Term twins with discordant birth weights: observations at birth and one year.

Sixteen pairs of term discordant twins (weight discrepancy of more than 20% when the lighter twin was compared to the heavier) were evaluated at birth. Weight, length, head circumference, anterior fontanel area, and combined ossification of the knee epiphyses were measured, and ponderal index (weight/length ratio) calculated. The most severely growth retarded infants had markedly decreased ossification and larger anterior fontanels. Eleven pairs had physical measurements at one year of age. With individual exceptions, the lighter twins at birth remained smaller in all dimensions. Despite these persistent differences between twin pairs, the values for length at one year of age were within normal limits for both the heavier and lighter twins. Infants without ossification at birth had a greater incremental linear growth by one year than those infants with ossification.