title: Clinical implications of intra- and interobserver reproducibility of transvaginal sonographic measurement of gestational sac and crown-rump length at 6-9 weeks' gestation.
abstract: OBJECTIVE
  To assess intra- and interobserver agreement of routinely performed measurements-crown-rump length (CRL) and mean gestational sac diameter (MSD)-for assessing the likelihood of miscarriage in the first trimester of pregnancy using transvaginal sonography.
  
  
  METHODS
  A cross-sectional study of CRL and gestational sac measurements in first-trimester pregnancies was conducted in a fetal medicine referral center with a predominantly Caucasian population. Gestational age ranged from 6 to 9 weeks. All patients underwent a transvaginal ultrasound examination using a high-resolution ultrasound machine. Two measurements of CRL and measurements of three diameters of the gestational sac were obtained by two observers. Agreement within and between observers for CRL and between observers for MSD was analyzed using 95% prediction intervals, Bland-Altman plots with 95% limits of agreement and the intraclass correlation coefficient (ICC).
  
  
  RESULTS
  In total 54 patients were included in the study, with measurements obtained by both observers in 44 of these. Intra- and interobserver ICCs were high for CRL measurements, with values of 0.992 and 0.993 for intraobserver agreement and 0.993 for interobserver agreement. For the MSD, the interobserver ICC was 0.952. Limits of agreement were ± 8.91 and ± 11.37% for intraobserver agreement of CRL and ± 14.64% for interobserver agreement of CRL. For MSD, the interobserver limits of agreement were ± 18.78%. For an MSD measurement of 20 mm by the first observer, the prediction interval for the second observer was 16.8-24.5 mm. For a CRL measurement of 6 mm, the prediction interval for the second observer was 5.4-6.7 mm.
  
  
  CONCLUSIONS
  For dating purposes, there is reasonable reproducibility of CRL measurements using transvaginal ultrasonography at 6-9 weeks' gestation. When diagnosing miscarriage based on measurements of CRL care must be taken for values close to any decision boundary. The higher interobserver variability that we observed for MSD has implications for the diagnosis of miscarriage based on this measurement in the absence of a visible embryo or yolk sac.
authors.affiliation: Department of Obstetrics and Gynaecology, University Hospitals, Katholieke Universiteit Leuven, Leuven, Belgium. annepexsters@hotmail.com
authors.forename: A
authors.initials: A
authors.lastname: Pexsters
authors.forename: J
authors.initials: J
authors.lastname: Luts
authors.forename: D
authors.initials: D
authors.lastname: Van Schoubroeck
authors.forename: C
authors.initials: C
authors.lastname: Bottomley
authors.forename: B
authors.initials: B
authors.lastname: Van Calster
authors.forename: S
authors.initials: S
authors.lastname: Van Huffel
authors.forename: Y
authors.initials: Y
authors.lastname: Abdallah
authors.forename: T
authors.initials: T
authors.lastname: D'Hooghe
authors.forename: C
authors.initials: C
authors.lastname: Lees
authors.forename: D
authors.initials: D
authors.lastname: Timmerman
authors.forename: T
authors.initials: T
authors.lastname: Bourne
mesh_terms: D000022:Abortion, Spontaneous / Q000000981:diagnostic imaging*; D000328:Adult; D003430:Cross-Sectional Studies; D018568:Crown-Rump Length; D005260:Female; D058746:Gestational Sac / Q000000981:diagnostic imaging*; D006801:Humans; D015588:Observer Variation; D011237:Predictive Value of Tests; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal