Investigation of occiput posterior delivery by intrapartum sonography.

OBJECTIVE To investigate if occiput posterior delivery is the consequence of persistence of an initial occiput posterior position or malrotation from an initial occiput anterior or transverse position. METHODS This was a cross-sectional study involving transabdominal sonography to determine fetal occipital position in 918 singleton pregnancies with cephalic presentation in active labor at 37-42 weeks of gestation. The relationship between occipital position in labor and at delivery was examined. RESULTS The occiput was posterior in 33.0% (149/452), 33.9% (101/298) and 19.0% (32/168) of fetuses at the respective cervical dilatations of 3-5, 6-9 and 10 cm and this persisted at delivery in 21.5% (32/149), 31.7% (32/101) and 43.8% (14/32) of cases. In 70% (32/46), 91% (32/35) and 100% (14/14) of occiput posterior deliveries there was persistence from this position at 3-5, 6-9 and 10 cm of cervical dilation. CONCLUSIONS The majority of occiput posterior positions during labor rotate to the anterior position even at 10 cm of cervical dilatation. However, the vast majority of occiput posterior positions at delivery are a consequence of persistence of this position during labor rather than malrotation from an initial occiput anterior or transverse position.