Methods: We included participants who were enrolled during pregnancy with a singleton fetus, lived in the conterminous U.S. with geocoded residential address history data for at least 80% of their pregnancy, and had birth outcomes data. Monthly prenatal residential locations were linked to county-level Standardized Precipitation Evapotranspiration Index (SPEI). Drought intensity and an indicator for drought (SPEI<-1.0) were used to calculate a time-weighted measure of drought exposure during pregnancy, which was dichotomized at the sample median for analyses. Mixed models with random intercepts for cohort site were used to estimate associations between drought and birth outcomes (gestational age, preterm birth, birth weight, low birth weight, birthweight-for-gestational age z-score) adjusting for birthing parent’s age at delivery, pre-pregnancy body mass index, education, parity, prenatal tobacco use, infant sex and birth year, rurality, and neighborhood-level socioeconomic vulnerability index.
Results: The study included 26,534 pregnant people across the U.S. between 2000-2023, over. half of whom birthing individuals were exposed to drought for at least one month of their pregnancy. The median time-weighted average exposure was 0.11 (range, 0-0.875). Those experiencing drought during a higher-than-average proportion of their pregnancy had 2.55 times the odds of preterm delivery (aOR=2.55; 95% CI 2.26, 2.87) and half a week shorter gestation on average (β=-0.50; 95% CI -0.59, -0.41). Prenatal exposure to higher-than-average drought was associated with lower mean birthweight but not birthweight-for-gestational age z-score.
Conclusion: Our findings suggest that relatively low prenatal exposure to drought is associated with adverse birth outcomes. Future research should investigate effect measure modifiers, mechanisms, and opportunities for intervention to reduce drought-related adverse birth outcomes.
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