EP19.02: Levator ani muscle coactivation is associated with breech presentation in nulliparous women at term

The aim of the present study was to evaluate the correlation between levator ani muscle coactivation and breech presentation in nulliparous women at term. We also aimed to compare the anteroposterior diameter (APD) of the levator ani muscle (LAM) hiatus at rest, contraction and under maternal pushing between nulliparous women with fetuses in cephalic vs. breech presentation 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. Each woman underwent 2D transperineal ultrasound at rest, at maximum pelvic floor muscle contraction and with maternal pushing (Valsalva). LAM coactivation is defined when APD at maximum maternal pushing is smaller than APD at rest, reflecting a contraction rather than relaxation of LAM with pushing. APD at rest, at pushing and the prevalence of LAM coactivation was compared between the cephalic vs. breech presentation groups. Overall, 124 women were recruited, among which 31 had a fetus in cephalic presentation and 93 in breech presentation. Women in the breech presentation group had smaller APD under pushing (52 ± 11mm vs 57 ± 9 mm, P=0.03), a higher prevalence of LAM coactivation (32% vs 14%, P=0.02), and smaller change of APD from rest to maximum pushing (2 ± 5 vs 5 ± 6 mm, P < 0.001) in comparison with the cephalic presentation group. APD at rest and other maternal characteristics were not significantly different between the 2 groups. Proper pelvic floor relaxation seems to favour fetal cephalic presentation. Levator ani muscle coactivation and smaller increase of the anteroposterior diameter of the levator ani muscle hiatus at maternal pushing in nulliparous women at term are associated with an increased risk of breech presentation.