Association between Maternal Hypothyroidism and Miscarriage Risk: A Community Based Cohort Study

Introduction: Maternal hypothyroidism is a frequent endocrine disorder during pregnancy and has been increasingly associated with miscarriage. However, many previous studies were limited by hospital based populations and insufficient control for psychological and medical confounders. This study aimed to assess the relationship between maternal hypothyroidism and miscarriage using a large communitybased cohort. Methods: Data were extracted from the Sina Electronic Health Record System covering 66279 pregnant women receiving prenatal care across health centers affiliated with Mashhad University of Medical Sciences (2017–2025). Thyroid status, pregnancy outcomes, psychological factors (depression, anxiety, domestic violence), and comorbidities were recorded. Univariate and multivariate logistic regression models were used to estimate adjusted odds ratios (AOR) with 95% confidence intervals (CI). Results: Maternal hypothyroidism was identified as a significant independent predictor of miscarriage (AOR = 1.60; 95% CI: 1.51–1.70; p < 0.001). Several additional risk factors showed strong independent associations, including advanced maternal age (AOR = 1.75 for 30–40 years; AOR = 1.90 for > 40 years; p < 0.001), Iranian nationality (AOR = 5.30; p < 0.001), residence in small cities (AOR = 2.23; p < 0.001) or suburban areas (AOR = 1.99; p < 0.001), and high parity (AOR = 3.20 for second pregnancy; 6.60 for third; 12.24 for ≥ 4 pregnancies; all p < 0.001). Psychosocial factors such as domestic violence (AOR = 1.25; p < 0.001), depression (AOR = 1.17; p < 0.001), and anxiety (AOR = 1.19; p < 0.001) were also associated with increased miscarriage risk. Medical comorbidities including obesity (AOR = 1.19; p < 0.001), diabetes (AOR = 1.21; p < 0.001), hypertension (AOR = 1.51; p < 0.001), cancer history (AOR = 1.40; p < 0.001), and genitourinary disorders (AOR = 1.37; p < 0.001) further contributed to risk. Conclusion: Maternal hypothyroidism is a significant and potentially modifiable risk factor for miscarriage. Our findings support the need for early thyroid screening during pregnancy, particularly in populations with high prevalence of thyroid disorders. Personalized management rather than universal treatment of mild subclinical hypothyroidism may offer more beneficial outcomes. Future research should examine treatment timing, autoantibody status and fetal developmental markers to develop clearer clinical guidelines.