The effect of polyhydramnios on the success of trial of labor after cesarean delivery (TOLAC): A retrospective cohort

Objective: Prediction of success of trial of labor after cesarean delivery (TOLAC) is of major importance. We investigated the impact of polyhydramnios on the success rate of TOLAC.

Study design: A retrospective cohort study of all women with singleton pregnancies ≥ 34th weeks of gestation who underwent TOLAC after one previous cesarean delivery, between 2011 and 2016 in a single tertiary care center. Polyhydramnios was defined as amniotic fluid index ≥ 240 mm. Primary outcome was defined as the rate of successful TOLAC.

Results: 31,245 women gave birth during the study period, of them 1637 (5.3 %) women underwent TOLAC and met inclusion criteria. 39 (2.4 %) women with polyhydramnios were compared to a control group of 1598 (97.6 %) women with amniotic fluid index < 240 mm. Polyhydramnios significantly reduced the rate of successful TOLAC: 69.2 % (27/39) in the study group compared to 85.8 % (1371/1598) in the control group (P = 0.009). In a subgroup analysis based on amniotic fluid index, women with AFI > 270 mm had substantially lower TOLAC success rate [9/19 (47.4 %) vs 18/20 (90 %); P = 0.006]. There was no difference in the rate of uterine rupture between the groups (0/39 (o%) vs 9/1598 (0.56 %); P = 0.64). Logistic regression analysis revealed that polyhydramnios remained significantly associated with higher rates of cesarean delivery [OR 3.09 (95 % CI, 1.37-6.98)] after adjustment for confounding factors.

Conclusion: Polyhydramnios was associated with significantly reduced TOLAC success rate with no statistical difference in the rate of uterine rupture. This information should be considered in physician counseling.