Occipitoposterior position: associated factors and obstetric outcome in nulliparas.

OBJECTIVE: To determine factors associated with term delivery in the occipitoposterior position and examine obstetric outcomes from that delivery position in nulliparas.
METHODS: We did a retrospective analysis of population-based data of 16,781 nulliparas who delivered at term (37-42 weeks) with singleton, cephalic presentations. Factors examined for possible association with occipitoposterior position were fetal weight, maternal age, completed weeks of gestation, epidural analgesia in labor, labor induction, and oxytocin augmentation. Obstetric outcome measures were mode of delivery and percentage of infants with Apgar scores less than 8 at 5 minutes.
RESULTS: The frequency of occipitoposterior position was 4. 6%. Fetal weight, epidural analgesia, and oxytocin augmentation were strongly associated with delivery in the occipitoposterior position (odds ratios 1.18, 2.21, 1.44, respectively, P <.001, logistic regression). There was a higher incidence of instrument and emergency cesarean deliveries in occipitoposterior compared with occipitoanterior labors (43.7% versus 24.4%, 41.7% versus 13.7%, respectively, P <.001, the chi(2) test). There was no significant difference in percentage of infants with low Apgar scores at 5 minutes between those who delivered occipitoposterior or occipitoanterior.
CONCLUSION: Epidural analgesia and oxytocin augmentation are associated with increased incidence of occipitoposterior position, which leads to increased operative obstetric intervention for delivery.