Drought Exposure Linked to Higher Preterm Birth Risk

DROUGHT exposure during pregnancy may increase the likelihood of preterm birth, according to new research.

The nationwide Brazilian cohort study highlights how climate-related events may affect maternal and infant health, with more severe events associated with greater risk, particularly in populations experiencing greater socioeconomic and environmental vulnerability.

Tracking Drought Across Nearly 30 Million Births

Researchers analysed Brazilian birth, socioeconomic, and environmental data collected between 2001 and 2020. Almost 30 million live births were included in the primary analyses, of which approximately 8% were preterm.

Drought exposure was measured using the Standardized Precipitation Evapotranspiration Index (SPEI), which incorporates precipitation and evapotranspiration – the combined process of water evaporating from the ground and transpiring from plants into the atmosphere – to identify unusually dry conditions.

Researchers assessed drought accumulated over three, six, and nine month periods before birth, allowing them to examine both shorter and more prolonged exposures.

The outcomes investigated were preterm birth, defined as birth before 37 completed weeks; term low birth weight, defined as a birth weight below 2,500 g at 37 weeks or later; and small for gestational age (SGA).

Severe Drought Associated With Greater Prematurity Risk

Researchers found that drought was associated with approximately 2% higher odds of preterm birth across the three exposure periods. In absolute terms, this represented around 1.4 – 1.7 additional preterm births per 1,000 births in periods of aridity.

A dose-response pattern was particularly apparent for six month drought exposure. Compared with normal conditions, moderate drought was associated with 1% higher odds of preterm birth, increasing to 3% during severe drought and 5% during extreme drought.

However, associations varied considerably between populations. In municipalities with very low Human Development Index scores, six and nine month drought exposures were associated with 8% and 10% higher odds of preterm birth, respectively. Higher odds were also observed in the Amazon, Cerrado, and Pampa biomes.

Prolonged Drought Linked to Fetal Growth

The study found that drought was also associated with slightly higher odds of SGA. Following six and nine month exposures, there was approximately 0.8 – 1.5 additional cases of SGA per 1,000 births. Associations were particularly pronounced in the Amazon and Caatinga biomes.

However, researchers found no consistent association between drought and term low birth weight.

Drought and extreme heat also appeared to interact, with increasing numbers of extreme-heat events associated with progressively greater odds of preterm birth during drought conditions.

During six-month drought exposure, the odds ratio for preterm birth was 1.021  rising to 1.028 with 10 extreme-heat events and again to 1.031 with 20 events. The interaction between drought and extreme heat was statistically significant across all measured month exposure periods.

Climate Vulnerability and Maternal Health

Potential pathways linking drought to adverse pregnancy outcomes include food insecurity and maternal undernutrition, reduced water availability, dehydration, infectious disease, and heat stress, which may affect maternal health, placental function, and fetal development.

However, the observational study cannot establish causality. Drought exposure was measured at municipality level rather than individually, and the researchers noted potential limitations associated with administrative health records and socioeconomic measurements.

Nevertheless, as global temperatures continue to rise, the authors conclude that the findings support greater consideration of maternal and child health within climate adaptation strategies, particularly in socially and environmentally vulnerable communities.

Reference

Rocha AS, et al. Association between drought and adverse birth outcomes: a nationwide cohort study with 29.8 million live births in Brazil. The Lancet Regional Health – Americas. 2026.

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