Birthweight doubling time: a fresh look.

Infant birthweight doubling time is widely quoted as being achieved between 5 and 6 months. The purpose of this study was to determine the time of birthweight doubling and to identify important related variables. A total of 357 normal infants with birthweights between 2,500 and 4,100 gm were studied. Mean age of birthweight doubling for the entire group was 119 days (3.8 months). Bottle-fed infants doubled their birthweights earlier than breast-fed infants: 113 days vs. 124 days (P less than .05). Boys doubled their birthweights earlier than girls: 111 days vs. 129 days (P less than .0001). Solids were introduced earlier in bottle-fed infants (mean , 1.9 months) than in breast-fed infants (mean, 3.9 months). Harvard percentiles for mean group weight and length at the time of birthweight doubling were: for bottle-fed infants, 75th and 55th percentiles respectively: for breast-fed infants, 55th and 60th percentiles respectively; for boys, 75th percentile for both weight and length; for girls, 50th percentile for both weight and length. Thus, bottle-fed infants appear to have weight gains in excess of length gain and may be developing early obesity. In light of the poor prognosis in treating obesity, closer supervision of early infant feeding practices is indicated.