Prediction of persistent occiput posterior position by sonographic assessment of fetal head attitude at start of second stage of labor: prospective study

Abstract

ObjectivesTo evaluate the relationship between the flexion of the fetal head quantified by means of the chin‐to‐chest angle (CCA) in fetuses in OP position at the beginning of the second stage of labor, and persistent OP position at birth.MethodsSingle‐center, prospective, observational study conducted at the University Hospital of Parma, Italy. We included singleton pregnancies at term with fetuses in OP position at the beginning of the second stage of labor. The fetal head position, station by means of angle of progression and head‐to‐perineum distance; and attitude by means of CCA were assessed using transabdominal or transperineal ultrasound. The primary outcome of the study was the occurrence of persistent OP position at birth, including spontaneous or operative (abdominal or vaginal) delivery.ResultsBetween January 2022 and July 2022, 76 women were included in the study. There were 48 (63.2%) spontaneous rotations of the fetal head, and in all spontaneous vaginal delivery occurred. Among the 28 (36.8%) fetuses that did not rotate spontaneously into an OA position, eight (28.6%) had a spontaneous vaginal delivery while assisted vaginal birth and cesarean delivery were performed in 11 (39.3%) and 9 (32.1%) cases respectively. Multivariable logistic regression analysis showed that the CCA (aOR 2.15, 95% CI 1.22 – 3.78; P=0.008) and nulliparity (aOR 0.20, 95% CI 0.06 – 0.76; P=0.02) were independently associated with persistent OP position at birth. Moreover, the CCA showed an AUC of 0.69 (95% CI 0.56 – 0.82, p=0.005) for the prediction of persistent OP position. The optimal cut‐off value of the CCA was 36.5 degrees, and was associated with 0.82 (95% CI 0.63 – 0.94) sensitivity, 0.50 (95% CI 0.35 – 0.65) specificity, 0.49 (95% CI 0.34 – 0.64) positive predictive value, 0.83 (95% CI 0.64 – 0.94) negative predictive value, 1.64 (95% CI 1.18 – 2.29) positive likelihood ratio, and 0.36 (95% CI 0.15 – 0.83) negative likelihood ratio.ConclusionsOur data shows that within a population of women with fetal OP position at the beginning of the second stage of labor the sonographic fetal attitude measured by means of the CCA might help in the identification of fetuses at risk of persistent OP position. Such findings can be useful for patient counselling when OP position is diagnosed at full cervical dilatation. Further studies should investigate if the CCA might select patients who may benefit from manual rotation of the fetal head.This article is protected by copyright. All rights reserved.