Spatial variation and association between maternal chemical fertilizer exposure and preterm birth in a rural area in Northern China.

Whether maternal macro-environmental chemical fertilizer exposure has an association with the risk of preterm birth remains unclear. This study aimed to investigate the association between maternal exposure to chemical fertilizer during pregnancy and the risk of preterm birth. A total of 13,861 births, including 402 preterm birth from 313 villages in Pingding County, Shanxi Province, China, were analyzed to explore spatial variations of preterm birth risks at the village level. Spatial variations of preterm birth were visualized and tested with Disease Mapping, Moran's I and G* Statistic. The spatial zero-inflated negative binomial model was used to evaluate the incidence rate ratio (IRR) of preterm birth in different chemical fertilizer consumption levels at the village level. A population-based case-control study was conducted including 153 preterm births cases and 204 controls at the household level. The two-level logistic regression model was performed to estimate the association between risks of preterm birth and maternal exposure to chemical fertilizer after adjusting confounding factors. The findings indicated a remarkably clustering effect in relative risks of preterm birth and identified a high-risk clustering region of preterm birth from the south-central to the southwest and a low-risk clustering region in the northern Pingding county. The results of the spatial zero-inflated negative binomial model showed that the risk of preterm birth in the villages with chemical fertilizer consumption≥100 tons was 2.82 (95% CI: 1.50-5.57) times higher than those with <50 tons. Maternal exposure to chemical fertilizer ≥100 tons at village level was associated with an increased risk of preterm birth (aOR 2.14, 95%CI: 1.18-3.96), compared with exposure <50 tons after adjusting for confounding variables. The findings suggests that chemical fertilizers deserve more attention as a potential risk factor of preterm birth.