Transactions of the Twenty-Sixth Annual Meeting of the Society for Maternal-Fetal Medicine
Induction of labor and cesarean delivery by gestational age

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Objective

Studies of cesarean delivery (CD) rates among women undergoing induction of labor (IOL) often compare such women to women experiencing spontaneous labor at similar gestational ages. We sought to examine the association between IOL at various gestational ages and CD, accounting for the effect of increased gestational age among the comparison group who were managed expectantly.

Study design

We conducted a retrospective cohort study of all term, singleton, cephalic presentation pregnancies delivered at our institution over 15 years excluding cesarean deliveries before labor. For each gestational age of induction, we created a comparison group of women who were undelivered at that gestational age, and who experienced labor at some future gestational age.

Results

In women undergoing IOL at 38 weeks gestation, the CD rate was 11.9% as compared to 13.3% (P = .42) of women beyond 38 weeks gestation. The CD rate for induction of labor compared to ongoing pregnancy was 14.3% versus 15.0% (P = .62) at 39 weeks, 20.4% versus 19.0% (P = .41) at 40 weeks, and 24.3% versus 26.0% (P = .39) at 41 weeks. When controlling for potential confounding, there was a higher rate of CD among women with expectant management beyond 38 weeks (adjusted odds ratio [AOR] 1.80; 95% CI 1.29-2.53), 39 weeks (1.39; 95% CI 1.08-1.80), and 40 weeks (AOR 1.27; 95% CI 1.00-1.62).

Conclusion

Our findings suggest that IOL may not increase a woman's risk of CD when compared to expectant management. While this question has been addressed prospectively at 41 weeks gestation, it requires further examination at earlier gestations and among various subgroups.

Section snippets

Material and methods

We conducted a retrospective cohort study of all term, singleton, cephalic deliveries at the University of California, San Francisco (UCSF) from 1986 to 2001. Women with a previous cesarean or who experienced a cesarean in the current pregnancy without labor or for an indication other than dystocia or nonreassuring fetal assessment (eg, placenta previa, breech, HSV) were excluded. Because elective induction was not the practice at the institution, we did not exclude high-risk patients with

Results

During the study period, 19,377 women met study inclusion criteria. Of these, 2,932 (15.1%) underwent induction of labor and 16,445 (84.9%) experienced spontaneous onset of labor. The two groups differed by every characteristic considered as a potential confounder except for level of education (Table I). Overall, the cesarean delivery rate among the women who were induced was 20.6% as compared to 10.9% among those with spontaneous labor (P < .001).

In the comparison that is commonly made, when

Comment

Consistent with the existing literature, we found that both overall and when compared to women of the same gestational age, women undergoing induction of labor had a higher cesarean delivery rate than women in spontaneous labor. However, both overall and particularly among nulliparas, there was generally a lower cesarean delivery rate among women who were induced as compared to those managed expectantly who delivered at greater gestational ages.

The latter finding is in stark contrast to most

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Dr Caughey is supported by the National Institute of Child Health and Human Development, grant # HD01262 as a Women's Reproductive Health Research Scholar.

Presented at the Twenty-Sixth Annual Meeting of the Society for Maternal Fetal Medicine, Miami, FL, January 30-February 4, 2006.

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