Objective: To investigate the effect of maternal exposure to different seasons during the second and third trimester of pregnancy on infant birth weight in rural Bangladesh.
Method: Information on 3,831 singleton live births was obtained from the electronic databases of Matlab Health and Demographic Surveillance System and Matlab hospital of the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b). We collected information on all term births from July 2011 to June 2015 and excluded congenital anomalies and observations with missing data. Each year was divided into three distinct seasons: the post-aman harvest period (January-April), the height of the monsoon (May-August) and the post-aus harvest period (September-December). Seasonal exposure was measured in weeks and multivariable linear regression models were fitted to determine the independent effect of each week exposure of different season during the second and third trimesters of pregnancy on birth weight.  
Result: We observed peak birth weight in post-aman harvest season, especially among babies born in March (2930.5±462.1 gm) and the lowest birth weight in the month of July (2830.6±385.4 gm) during the monsoon season. Regression analysis showed that exposure to post-aman harvest season during the third trimester of pregnancy had significant positive effect on birth weight. In the adjusted model, each week exposure to post-aman harvest season during third trimester caused 6.3 gm (95% CI: 1.6, 10.9; p = 0.008) increase in birth weight. 
Conclusion: Infants born to women who have been exposed to the post-aman harvest season for the entire third trimester (14 weeks) are likely to be heavier by 88.2 g at birth. Further investigations into the complex interplay between seasonal energy stress, maternal and fetal nutrition and measures to alleviate it are warranted.