Doppler velocimetry in concordant and discordant twin gestations

Doppler blood flow studies in 63 pairs of concordant and 17 pairs of discordant twins were compared with those of 277 appropriate for gestational age singleton fetuses. Discordancy was defined as a more than 20% intra-pair actual birth weight difference. The data were divided into five groups: singletons and large and small concordant and discordant twins. Statistical comparisons of the regression lines for the large concordant and discordant twins and the singletons showed no significant differences among the three lines, either in slopes (P = .1) or intercepts (P = .08). Comparisons of the regression lines for small concordant and discordant twins and the singletons indicated a significant interaction among the three lines (P = .01). Additional analysis leads us to conclude that the systolic-diastolic ratio (S/D) decreases with advancing gestational age for all groups except small discordant twins. The S/D of small discordant twins differed significantly from that of singletons and tended to differ from that of small concordant twins.