[Relationship between maternal anthropometry and weight gain with birth weight, and risks of low birth weight, small for gestational age and prematurity at an urban population of Buenos Aires, Argentina].

To asses the relationship between body mass index and net weight gain during pregnancy with birth weight and the risks of low birth weight, small for date and prematurity 9613 records from Sardá's Perinatal Database between 1994-1995 were reviewed. Exclusion criteria were fetal death, twin pregnancy, congenital malformations, lack of prenatal visits and lack of preconceptional weight and height. 9.6% of mothers and 15% of adolescents presented with low preconceptional BMI (median: 24.8 +/- 4.3 kg/m2); in contrast, 28% were overweight and obese. Net weight gain (median 9.25 +/- 4.9 kg) accounted for 16% of previous weight and was higher with lower BMI (p = 0.001). Birth weight (median 3375 +/- 467 g) decreased with lower BMI (p = 0.001) and the risks of low birth weight (p < 0.05), small for date (p < 0.05), and prematurity (p = 0.05) was independently associated with BMI, and increased (p < 0.001) when lower the net weight gain was. The best predictors for low birth weight, small for date and prematurity risks were low preconceptional weight (40-51 kg) (adjusted OR 1.72; [95%CI 1.48-1.95], 2.12 [1.82-2.41] and 1.46 [1.12-1.79] respectively). Net weight gain and several predictive variables did not explain more than 10.8% of the variability of birth weight. Preconceptional weight should have important implications for the design of future nutritional strategies at a poblational level, especially for adolescents.