(159) Primipara with cesarean history: Impact of gestational age at term on mode of delivery

Objective: To assess the risk of cesarean delivery (CD) for each week of gestation (WG) of ongoing pregnancy (OP) in primipara at term with a prior CD.

Study Design: Secondary analysis of the randomized Lower Uterine Segment Trial. All included women were eligible for a trial of labor. From the start of term and at the start of each subsequent week of completed gestation, OP was defined as that of a woman who was still pregnant and who gave birth at any time after that date. For each WG for these OP, the CD rate was defined as the number of CDs performed in each OP group divided by the number of women in this group. Separate models for each WG, adjusted by maternal characteristics and hospital status, were used to compare the CD risk between OP and those delivered in the preceding week. The same methodology was applied in a subgroup of women with induction of labor (IoL). Odds ratios were calculated after adjusting for center,BMI, diabetes, hypertensive disorders, and macrosomia.

Results: Among the 2,339 included primipara at term, 1834 (78.4%) finally had a trial of labor including 390 (16.6%) IoL. The overall CD rate was 44.2% (n=1,034). This rate was 44.3% (n=173) in the 390 women with IoL. These rates remained stable for OP from 37 0/7 to 40 0/7 WG and increased at 41 0/7 WG (Table 1). In both univariate and multivariate analyses, OP at or beyond 41 0/7 WG was associated with a higher risk of CD than pregnancy delivered the previous week (ORa = 2.13 (95% CI [ 1.65-2.75]). In contrast, at each gestational week, the CD rate after IoL was not significantly different between OP and pregnancy delivered the previous week, even at or beyond 41 0/7 WG (Table 2).

Conclusion: The overall CD rate for OP in primipara with a previous CD only increases from 41 0/7 weeks. Among women delivered after IoL, there was no significant difference in CD rates for OPs compared with those for women who gave birth in the preceding WG.