The association between timing in pregnancy of drought and excess rainfall, infant sex, and birthweight: Evidence from Nepal

Background: Past research on the impact of climatic events, such as drought, on birth outcomes has primarily been focused in Africa, with less research in South Asia, including Nepal. Existing evidence has generally found that drought impacts birthweight and infant sex, with differences by trimester. Additionally, less research has looked at the impact of excess rain on birth outcomes or focused on the impact of rainfall extremes in the preconception period. Using data from a large demographic surveillance system in Nepal, combined with a novel measure of drought/excess rainfall, we explore the impact of these on birthweight by time in pregnancy.

Methods: Using survey data from the 2016 to 2019 Chitwan Valley Study in rural Nepal combined with data from Climate Hazards InfraRed Precipitation with Station, we explored the association between excess rainfall and drought and birthweight, looking at exposure in the preconception period, and by trimester of pregnancy. We also explore the impact of excess rainfall and drought on infant sex and delivery with a skilled birth attendant. We used multilevel regressions and explored for effect modification by maternal age.

Results: Drought in the first trimester is associated with lower birthweight (β = -82.9 g; 95% confidence interval [CI] = 164.7, -1.2) and drought in the preconception period with a high likelihood of having a male (odds ratio [OR] = 1.41; 95% CI = 1.01, 2.01). Excess rainfall in the first trimester is associated with high birthweight (β = 111.6 g; 95% CI = 20.5, 202.7) and higher odds of having a male (OR = 1.48; 95% CI = 1.02, 2.16), and in the third trimester with higher odds of low birth weight (OR = 2.50; 95% CI = 1.40, 4.45).

Conclusions: Increasing rainfall extremes will likely impact birth outcomes and could have implications for sex ratios at birth.