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28: Duration of 2nd stage of labor induction and maternal/perinatal outcomes in full-term low-risk nulliparas

      Objective

      Allowing a longer second stage (SS) increases the number of vaginal deliveries (VD) but women with longer SS are more likely to have a cesarean delivery (CD) and adverse maternal/perinatal outcomes than those with shorter SS. We sought to quantify the association of the duration of SS with CD and maternal/perinatal morbidity in a contemporary cohort of low-risk nulliparas who underwent induction of labor (IOL) at full term (FT).

      Study Design

      Planned secondary analysis of a multicenter RCT of IOL at 39 wks vs. EM until at least 405/7 wks but no later than 422/7 in low-risk nulliparas with singleton gestations from ′14-′17. Those with viable non-anomalous neonates who underwent IOL with oxytocin were included in this analysis regardless of study arm and receipt of cervical ripening. Duration of SS (defined as time from complete dilation to delivery) was examined by 1-hr intervals from <2 to ≥5 hrs in relation to CD, as well as to both a maternal and perinatal composite of adverse outcomes. Categorical variables including epidural use were compared using Cochrane-Armitage trend or Chi-Square tests, and continuous variables using the Jonckheere-Terpstra test of trend. Poisson regression was used for multivariable adjustments and to test for variation by use or not of epidural.

      Results

      Of 3058 eligible women who underwent IOL, 2431 had information on duration of SS: the median duration of SS was 1.2 hrs (IQR 0.6-2.3), with 69% lasting <2 hrs, 15% 2-2.9 hrs, 8.2% 3-3.9 hrs and 7.7% ≥5 hrs (Table 1). Overall 79% had an epidural. Mean BMI but not presence of a modified Bishop score <5 or epidural use was associated with SS duration. The frequencies of CD and the maternal and perinatal composites all increased with increasing SS duration (Table 1); still most women delivered vaginally even with SS duration ≥4-5hrs. After multivariable adjustment (Table 2), longer SS durations (compared to <2 hrs) were associated with increases up to 45 times for CD but only up to 2.2-2.4 times for the maternal and perinatal composites (Table 2). The strength of the associations appeared to be greatest after 3 hrs. Findings were not modified by epidural use (all p-values for interaction >0.48).

      Conclusion

      In contemporary low-risk nulliparas who underwent IOL at FT, risk for CD increases markedly with SS duration but out of proportion to maternal and perinatal morbidity; most women deliver vaginally even after 3 hrs. Findings did not differ by epidural use. These data are valuable for counseling about a protracted SS.
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