Ultrasonic prediction of growth discordancy by intertwin difference in abdominal circumference.

Intertwin abdominal circumference (AC) and femur length (FL) differences were studied in 24 growth-discordant (greater than or equal to 15% birth weight difference) and in 32-growth concordant twin pairs delivered within 2 weeks of the last ultrasonic examination. Both groups were of similar gestational age but differed significantly in the mean twin birth weight and intertwin AC difference (P = 0.01 and P = 0.00009, respectively). A cutoff value (greater than or equal to 18 mm) for AC difference was found to discriminate significantly (P less than 0.0009) between concordant and discordant pairs with sensitivity, specificity, positive predictive value and negative predictive value of 66.7%, 78%, 69.5% and 75.7%, respectively. These data may suggest that an intertwin difference of 18 mm or more in AC effectively screens for the diagnosis of 15% or more birth weight difference in twin pregnancies.