Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. Prior preterm cesarean delivery was not associated with an increased risk of uterine rupture compared with prior term cesarean delivery during a subsequent trial of labor.

Evidence Level Rating: 2 (Good)

Uterine rupture is a feared obstetric emergency associated with substantial morbidity and mortality for both mother and fetus. It is well-established that the major risk factor for uterine rupture in high-income countries is scarring from previous uterine surgery, which became apparent after trial of labor after cesarean (TOLAC) increased in the early 1990s. The American College of Obstetricians and Gynecologists (ACOG) recommends that most women with one previous lower uterine segment cesarean can and should be offered TOLAC. That being said, there is a paucity of reliable data on the association specifically between preterm cesarean and risk of uterine rupture. This nationwide cohort study from Sweden included women with a first cesarean between 1983 and 2016 followed by a second TOLAC delivery between 1998 and 2016. In all, 9,300 women with a preterm cesarean and 57,168 women with a term cesarean had a subsequent TOLAC delivery and thus were eligible for analysis. It was found that uterine rupture occurred in 1.4% of women with a term cesarean and in 1.1% of women with a preterm cesarean, a relationship that was not significant after adjustment (aOR 0.94, 95% CI 0.74 to 1.18). These findings were consistent after stratifying preterm cesareans into subgroups based on gestational age at delivery (i.e. between 32+0 and 36+6 gestational weeks and < 32+0 gestational weeks). However, preterm cesarean was found to be associated with a significantly increased risk of placenta abruptio after adjusting for confounders like placenta abruptio during the exposure delivery and pre-eclampsia during the outcome delivery (aOR 1.40, 95% CI 1.13 to 1.93). These findings are in conflict with previously published reports; however, the large sample size and prospective study design lend credence to these data. In conclusion, this study suggests that among candidates for TOLAC, gestational age at prior cesarean need not be included in risk assessment as preterm cesarean was shown to not be associated with an increased risk of uterine rupture in subsequent TOLAC.

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