Association between prenatal exposure to residential pyrethroid insecticides and congenital hypothyroidism using propensity score matching.

This study aimed to assess the relationship between exposure to Type II pyrethroids and congenital hypothyroidism (CH), particularly in leishmaniasis-endemic regions where the immunity of residents is compromised.In this population-based case-control study, we used all mothers and newborns secondary data for the period 2017-2022 in eastern Isfahan province. Cases were newborns confirmed with diagnosis of CH. Data of insecticides spraying and fogging facilitated the identification of affected and unaffected regions. Propensity score (PS) matching was applied for matching controls to cases (5:1). The descriptive information reported along with the mapping generated using ArcGIS 10.8.2. Trimester-Specific analyses were conducted using STATA 17 with adjusting for possible confounders.After PS matching, out of 37,085 mother-newborn pairs registered in national Integrated Health System, 744 were included in the final analysis. After adjustment for birth and maternal characteristics, the association strengthened for second-trimester exposure (OR adjusted = 3.00; 95% CI: 1.13-7.93), reaching statistical significance. A significant association was observed between cumulatively pyrethroid exposure with CH and strengthened after adjustment (OR adjusted = 2.33; 95% CI: 1.22-4.45).Our findings revealed that maternal exposure to type II pyrethroid insecticides during pregnancy, particularly in the second trimester, may increase the risk of CH.