RESUMEN
Introduction It has been established that underweight women with low gestational weight gain (GWG) are at a higher risk of having Small for Gestational Age (SGA) newborns. However, the association remains poorly studied in Middle Eastern societies exhibiting different ethnic groups, genetic predisposing factors along with differences in nutritional food intake during pregnancy. The aim of this study is to assess the risk of having a SGA newborn among underweight and normal weight BMI women while studying the role of GWG in this association. Methods This is a retrospective cross-sectional study of 62,351 singleton pregnancies from the National Collaborative Perinatal Neonatal Network between 2001 and 2009 from 27 hospitals across Lebanon. Women who had underweight and normal pre-pregnancy BMI were included. Results A total of 8.6% newborns were SGA and 6.6% of women were underweight. Among women with normal and underweight pre-pregnancy BMI, 8.6 and 12.4% had SGA births respectively. Overall, the adjusted OR of having SGA newborns was significantly higher among underweight women (OR = 1.448; 95%CI = 1.287-1.630) compared to normal pre-pregnancy BMI. Below normal weight gain significantly increased the odds of SGA for both normal and underweight pre-pregnancy BMI women, with adjusted ORs of 1.535 (95% CI = 1.418-1.661) and 1.970 (95%CI = 1.515-2.560) respectively. Discussion Higher risks of SGA newborns in underweight and normal BMI women with low GWG were observed. In addition, normal weight gain couldn't protect underweight women of having risk for SGA newborns. Hence, all pregnant women should be encouraged to maintain healthy BMI before pregnancy and attain adequate GWG.