title: Ultrasound Assessment of Lower Uterine Segment Thickness During Pregnancy, Labour, and the Postpartum Period.
abstract: OBJECTIVE
  To evaluate the normal ranges of lower uterine segment (LUS) thickness throughout pregnancy in women without a previous cesarean and to evaluate the relationship between ultrasound and intraoperative LUS thickness.
  
  
  METHODS
  We assessed LUS thickness using transabdominal and transperineal longitudinal scan at each week of gestation, during labour, and in the postpartum period in 1000 pregnant women without previous CS. Secondly, we assessed LUS thickness immediately before CS (using ultrasound) and intraoperatively (using ophthalmic calipers) immediately before delivery of the fetus in 35 women with a previous CS and 29 women without previous CS undergoing elective CS before labour.
  
  
  RESULTS
  We performed 20 307 LUS thickness measurements in between 119 and 944 women at each week of gestation, in 944 women during labour, and in 936 women after delivery. We observed a strong relationship between transabdominal and transperineal ultrasound (P < 0.001) and an inverse correlation between LUS thickness and gestational age (P < 0.001), with a mean thickness of 5.1 ± 1.4 mm at 20 weeks, 3.6 ± 1.3 mm at 30 weeks, and 2.3 ± 0.6 mm at 40 weeks of gestation. In women undergoing elective CS, we observed a strong relationship between antepartum and intraoperative LUS thickness (P < 0.001), with mean thicknesses of 2.2 ± 0.7 mm in 28 women without thinning of LUS; 0.8 ± 0.1 mm in four women with grade II uterine scar dehiscence; and 0.4 ± 0.1 mm in three women with grade III dehiscence. A LUS myometrial thickness less than 1.2 mm could have predicted all grade II and grade III uterine scar dehiscences without false-positive cases.
  
  
  CONCLUSIONS
  LUS thickness decreases with gestational age and correlates strongly with the intraoperative LUS thickness in women with a previous CS.
authors.affiliation: M&K Health Institute, Hyogo, Japan.
authors.forename: Misao
authors.initials: M
authors.lastname: Fukuda
authors.affiliation: M&K Health Institute, Hyogo, Japan.
authors.forename: Kiyomi
authors.initials: K
authors.lastname: Fukuda
authors.affiliation: Shimizu Women's Clinic, Hyogo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Shimizu
authors.affiliation: Department of Obstetrics and Gynaecology, Centre de Recherche du CHU de Québec, Faculty of Medicine, Université Laval, Quebec City QC.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Bujold
mesh_terms: D000328:Adult; D005260:Female; D005865:Gestational Age; D006801:Humans; D007743:Labor, Obstetric / Q000502:physiology*; D049590:Postpartum Period / Q000502:physiology*; D011247:Pregnancy / Q000502:physiology* / Q000706:statistics & numerical data*; D011446:Prospective Studies; D014463:Ultrasonography; D014599:Uterus / Q000000981:diagnostic imaging*; D055815:Young Adult
keywords: Caesarean; LUS; Lower uterine segment; labour; postpartum; pregnancy; ultrasound; uterine scar