EP19.03: Narrower subpubic arch angle is associated with breech presentation in nulliparous women at term

The aim of the present study was to evaluate the correlation between subpubic arch angle (SPA) and fetal breech presentation in nulliparous women at term. This was a prospective cohort study. We recruited a group of nulliparous women at term with singleton pregnancy before the onset of labour in cephalic or breech presentation. A three-dimensional (3D) transperineal ultrasound (TPUS) volume was acquired for each woman at rest and saved for later analysis. SPA was measured on each volume using the previously validated linear reconstruction technique associated with volume contrast enhancement (Omniview-VCI; GE Healthcare, Zipf, Austria) by a single operator. Maternal characteristics and SPA values were compared between women with a fetus in cephalic vs. those in breech presentation. Overall, 124 women were recruited, among which 31 had a fetus in cephalic presentation and 93 in breech presentation. Among the latter group, 30 (96.7%) fetuses were in frank breech and 1 (3.3%) in footling presentation. Women in the breech presentation group had significantly narrower SPA values in comparison with a fetus in breech presentation had narrower SPA compared to women with a cephalic fetus (100°±9° vs 109°±15°, p < 0.001). Furthermore, women with a fetus in breech presentation had lower body mass index (BMI) compared to women with a fetus in cephalic presentation (25.9 ± 3.9 Kg/m2 vs 27.9 ± 5.0 Kg/m2, P=0.03). No other significant differences were found in the maternal characteristics between the 2 groups. Breech presentation is associated with narrower subpubic arch angle in nulliparous women at term.