title: Antenatal pelvic floor biometry is related to levator ani muscle injury.
abstract: OBJECTIVE
  To evaluate the relationship between antenatal pelvic floor biometry and levator ani muscle (LAM) injury in Chinese women.
  
  
  METHODS
  Three-dimensional transperineal ultrasound was performed in nulliparous Chinese women with a singleton pregnancy at 9-12 weeks, 26-28 weeks and 36-38 weeks of gestation and again at 12 months after delivery. Hiatal anteroposterior (AP) diameter, transverse diameter and area were measured on the antenatal ultrasound volumes obtained at rest, on Valsalva maneuver and during pelvic floor muscle contraction (PFMC). LAM injury was evaluated using ultrasound volumes obtained during PFMC at 12 months after delivery.
  
  
  RESULTS
  In total, 328 women completed the study. At 12 months after delivery, 38 (14.8% of those who delivered vaginally) women had LAM injury; 28 were unilateral (14 right- and 14 left-sided) and 10 were bilateral. In all three trimesters there was smaller hiatal AP diameter and hiatal area in women with LAM injury when compared with women without injury. On multivariable analysis of the three factors, hiatal AP diameter at rest, hiatal area at rest and operative vaginal delivery, only hiatal AP diameter at rest in all three trimesters was an independent factor of LAM injury. A larger hiatal AP diameter at rest in the first, second and third trimesters reduced the likelihood of LAM injury with odds ratios of 0.21, 0.15 and 0.21, respectively.
  
  
  CONCLUSIONS
  A smaller antenatal hiatal AP diameter at rest is a risk factor for LAM injury. The hiatal AP diameter is relatively simple to measure and the error in measurement is relatively small. A prospective study to confirm this relationship and to explore whether this measurement, performed in the midsagittal plane, is repeatable should be performed. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
authors.affiliation: Department of Obstetrics and Gynaecology, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, China. symphorosa@cuhk.edu.hk.
authors.forename: S S C
authors.initials: SS
authors.lastname: Chan
authors.affiliation: Department of Obstetrics and Gynaecology, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, China.
authors.forename: R Y K
authors.initials: RY
authors.lastname: Cheung
authors.affiliation: Department of Obstetrics and Gynaecology, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, China.
authors.forename: K W
authors.initials: KW
authors.lastname: Yiu
authors.affiliation: Department of Obstetrics and Gynaecology, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, China.
authors.forename: L L
authors.initials: LL
authors.lastname: Lee
authors.affiliation: Department of Obstetrics and Gynaecology, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, China.
authors.forename: T K H
authors.initials: TK
authors.lastname: Chung
mesh_terms: D000328:Adult; D002681:China; D005260:Female; D005865:Gestational Age; D006801:Humans; D021621:Imaging, Three-Dimensional; D009119:Muscle Contraction; D017773:Pelvic Floor / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000293:injuries*; D011247:Pregnancy; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal / Q000379:methods*
keywords: hiatal AP diameter; hiatal area; hiatal dimension; levator ani muscle injury; pelvic floor biometry