Risk and burden of adverse birth outcomes associated with flood exposure in China: A 4.4 million mother-infant cohort study.

The risks and attributable burden of adverse birth outcomes from flooding remain unclear. Here, we analyzed a nationwide cohort of over 4.4 million mother-infant pairs in China, matching a spatiotemporal flood database with multiple buffer zones centered on maternal delivery hospitals to assess the health risks of multi-window flood exposure before and during pregnancy. We found that flood exposure during the three months preconception and the first trimester significantly increased the risks of preterm birth (PTB), low birth weight (LBW), small for gestational age (SGA), and term low birth weight (TLBW). Based on exposure assessment within a 3000-meter buffer, we estimate that between 2013 and 2019, first-trimester flood exposure accounted for 925,717 attributable cases of PTB (95% Uncertainty Interval [UI]: 814,446-1,035,426), with an attributable fraction (AF) of 13.56%; 418,333 cases of LBW (95% UI: 359,916-475,711; AF, 13.47%); 263,977 cases of SGA (95% UI: 101,700-424,152; AF, 2.81%); and 591,283 cases of TLBW (95% UI: 364,246-810,774; AF, 9.23%). This study quantifies a major perinatal health burden from flooding and identifies critical windows for intervention before and during early pregnancy.