The association between gestational age and maternal adverse outcomes in patients undergoing trial of labor after cesarean.

Background: Although successful trial of labor after cesarean (TOLAC) resulting in vaginal birth after cesarean (VBAC) can lead to improved maternal and neonatal outcomes, an unsuccessful TOLAC is associated with increased risk of uterine rupture, higher blood loss, and increased risk of infection. Data remain limited in terms of whether differences in gestational age of patients who attempt TOLAC affect maternal morbidity. The aim of this study was to examine the association between gestational age and maternal adverse outcomes in women undergoing trial of labor after cesarean.

Methods: This population-based cross-sectional study used birth data from the U.S. National Vital Statistics from 2014 to 2018. Women with liveborn singleton gestation who underwent TOLAC at 23-41 weeks' gestation were included in the analytic population. The primary outcome was a composite of maternal adverse outcomes: admission to the Intensive Care Unit, blood transfusion, uterine rupture, or unplanned hysterectomy. Secondary outcomes were individual measures within the primary composite outcome. Outcomes were compared between patients who underwent TOLAC at term (37-41 weeks gestational age) and those who underwent TOLAC at preterm (23-36 weeks gestational age). Multivariable analyses were adjusted for demographic and obstetric differences between the two groups.

Results: 455,284 patients met inclusion criteria for the study; 39,589 (8.7%) were at a preterm gestational age (GA) and 415,695 (91.3%) were at a term GA. The overall composite maternal adverse outcome was significantly higher for patients undergoing TOLAC at preterm GA (12.0 per 1000 live births) compared to term GA (8.0 per 1000 live births; aRR=1.42; 95% CI: 1.29-1.56). Among individual conditions within the primary composite outcome, preterm gestational age was associated with increased risk of admission to the Intensive Care Unit, blood transfusion, and unplanned hysterectomy.

Conclusions: In patients who underwent TOLAC, preterm gestational age was associated with increased risk of adverse maternal outcomes.