A comparison of the early growth of twins and singletons

Background: It is well known that the birth weight of twins is less than that of singletons, but there is less information about how birth lengths compare and how twins grow in the postnatal and early childhood period. The implications of the shorter duration of gestation of twins in comparing their postnatal progress with that of singletons are seldom taken into consideration. Aims: The study aimed to compare the growth of healthy twins and singletons over the first 4 years of life. Subjects and methods: Birth length data on English twins born between 1990 and 1997 were used to produce reference values for gestational ages from 33 to 40 weeks. Follow-up data of weights and lengths up to the equivalent of 40 weeks' gestation are reported on some of these infants who were born pre-term. On the basis of questionnaires, the growth of twins in terms of weight, length/height and head circumference has been followed up to 4 years of age. Results: Mean birth length of twins showed a fall-off when compared with singletons at comparable gestational ages, which was more marked in boys than girls and evident earlier. Extrauterine growth of twins born pre-term was comparable to that of adequately nourished twins remaining in utero until term. Much of the smallness of twins at birth was because of their shorter gestation. Subsequently singletons gained weight faster. Lengths/heights showed no deficit compared with singletons. Head circumferences of twins were, however, smaller than singletons throughout. Conclusions: The early growth of normal twins differs markedly from that of singletons. It is important to recognize that singleton reference values do not correctly reflect the growth of twins.