Comparison of transvaginal digital examination with intrapartum sonography to determine fetal head position before instrumental delivery.

OBJECTIVE To investigate the accuracy of intrapartum transvaginal digital examination in defining the position of the fetal head before instrumental delivery. PATIENTS AND METHODS In 64 singleton pregnancies undergoing instrumental delivery the fetal head position was determined by transvaginal digital examination by the attending obstetrician. Immediately after or before the clinical examination, the fetal head position was determined by transabdominal ultrasound by a trained sonographer who was not aware of the clinical findings. The digital examination was considered to be correct if the fetal head position was within +/- 45 degrees of the ultrasound finding. The accuracy of the digital examination was examined in relation to maternal and fetal characteristics. RESULTS Digital examination failed to define the correct fetal head position in 17 (26.6%) cases. In 12 of 17 (70.6%) errors the difference was >/= 90 degrees and in five (29.4%) the difference was between 45 degrees and 90 degrees. The accuracy of vaginal digital examination was 83% for occiput-anterior and 54% for occiput-lateral + occiput-posterior positions. Logistic regression analysis demonstrated significant independent contributions in explaining the variance in the accuracy of vaginal examination for the station of the fetal head, the position of the fetal head and the experience of the examining obstetrician. CONCLUSIONS Digital examination during instrumental delivery fails to identify the correct fetal head position in about one quarter of cases.