title: Changes in Cesarean section scar dimensions during pregnancy: a prospective longitudinal study.
abstract: OBJECTIVE
  To describe changes in Cesarean section (CS) scars longitudinally throughout pregnancy, and to relate initial scar measurements, demographic variables and obstetric variables to subsequent changes in scar features and to final pregnancy outcome.
  
  
  METHODS
  In this prospective observational study we used transvaginal sonography (TVS) to examine the CS scar of 320 consecutive pregnant women at 11-13, 19-21 and 32-34 weeks' gestation. For scars visible on TVS, the hypoechoic part was measured in three dimensions and the residual myometrial thickness (RMT) was also measured. Analyses were carried out using one-way repeated measures ANOVA and mixed modeling. The incidence of subsequent scar rupture was recorded.
  
  
  RESULTS
  The CS scar was visible in 284/320 cases (89%). Concerning length and depth of the hypoechoic part of the scar and RMT, the larger the initial scar measurement, the larger the decrease observed during pregnancy. For the hypoechoic part of the scar, the width increased on average by 1.8 mm per trimester, while the depth and length decreased by 1.8 and 1.9 mm, respectively (false discovery rate P < 0.0001). Mean RMT in the first trimester was 5.2 mm and on average decreased by 1.1 mm per trimester. Two cases (0.62%) of uterine scar rupture were confirmed following a trial of vaginal delivery; these had a mean RMT of 0.5 mm at second scan and an average decrease of 2.6 mm over the course of pregnancy.
  
  
  CONCLUSIONS
  This study establishes reference data and confirms that the dimensions of CS scars change throughout pregnancy. Scar rupture was associated with a smaller RMT and greater decrease in RMT during pregnancy. There is the potential to test absolute values and observed changes in CS scar measurements as predictors of uterine scar rupture and outcome in trials of vaginal birth after Cesarean section.
authors.affiliation: Obstetrics and Gynecology Unit, Queen Charlottes and Chelsea Hospital, Imperial College London, London, UK.
authors.forename: O
authors.initials: O
authors.lastname: Naji
authors.forename: A
authors.initials: A
authors.lastname: Daemen
authors.forename: A
authors.initials: A
authors.lastname: Smith
authors.forename: Y
authors.initials: Y
authors.lastname: Abdallah
authors.forename: S
authors.initials: S
authors.lastname: Saso
authors.forename: C
authors.initials: C
authors.lastname: Stalder
authors.forename: A
authors.initials: A
authors.lastname: Sayasneh
authors.forename: A
authors.initials: A
authors.lastname: McIndoe
authors.forename: S
authors.initials: S
authors.lastname: Ghaem-Maghami
authors.forename: D
authors.initials: D
authors.lastname: Timmerman
authors.forename: T
authors.initials: T
authors.lastname: Bourne
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D002585:Cesarean Section / Q000009:adverse effects*; D002921:Cicatrix / Q000000981:diagnostic imaging / Q000473:pathology*; D005260:Female; D006801:Humans; D011247:Pregnancy; D011248:Pregnancy Complications / Q000000981:diagnostic imaging / Q000473:pathology*; D011256:Pregnancy Outcome; D011264:Pregnancy Trimesters; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal; D014597:Uterine Rupture / Q000209:etiology / Q000473:pathology