Association of hypothyroidism during pregnancy with preconception and early pregnancy exposure to ambient particulate matter.

Background: Limited research has been conducted on the association between preconception exposure to ambient particulate matter (PM) and hypothyroidism. This study aimed to investigate the relationship between preconception PM exposure and hypothyroidism.

Methods: A retrospective case-control study at China-Japan Friendship Hospital was performed. Fine particulate matter (PM) and inhalable particulate matter (PM) were obtained from the China High Air Pollution Dataset. Buffer analysis methods were used to calculate the exposure of pregnant women to PM in a circular area of 250, 500, and 750 m in diameter at preconception and in early pregnancy. Logistic regression models were used to assess the relationship between PM and hypothyroidism. Odd ratios (ORs) and 95% confidence intervals (CIs) were used to evaluate the effect of PM on the risk of hypothyroidism.

Results: A total of 3,180 participants were studied, and they comprised 795 hypothyroid patients and 2,385 matched controls. The mean age was 31.01 years (standard deviation: 3.66) in the control group and 31.16 years (standard deviation: 3.71) in the case group. Logistic regression analysis showed that exposure to PM and PM in the 60-day period before the last menstrual period month (LMPM), 30-day period before the LMPM, and LMP, across all distance buffers, was associated with an increased risk of hypothyroidism (all P < 0.05). The most pronounced effect was observed during the LMPM, with PM (OR: 1.137, 95% CI: 1.096-1.180) and PM (OR: 1.098, 95% CI: 1.067-1.130) in the 250-m buffer. Subgroup analysis in the Changping District yielded consistent results with the main analysis.

Conclusion: Our study shows that preconception PM and PM exposure increases the risk of hypothyroidism during pregnancy.