EP25.20: Fetal back position at first stage can predict malpresentation in 2nd stage in neuraxial analgesia labour

It has been reported malpresentation are increased during neuraxial analgesia labour. The aim of this study is to make it clear whether fetal back position affect delivery outcome in primiparous underwent neuraxial analgesia or not. The primiparous cases of deliveries with neuraxial analgesia between September 2018 and October 2022 were included in this retrospective study. The position of the fetal back before induction of anesthesia was confirmed by transabdominal ultrasound scan, and the cases were classified into two groups: the BP (back posterior) group (cases with the fetal back at 3.5 to 8.5 hours): 34 cases, and the non-BP group (cases with the fetal back at 8.5 to 3.5 hours): 115 cases. And the outcome of delivery were investigated. The cases in which the midline angle was 45 degrees or more with transperineal ultrasound examination were diagnosed as malpresentation at the time of the cervix full opened and digital rotation was performed to fix the malpresentation. 149 cases were included in the study. There were no significant differences in maternal background in BP and non-BP group. The incidence of malpresentation was significantly higher in the BP group (p = 0.02): 15/115 (13.0%) in the non-BP group vs. 11/34 (32.4%). There were no significant incidence differences in delivery arrest, instrumental delivery and Caesarean section, (non-BP group vs. BP group: 37.4% vs. 29.4%, 44.3% vs. 41.18%, 27.8% vs. 23.5%), respectively. Although the frequency of fetal malpresentation during the second stage of delivery increased when the fetal back was positioned dorsal to the mother during induction of anesthesia, it did not affect the outcome of delivery. The digital rotation for cases with fetal malrotation in the second stage of delivery may have had an effect. Confirmation of fetal position in the first stage of delivery to predict abnormalities of rotation is meaningful for these cases, because abnormalities of rotation can cause delivery termination or obstetric surgery.