Measurement of subpubic arch angle by three-dimensional transperineal ultrasound and impact on vaginal delivery

Objectives To assess whether antepartum measurement of the subpubic arch angle (SPAA) as a parameter of the bony pelvic outlet can predict vaginal delivery. Methods Between January 2007 and June 2011, 625 nulliparous women with a singleton pregnancy were recruited from the antenatal clinic to be interviewed and have a four-dimensional transperineal ultrasound examination. Ultrasound examinations were performed between 34 and 36 weeks of gestation. Volume ultrasound data were saved for offline analysis, blinded against all other data. The SPAA was measured in the axial plane and logistic regression analysis was used to examine the association between SPAA and outcomes of vaginal delivery vs …