Low birthweight and postnatal weight in full-term infants under six months old, Rio de Janeiro, RJ, Brazil.

This study investigated the association between low birthweight and postnatal weight in full-term infants, taking social, economic, maternal and babies characteristics into account. A cross-sectional study was conducted with infants under six months old at 27 primary healthcare units in the Rio de Janeiro municipality, Brazil, in 2007. Only singleton full-term babies were included. The association between full-term low birthweight and postnatal weight was tested using the multiple regression model adjusted for the gender and age of the baby, as well as potential confounding factors. A total of 875 babies were evaluated, of whom 4.5% were small for gestational age. Small-for-gestational-age babies weighted, on average, 977.4 grams less than those born with adequate weight for gestational age, after adjustment by gender and age, as well as marital status and parity. Girls were 426.74 grams lighter than boys; children from mothers with live-in partners were 146.2 grams heavier than those of single mothers, and the babies of primiparae weighed 204.67 grams less than the children of multiparae. Low birthweight is an unfavorable factor for postnatal weight of full-term infants. These children, particularly daughters of primipara single mothers, must be followed more frequently in relation to their postnatal growth.