Objective: To determine differences between growth patterns of monochorionic and dichorionic twins, and of concordant and discordant twins of both chorionicities. Methods: We studied 70 cases of concordant twins (24 monochorionic, 46 dichorionic) and 45 cases of discordant twins (25 monochorionic, 20 dichorionic). In each case, growth was measured longitudinally by ultrasound biometry and the growth pattern was depicted. Results: There were no differences in incremental growth between concordant monochorionic and dichorionic twins. The growth curve of concordant twins of both chorionicities was almost the same as that of a singleton until 34 weeks' gestation. However, in the discordant twins, the growth of the larger twin matched the growth curve of a singleton or concordant twin, but the growth of the smaller twin gradually decreased to the range of growth restriction. The growth curves for monochorionic discordant twins appeared to be representative of two groups, one of which had onset of discordancy before 24 weeks. Conclusion: It is clinically important to determine chorionicity early in twin pregnancies, to calculate the percentage of discordancy between the fetuses, and to examine longitudinal fetal growth curves in each chorionicity. Copyright (C) 2000 The American College of Obstetricians and Gynecologists.
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