The timing of maternal weight gain during pregnancy and fetal growth.

The morbidity, mortality, and growth patterns of intrauterine growth retarded (IUGR) infants vary according to body proportionality, or the ponderal index. Much less in known, however, about the factors that give rise to the various forms of IUGR. This study tests that hypothesis that the rate of maternal weight gain during early/mid and late pregnancy are differentially related to body size and proportions at birth in a nutritionally stressed population in rural Malawi. The data consist of prospectively collected measurements of maternal weight and infant size at birth on 272 mother-infant pairs. The results reveal that early/mid and late weight gain are both related to birth weight and length, but not to the ponderal index. Late weight gain is particularly predictive of infant size among thin women (BMI </= 18.5) and is several times stronger than early/mid weight gain. These findings do not support the timing hypothesis as previously stated in the literature, but do add to the suggestions arising from a disparate literature that growth acceleration in length may precede acceleration in weight-for-length during a period of nutritional replection in phases of the life cycle characterized by rapid growth. Am. J. Hum. Biol. 11:627-637, 1999. Copyright 1999 Wiley-Liss, Inc.