SAN DIEGO – The risk of C-section doubled in women undergoing induction of labor who received an epidural before 4 -cm dilation, compared with later epidural administration, a retrospective study found.
In 281 singleton pregnancies at gestational ages greater than 36 weeks that underwent induction of labor from 2008 to 2009 at one institution, 83% of mothers received an epidural. The C-section rate was significantly higher among the 233 women who received an epidural, compared with the 48 women who did not get an epidural – 30% vs. 8%.
In unadjusted results for women who got an epidural, "early" administration before 4-cm dilation was associated with a 38% chance of C-section, compared with a 24% C-section rate with "late" epidural administration when dilation reached at least 4 cm, Monica Rincon and her associates reported at the annual meeting of the American College of Obstetricians and Gynecologists.
After adjusting for the effects of age, race, body mass index (BMI), parity, and Bishop score, the risk for C-section was doubled with early vs. late epidural, said Ms. Rincon, a senior research assistant in the women’s health research unit at Oregon Health and Science University, Portland.
A non-reassuring fetal heart tracing was significantly more likely to be an indication for C-section in the early epidural group (18%), compared with the late epidural group (9%). Arrest of labor was the indication for C-section in 25% of the early epidural group and 21% of the late epidural group, which was not a statistically significant difference, she said.
Women in the early epidural group were significantly more likely to be white (80%), compared with the late epidural group (66%).
Several other factors besides timing of the epidural were associated with significantly increased risk for C-section after adjusting for confounders. The risk doubled with a Bishop score less than 5 at the time of admission, compared with higher Bishop scores. Maternal age of at least 35 years tripled the risk for C-section, compared with younger age. The risk for C-section quadrupled with a body mass index of at least 30 kg/m2, compared with lower BMI. Nonwhite women had a fivefold increased risk for C-section, compared with white women. Nulliparous women had a 13-fold increased risk for C-section, compared with multiparous women.
The early and late epidural groups did not differ significantly by age, BMI, gestational age, birth weight, reason for induction of labor, or the proportions of women who were nulliparous or who had a Bishop score greater than 5 at admission.
Among all 281 deliveries (including those without an epidural), 68% were spontaneous vaginal deliveries, 6% were assisted vaginal deliveries, 8% were C-sections for non-reassuring fetal heart tracings, and 18% were C-sections because of arrest of labor.
Approximately 22% of U.S. labors in 2006 were induced, Ms. Rincon said. Previous studies of nulliparous women have shown a higher rate of C-section after labor induction, compared with spontaneous labor. Studies of multiparous women with induced labor provide conflicting results for the risk of C-section, with some reporting no increase in risk of C-section and others reporting increased C-section rates.
Among 2,231 deliveries in 2011 at Oregon Health and Science University, 41% involved labor induction, 56% used an epidural, and 27% were C-section deliveries, she said.
The current study excluded twin deliveries, vaginal births after C-section deliveries, and patients whose epidural status was unknown.
Ms. Rincon reported having no financial disclosures.