This study was undertaken to determine the effect of pregravid body weight and weight gain during pregnancy on birth weight of term newborns.The study population consisted of 1443 healthy women, who delivered of singleton, live infants at or beyond 38 weeks of gestation. Maternal pregravid weight was obtained by recall and categorized into quartiles: 65 (kg). Women were further divided according to their gestational weight gain into quartiles: 15.5 (kg). Birth weight was measured and recorded at delivery. Newborns were classified as hypotrophic (SGA; 90th percentile).The mean birth weight in the study population was 3499 +/- 447 g, 8.5% infants met the criteria for SGA, and 9.4%--for LGA. Studies showed that a progressive increase in maternal pregravid weight as well as gestational weight gain effect independently on increase birthweight, although the effect of weight gain during pregnancy was lessened as weight before gestation increased. For example, increasing gestational weight gain from 15.5 kg increased mean birthweight by 385 g (12.1%) for pregravid weight of 53 kg or less, compared with 142 g (4.0%) for weight of more than 65 kg. They were also associated with decreased frequency of hypotrophic infants and increased frequency of hypertrophic neonates.Both maternal prepregnancy weight and weight gain during gestation are important factors affecting fetal growth and birth weight. Increasing maternal weight before pregnancy diminishes the influence of weight gain on birthweight. As pregravid weight and prenatal weight gain increase, the incidence of LGA also increase, whereas the frequency of SGA decreases.