High ambient temperature during pregnancy and offspring cerebral palsy: A population-based case-control study in California

BACKGROUND: Cerebral palsy (CP) is the most common neuromotor disorder in childhood and environmental factors may play important etiological roles. We aimed to investigate whether prenatal exposure to high ambient temperature was associated with CP risk in the offspring. METHODS: We conducted a nested case-control study in California that included CP cases from a statewide system on developmental disabilities and randomly selected 20 % births without CP as controls during 2005-2015. Gestational weekly-average temperatures were calculated from high-resolution (1 km) daily mean temperatures at the maternal residential address at birth. We implemented a distributed lag model within a logistic framework to estimate the associations between per 5 °C increase of temperature, extreme heat that above the 90th percentile of the local temperature distribution, and CP risk in gestational week 0-31 and final seven weeks preceding birth. Further, we performed a sibling analysis to consider the influence of uncontrolled confounding. RESULTS: The study population included 5938 CP cases and 1,092,313 controls. There was an increased risk of CP associated with per 5 °C increase of weekly ambient temperature (odds ratio, ORs: 2 %, 95 % credible interval: 1 %-5 %) or extreme heat (ORs of 4-5 %, 95 % credible interval: 0 %-13 %) in the early pregnancy. Stronger associations were observed if such exposures happened cumulatively over time (ORs of 8 %-18 %). A similar trend was also suggested in the sibling analyses. CONCLUSIONS: Early-pregnancy exposure to high ambient temperature was associated with increased risk of childhood CP. Our findings urge further monitoring of childhood neurodevelopmental disorders in the context of changing climate.