Previous preterm cesarean delivery and risk of uterine rupture in subsequent trial of labor-a national cohort study

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. However, the proposed association has only been investigated in a few studies and never in a study based on unselected contemporary prospectively collected data. OBJECTIVE: This study aimed to investigate the risk of uterine rupture among women attempting trial of labor after 1 previous preterm cesarean delivery compared with women with 1 previous term cesarean delivery. STUDY DESIGN: In this population-based cohort study, we used the Swedish Medical Birth Register between 1983 and 2016 and identified 9300 women with 1 previous preterm index cesarean delivery, 57,168 women with 1 previous term index cesarean delivery, and a second outcome delivery defined as trial of labor after 1 previous cesarean delivery. The risk of the main outcome uterine rupture and secondary out-comes placental abruption; placenta accreta spectrum; postpartum hemorrhage; blood transfusion; appearance, pulse, grimace, activity, and respiration of <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 delivery, 102 (1.1%) had uterine rupture in the outcome delivery compared with 759 of women (1.4%) with term index cesarean delivery. This corresponded to a decreased risk of uterine rupture for women with preterm index cesarean delivery (odds ratio, 0.79; 95% confidence interval, 0.64-0.97), which did not remain significant in the analysis adjusted for maternal age, interdelivery interval, maternal body mass index, maternal height, induction of labor, postoperative infection after index cesarean delivery, and birthweight (odds ratio, 0.94; 95% confidence interval, 0.74-1.18). Stratifying by gestational week at index cesarean delivery (32+0 to 36+6 and <32+0 weeks' gestation) did not alter the main result. Stratifying by interdelivery interval revealed that women with a preterm index cesarean delivery were at a decreased risk of uterine rupture (odds ratio, 0.55 [95% confidence interval, 0.39-0.78]; adjusted odds ratio, 0.74 [95% confidence interval, 0.51-1.07]) in interdelivery intervals of >36 months whereas there were no significant differences within other time intervals. Of the secondary outcomes, 89 women (1.0%) with preterm index cesarean delivery were diagnosed as having placental abruption compared with 331 women (0.6%) with term index cesarean delivery, which corresponded to an approximately 60% increased risk (odds ratio, 1.66; 95% confidence interval, 1.31-2.10), which remained significant after adjusting for confounders (odds ratio, 1.49; 95% confidence interval, 1.13-1.96). Likewise, there was a slightly increased risk of postpartum hemorrhage for women with preterm index cesarean delivery (adjusted odds ratio, 1.12; 95% confidence interval, 1.02-1.24). There were no significant differences in the remaining secondary outcomes. CONCLUSION: The findings of this study suggest that preterm cesarean delivery is not associated with an increased risk of uterine rupture. Hence, women with 1 previous preterm cesarean delivery (with lower uterine segment incision) should receive medical management and counseling similar to women with previous term cesarean delivery before trial of labor after cesarean delivery.