Effect of prenatal food supplementation on birth weight: an observational study from Bangladesh. 
National nutrition programs in Bangladesh have included prenatal food supplementation to reduce maternal and child malnutrition.  The knowledge base is weak regarding the effect of prenatal food supplementation on the birth weight (BW) of infants in populations in whom low BW is prevalent and regarding any variation in effect based on maternal nutritional status.  We examined whether observational data support an effect of daily prenatal food supplementation on BW by considering the duration of supplementation and whether the effect is modified by maternal postpartum weight (a proxy of prepregnancy weight) groups.  A cohort of undernourished pregnant women (n = 777) who received prenatal food supplementation (608 kcal/d) was followed.  The association between the uptake of food supplements and BW was analyzed after adjustment for potential confounders (n = 619 with complete information).  Differential effects in lower and higher maternal postpartum weight groups were examined.  The average BW was 2521 g. On average, the women received daily supplements for 4 mo, which resulted in an increase in BW of 118 g (1.0 g/d).  The strongest effect was found for births occurring in January and February.  There was a linear dose-response relation between duration of supplementation and BW for women with higher postpartum weights (> or = 42 kg, above the median).  In women with lower weights (< 42 kg, below median), a shorter duration of supplementation (< 4 mo) had no such dose-response relation with BW, but there was a linear dose-response relation for longer durations of supplementation.  The association between duration of prenatal food supplementation and BW varies with maternal postpartum weight.  A large effect was observed after the season with food insecurity (mid-August to mid-November).