EP19.05: Right occiput position, confirmed by ultrasound at the onset of spontaneous active labour is associated with an increased risk of operative deliveries

When studying spontaneous first labours using ultrasound it appeared that right occiput position might have a negative effect on labour outcomes. This had not been described in obstetric textbooks or in the scientific literature during the last century but there was a description of this in 19th century textbooks. We decided to study this specifically using ultrasound as an accurate means to confirm position. The study group consisted of nulliparous women in spontaneous labour with a single, cephalic fetus. When active labour was confirmed clinically, an examiner, not involved with the woman's clinical care, used transabdominal and transperineal ultrasound to accurately assess fetal head and spine position along with fetal head station using angle of progression and head-perineum distance measurements. Right positions were considered as ≥ 6 and <12 o'clock and left from 12 to <6. Labour outcomes were compared between the two groups. 164 women were examined, in 87 the fetal head entered the maternal pelvis on the left side and on the right in 77. At delivery only 3 babies were occiput posterior when the occiput had entered the pelvis on the left but 20 in the right sided group, p < 0.05. There were 13 operative deliveries in the left sided group and 30 on the right, p < 0.05. There were 10 instrumental deliveries in the left sided group and 22 when on the right, p < 0.05 There were 3 Caesareans in the left sided group and 8 on the right, this was non-significant. The fetal head enters the pelvis with the occiput on the left and right side with similar frequency, possibly favouring the left side slightly. When entering on the right the occiput is less likely to rotate to the anterior position leading to a higher risk of difficult deliveries including total operative and instrumental deliveries. This has not been described before in the scientific literature but may be of value in determining risk and when assessing abnormal labour progress.