Sonographic assessment of fetal spine and head position during the first and second stages of labor for the diagnosis of persistent occiput posterior position: a pilot study

OBJECTIVES:The aim of this pilot study was to perform a preliminary investigation into the predictive values of the position of the fetal spine and of the occiput measured during the first and second stages of labor by intrapartum ultrasound for persistent occiput posterior (OP) position.METHODS:This was a prospective, cohort study, in which 100 women with singleton pregnancies were enrolled during the first or second stage of labor. The women underwent intrapartum transabdominal sonography and the positions of the fetal head and spine were recorded. The women were followed up until delivery and occiput position at birth was assessed.RESULTS:Eighty-four pregnancies were evaluated in the second stage of labor, with 74 of these also evaluated in the first stage. Fifty-one percent of fetuses were found to be in an OP position during the first stage of labor, but the majority of these rotated to an anterior position before delivery. There were six cases of OP at delivery, and all of these were among the 23 fetuses that were found to be in an OP position on ultrasound evaluation during the second stage of labor. All six were also found to have a posterior spine position during the second stage of labor, with this finding observed in only one fetus with occiput anterior position at delivery.CONCLUSIONS:The results of this study suggest that the position of the head and spine during the second stage of labor could be useful indicators for predicting the OP position at delivery. The results also suggest that the OP position at delivery results from a failure of rotation from the OP position, rather than a malrotation from the anterior position. Studies with larger sample sizes are needed to confirm these results.