Labor and delivery outcomes by delivery method in term deliveries in occiput posterior position: a population-based retrospective cohort study

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Occiput posterior is the most common malposition in labor. Deliveries in occiput posterior position have been shown to have higher rates of adverse short-term maternal and neonatal outcomes compared with deliveries in occiput anterior position. There are no guidelines providing recommendations nor summarizing risks of adverse outcomes by delivery method to inform the decision-making process in occiput posterior delivery management. Population-based studies examining the outcomes associated with various management processes of occiput posterior position at the time of labor or delivery are lacking. This study aimed to describe the current management of term singleton occiput posterior deliveries in British Columbia, Canada and to examine the association between different management strategies and adverse outcomes by describing the rates of: occiput posterior malposition; and spontaneous vaginal delivery, operative vaginal delivery, and cesarean delivery from occiput posterior malposition. We also analyzed the rates of adverse labor and delivery outcomes stratified by fetal position and delivery mode, and the interaction effect of occiput posterior position and delivery mode on the rates of adverse outcomes. This was a retrospective cohort study of cephalic term singleton deliveries in British Columbia from 2004 to 2020, using the British Columbia Perinatal Data Registry. The obstetrical adverse outcome index (a composite of 10 adverse maternal or neonatal events), adverse outcome index subcomponent rates, and adverse outcome index-derived weighted scores were compared between deliveries stratified by fetal position at delivery (occiput posterior or occiput anterior) and occiput posterior deliveries stratified by delivery method. Multivariable log-binomial logistic regression was used to model the adverse outcome index score. Of 306,237 term births, 19% had occiput posterior position during labor, 37% of which persisted in occiput posterior position at delivery. Among occiput posterior deliveries, 27% were spontaneous vaginal deliveries, 8% vacuum, 5% forceps, 1% mixed vacuum-forceps, and 59% were cesarean delivery; this distribution differed from that of occiput anterior deliveries (P<.0001). Overall, adverse outcome index scores were significantly higher in persistent occiput posterior deliveries (8.8% had ≥1 adverse outcomes; adjusted rate ratio, 1.07 [1.01-1.14]) than in occiput posterior labors that rotated to occiput anterior deliveries; the most frequent adverse outcome was third- or fourth-degree lacerations. Neonatal adverse outcomes were also more frequent in occiput posterior delivery (4.3% vs 3.3%; adjusted rate ratio, 1.21 [1.10-1.35]), whereas maternal outcomes were similar between groups (4.8% vs 6.0%; adjusted rate ratio, 1.04 [0.96-1.13]). Among persistent occiput posterior deliveries, spontaneous vaginal delivery and cesarean delivery had the lowest proportion of deliveries with ≥1 adverse outcomes (6.1% and 6.2%), whereas forceps deliveries had the highest (38.1%); the largest contributor to the adverse outcomes were third- or fourth-degree lacerations. Among occiput posterior deliveries with any adverse outcome, cesarean delivery had the highest Severity Index score, due in part to the inclusion of third- or fourth-degree tears (which are assigned a comparatively low score) as the most common adverse event in the other vaginal delivery modes, and because of outcomes with a higher severity score being associated with cesarean delivery, such as uterine rupture (a reason for cesarean delivery) and intensive care unit admission (an outcome following cesarean delivery). Overall, in a multivariable regression model, delivery mode and the interaction between delivery mode and occiput posterior position were significant predictors of a delivery with ≥1 adverse outcomes, whereas occiput posterior position itself was not. One in five singleton deliveries at term gestation had occiput posterior position in labor; most of these rotated to occiput anterior by delivery, which had better outcomes than persistent occiput posterior deliveries. Among the latter, spontaneous vaginal delivery and cesarean delivery had the lowest frequency of adverse outcomes, whereas forceps deliveries had the highest. This study provides a robust updated analysis of birth outcomes following different occiput posterior management strategies, which can inform provider decision-making and counseling. Its observational design may limit its use for direct recommendations for management of occiput posterior malposition, yet the study helps to define the risks associated with different modes of delivery in the setting of occiput posterior malposition. With additional studies examining success rates of intermediate occiput posterior-occiput anterior rotation, other delivery management steps, and long-term outcomes, this study helps to define safe management of occiput posterior delivery.