(971) Rates of cesarean-delivery and perinatal outcomes in OA verses OP position by birth-weight in nulliparous

We aimed to evaluate how birth weight affects cesarean delivery rates and delivery outcomes for fetuses in occiput-anterior (OA) versus occiput-posterior (OP) positions. Specifically, we investigated whether the impact of fetal position on cesarean delivery varies with different birth weight categories and how it influences neonatal outcomes in nulliparous patients.

Study Design:

This was a retrospective cohort study of singleton, non-anomalous, term deliveries with vertex presentation in nulliparous individuals of California (2008-2020). Birth weight into eight categories: < 3500g, 3500-3749g, 3750g-3999g, 4000-4249g, 4250-4499g, 4500-4749g, 4750-4999g, ≥5000g. Multivariable Poisson regression model was used to examine the association of OP position and cesarean delivery along with outcomes (shoulder dystocia and scalp injury) for each weight category. Adjusted risk ratios (aRR) with 95% CI were estimated. 

Results:

In this study, we included 1,781,036 births of which 1.5% (n=26,943) were in OP position. Cesarean delivery rates were higher in OP  presented neonates in all birthweight categories, such as in < 3500 grams (77.6% vs 21.1%; aRR=3.50; 95% CI: 3.46-3.54), and ≥5000g (100% vs. 76.2%; aRR=1.29 (1.22-1.38)). Risk of shoulder dystocia was found to be increased in all most all birth weight categories in OP neonates, such as< 3500 g (0.92% vs 0.59%; aRR=1.51 (1.05-2.19)) and 3750-3999 g (6.25% vs 3.69%;aRR=1.72(1.23-2.39)). Risk of scalp injuries were found to be higher in OP neonates in birth weight categories such as < 3500 g (12.06 vs 4.69 aRR=2.53 (2.30-2.78)).

Conclusion:

We found that OP fetuses had a higher rate of cesarean delivery in all weight categories compared to OA. The difference between OA and OP cesarean delivery rates decreased as birth weight increased. In regards to perinatal outcomes we found OP neonates in most weight categories had higher rates of shoulder dystocia. Additionally scalp injury was increased in OP neonates compared to OA neonates.