A History of Cesarean Birth as a Risk Factor for Postpartum Hemorrhage Even After Successful Planned Vaginal Birth.

Background: It is unclear if a history of cesarean birth (CB) is a risk factor for postpartum hemorrhage (PPH) even after a successful planned vaginal birth.

Methods: A historical retrospective cohort study from all deliveries (42,456) between 2004 and 2019. Inclusion criteria were as follows: (i) women with only one previous CB; (ii) liveborn cephalic singleton pregnancy and term spontaneous labor; (iii) successful planned vaginal birth; (iv) no operative vaginal delivery; and (v) no history of PPH. Women who experienced intrapartum uterine rupture leading to CB were excluded. Those who experienced uterine rupture diagnosed after vaginal birth were not excluded. The labor after cesarean (LAC) group (109 women with previous CB and current vaginal birth) were compared with 2 control groups to consider the parity: control group 1 (1633 nulliparous women) and control group 2 (4197 parous women). The main outcome was the rate of PPH (> 500 mL). Multivariate analysis was performed to investigate whether previous CB was an independent risk factor for PPH. Bivariate analysis and causal framework was used to determine the relation between variables of clinical interest.

Results: The PPH rates in the LAC group, control group 1, and control group 2 were 12.8%, 5.3%, and 6.4%, respectively. Irrespective of the group control (1 or 2), a history of CB was associated with an increased risk of PPH: adjusted odds ratio (aOR) 2.38 [95% confidence interval (CI) 1.28-4.44] (adjusted with maternal age, overweight, hyperthermia, and use of oxytocin) and aOR 2.16 [95% CI 1.20-3.87] (adjusted with maternal age and overweight) for Groups 1 (parous) and 2 (nulliparous), respectively.

Conclusion: A history of cesarean birth could be a risk factor for PPH even after successful planned vaginal delivery.