Association of Pre-Pregnancy Body Mass Index and Gestational Weight Gain with Preterm Births and Fetal Size: an Observational Study from Lebanon

Background: Pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) are reported to impact the preterm birth (PTB) rate and newborn size. Most studies have been conducted in developed countries, although PTB and adverse pregnancy outcomes are more frequent in the developing world. The aim of this study is to elucidate the association of pre-pregnancy BMI and GWG on the occurrence of PTB and sub-optimal fetal size in Lebanon. Methods: This is a retrospective cohort study using a hospital-based register covering 35% of births in Lebanon between 2001 and 2012. Data were collected on 170 428 pregnancies from 32 hospitals using medical records and interviews. Results: After adjusting for confounders, underweight women had increased odds of having very preterm [odds ratio (OR) 1.58, 95% confidence interval (CI) 1.16, 2.14], preterm (OR 1.42, 95% CI 1.28, 1.58), and small for gestational age (SGA) (OR 1.50, 95% CI 1.37, 1.63) neonates. When BMI was analysed with GWG, only SGA remained significant in underweight women with low GWG. For all BMI groups, low GWG was protective against large for gestational age (LGA) and high GWG increased the odds of LGA. GWG, both low (OR 1.25, 95% CI 1.15, 1.35) and high (OR 1.43, 95% CI 1.32, 1.55) increased the risk of PTB in normal weight women. The same result was obtained for overweight women. Conclusions: High GWG increased the risk of LGA for all groups and PTB in normal weight and overweight women, whereas low GWG increased the risk of SGA and PTB. Given that there are not many studies from middle income/developing countries on patterns of weight gain during pregnancy, findings from this study may help with pre-conception counselling with emphasis on the importance of an optimal pre-pregnancy BMI and appropriate weight gain during pregnancy.