Normal and abnormal growth of multiples.

Growth curves of twins and triplets do not support a growth restriction patterns seen in singletons. At the same time that individual members of a twin or a triplet set may be smaller than singletons of the same gestational age, only a minority are indeed SGA by singleton standards. When comparing the entire 'fetal mass' of a multiple pregnancy to that of singletons, multiple gestations are in fact growth promoted, and their individual smaller size are better described as growth adaptation. Data from large twin and triplet series suggest that significant birth weight discordance result from the inability of the uterine milieu to equally nurture twins. In order to promote maturity - gestational age - mild compensation in the form of size discordance begins after mid-gestation. When the uterine environment competently nurtures multiples, total birth weight increases and discordance decreases. Failed adaptation, however, may result in significant growth discordance and restriction.