title: Measurement of subpubic arch angle by three-dimensional transperineal ultrasound and impact on vaginal delivery.
abstract: OBJECTIVE
  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 Cesarean section in the second stage of labor, and normal vs assisted vaginal delivery. The association between SPAA and the duration of second stage of labor was also analyzed.
  
  
  RESULTS
  Of the 625 women recruited initially, 14 ultrasound data files could not be retrieved, providing a total of 611 ultrasound images for measurement of SPAA. Complete obstetric and ultrasound data were obtained from 593 patients. Mean SPAA was 109.3° (range, 65.6-131.6°). There was no association between SPAA and the odds of a vaginal delivery (odds ratio, 1.01 (95% CI, 0.97-1.06)). However, there was evidence of an association between SPAA and duration of second stage of labor within the subgroup of women with a normal vaginal delivery (cause-specific hazard ratio, 1.02 (95% CI, 1.01-1.03); P = 0.003).
  
  
  CONCLUSIONS
  SPAA is not useful for predicting vaginal delivery; however, there is an association between this parameter and the duration of the second stage of labor.
authors: Department of Obstetrics and Gynecology, Johannes Gutenberg University, Mainz, Germany.
authors: S B
authors: SB
authors: Albrich
authors: Department of Obstetrics and Gynecology, Sydney Medical School Nepean, University of Sydney, Nepean Hospital, Penrith, NSW, Australia.
authors: K
authors: K
authors: Shek
authors: Institute of Medical Biostatistics, Epidemiology and Informatics (IMBEI), Johannes Gutenberg University, Mainz, Germany.
authors: U
authors: U
authors: Krahn
authors: Department of Obstetrics and Gynecology, Sydney Medical School Nepean, University of Sydney, Nepean Hospital, Penrith, NSW, Australia.
authors: H P
authors: HP
authors: Dietz
mesh_terms: D000293:Adolescent; D000328:Adult; D002585:Cesarean Section / Q000379:methods; D036861:Delivery, Obstetric / Q000379:methods*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D007231:Infant, Newborn; D007748:Labor Stage, Second / Q000502:physiology; D008297:Male; D015588:Observer Variation; D010298:Parity; D010502:Perineum; D011237:Predictive Value of Tests; D011247:Pregnancy; D011446:Prospective Studies; D011630:Pubic Bone / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D016216:Ultrasonography, Prenatal / Q000379:methods*
keywords: 3D ultrasound; mode of delivery; obstetrics; subpubic arch angle; vaginal delivery