Fetal transcerebellar diameter measurement for prediction of gestational age in twins

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. Study design 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 Pearsonʹs 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 (Pearsonʹs correlation, r = 0.95, P< .0001). Between 16 and 23 weeksʹ 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). Conclusion This study demonstrates that our previously validated singleton TCD nomogram is reliable and accurate in twins irrespective of placental chorionicity.