title: Fetal transcerebellar diameter measurement for prediction of gestational age in twins.
abstract: OBJECTIVE
  This study was undertaken to determine the accuracy of our previously published and prospectively validated institution-specific singleton transcerebellar diameter (TCD) nomogram in the prediction of gestational age (GA) in twin pregnancies. We further evaluated whether the prediction of GA in twin gestations using the singleton TCD nomogram differs between monochorionic and dichorionic twins.
  
  
  METHODS
  In our previously published studies, we retrospectively constructed a cross-sectional nomogram using TCD measurements in 24,026 well-dated, singleton fetuses, and prospectively validated the nomogram using 2,597 singleton fetuses. The current study comprised of 1,278 well-dated twins (19.6% monochorionic) seen in our ultrasound unit between August 1994 and May 2003, and the singleton TCD nomogram was validated in these twin gestations. The actual GA was subtracted from the GA predicted by the TCD nomogram and the concordance between actual and predicted GAs was assessed on the basis of the Pearson's correlation coefficient (r). This was performed separately for monochorionic and dichorionic twins.
  
  
  RESULTS
  Concordance between the actual and predicted twin TCD measurements based on our previously published singleton TCD nomogram was high (Pearson's correlation, r = 0.95, P < .0001). Between 16 and 23 weeks' gestation, the predicted mean GA was within 6 days of actual GA. Between 24 and 30 weeks, the predicted mean GA was within 3 days, and at 32 weeks or more, the predicted mean GA was within 5 days of the actual GA. Prediction of GA based on the singleton TCD nomogram was equally accurate in both monochorionic and dichorionic twin gestations (P = .686).
  
  
  CONCLUSIONS
  This study demonstrates that our previously validated singleton TCD nomogram is reliable and accurate in twins irrespective of placental chorionicity.
authors.affiliation: Division of Maternal-Fetal Medicine, Department of Obstetrics, Gynecology and Reproductive Sciences, UMDNJ-Robert Wood Johnson Medical School/Robert Wood Johnson University Hospital, New Brunswick, NJ, USA.
authors.forename: Martin R
authors.initials: MR
authors.lastname: Chavez
authors.forename: Cande V
authors.initials: CV
authors.lastname: Ananth
authors.forename: Lillian M
authors.initials: LM
authors.lastname: Kaminsky
authors.forename: John C
authors.initials: JC
authors.lastname: Smulian
authors.forename: Lami
authors.initials: L
authors.lastname: Yeo
authors.forename: Anthony M
authors.initials: AM
authors.lastname: Vintzileos
mesh_terms: D000328:Adult; D002531:Cerebellum / Q000000981:diagnostic imaging*; D005260:Female; D005865:Gestational Age; D006801:Humans; D049451:Nomograms; D011237:Predictive Value of Tests; D011247:Pregnancy; D011272:Pregnancy, Multiple; D015203:Reproducibility of Results; D014427:Twins; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D016216:Ultrasonography, Prenatal