeks had a 30.5% c-section rate. Women who were randomly assigned not to have an elective IOL had a 17.7% c-section rate. This is quite a difference! But just not “statistically significant.” Now, not all the women who didn’t get an elective IOL ended up in spontaneous labor. 44% were admitted in spontaneous labor. Others ended up needing a medically indicated IOL for complications like high blood pressure, the bag of water breaking before labor started, and pregnancy going past 41 weeks. More women who waited to go into labor developed a hypertensive disorder, likely because they were pregnant longer. Women who had an elective IOL spent about 10 hours longer on the Labor and Delivery unit.

Although the results were not statistically significantly different, the difference is quite impressive! A larger study is needed to discover if the difference will hold up and become significant, but this study would certainly make me think twice if I were a first time mom at 39 weeks with an unfavorable cervix considering an elective IOL.