PREVIOUS PRETERM CESAREAN DELIVERY AND RISK OF UTERINE RUPTURE IN SUBSEQUENT TRIAL OF LABOR

Background: Previous cesarean delivery is the major risk factor for uterine rupture in subsequent trial of labor. It has been suggested that a previous preterm cesarean delivery is associated with an increased risk of uterine rupture compared with a previous term cesarean delivery. Yet, the proposed association has only been investigated in a few studies and never in a study based on unselected contemporary prospectively collected data.

Objectives: To investigate the risk of uterine rupture among women attempting trial of labor after one previous preterm cesarean compared with women with one previous term cesarean.

Study design: In this population-based cohort study we used the Swedish Medical Birth Register between 1983 and 2016 and identified 9300 women with one previous preterm index-cesarean, 57 168 women with one previous term index-cesarean and a second outcome-delivery defined as trial of labor after one previous cesarean delivery. The risk of the main outcome uterine rupture and secondary outcomes placenta abruptio, placenta accreta spectrum, postpartum hemorrhage, blood transfusion, Apgar <7 at 5 minutes, neonatal cerebral dysfunction and neonatal seizures were assessed using multivariate logistic regression models adjusted for potential confounders.

Results: Among women with a preterm index-cesarean, 102 (1.1%) suffered from uterine rupture in the outcome-delivery compared with 759 (1.4%) of women with term index-cesarean. This corresponded to a decreased risk of uterine rupture for women with preterm-index cesarean (OR 0.79 [95% CI 0.64-0.97), which did not remain significant in analysis adjusted for maternal age, inter-delivery interval, maternal BMI, maternal height, induction of labor, postoperative infection after index-cesarean and birthweight (OR 0.94 [95% CI 0.74-1.18]). Stratifying by gestational week at index-cesarean (32+0-36+6 and <32+0 gestational weeks) did not alter the main result. Stratifying by inter-delivery interval revealed that women with a preterm index-cesarean were at decreased risk of uterine rupture (OR 0.55 [95% CI 0.39-0.78]; Adjusted OR 0.74 [95% CI 0.51-1.07]) in inter-delivery intervals longer than 36 months whereas there were no significant differences within other time intervals. Of secondary outcomes, 89 (1.0%) of women with preterm index-cesarean were diagnosed with placenta abruptio compared with 331 (0.6%) of women with term index-cesarean, which corresponded to an approximately 60% increased risk (OR 1.66 [95% CI 1.31-2.10]), which remained significant after adjusting for confounders (OR 1.49 [95% CI 1.13-1.96]). Likewise, there was a slightly increased risk of postpartum hemorrhage for women with preterm index-cesarean (Adjusted OR 1.12 [95% CI 1.02-1.24]). There were no significant differences in remaining secondary outcomes.

Conclusion: The findings of this study suggest that preterm cesarean is not associated with an increased risk of uterine rupture. Hence, women with one prior preterm cesarean (with lower uterine segment incision) should receive medical management and counselling similar to women with prior term cesarean prior to trial of labor after cesarean.

Keywords: Uterine rupture; cesarean delivery; epidemiology; preterm; risk factors.