Impact of Heat on Birth Outcomes and Child Nutrition: Study Protocol using the CIDACS Birth Cohort [version 1; peer review: 2 approved with reservations]

Background: Pregnant individuals and children are particularly vulnerable to the adverse health consequences of exposure to heat. Leveraging the robust ecosystem of Brazilian linked administrative data, we aim to advance our understanding of how high temperatures and heatwaves influence birth outcomes and child nutrition.

Objectives: Investigate the association between high ambient temperatures/ heatwaves and 1) birth outcomes (low birth weight (LBW), small for gestational age (SGA), large for gestational age (LGA), and preterm birth), 2) child nutrition (growth), and 3) breastfeeding practices and complementary feeding in children.

Methods: We will triangulate results from complementary analytical approaches, including time-stratified case-crossover designs and time-to-event techniques. We will explore the influence of high temperatures and heatwaves at different periods (or lags) preceding the event and apply distributed lag non-linear models to account for delayed and non-linear effects. We will conduct subgroup analyses to identify the population groups most at risk.

Results and Conclusions: Our study will generate new insights into the relationship between heat, birth outcomes, and child nutrition in Brazil. By providing evidence from a middle-income country with diverse ecosystems and climate zones in a context of social inequalities, this research will contribute to advancing the current knowledge base. Additionally, by identifying critical windows of vulnerability and at-risk groups, our findings can potentially inform targeted and equitable climate adaptation policies.