Association of thyroid dysfunction and autoantibody positivity with the risk of preterm birth: a hospital-based cohort study

BACKGROUND: Evidence for the association of thyroid dysfunction and autoantibody positivity with preterm birth remains controversial. We aimed to study the association of maternal thyroid dysfunction and autoantibody positivity with the risk of preterm birth. METHOD: A hospital-based cohort study of 40,214 women was conducted. Gestational age-specific percentiles of the FT4 and TSH concentrations were used for the definition of thyroid dysfunction. Autoantibody positivity was identified when the concentration > the threshold. The association of thyroid dysfunction and autoantibody positivity with the risk of preterm birth was estimated. RESULTS: No significant higher risk of preterm birth was found for women with variants of thyroid dysfunction or autoantibody positive than euthyroid women. Sensitivity and stratification analyses indicated that thyroperoxidase antibody (TPOAb) positivity in the first trimester (odds ratio [OR], 1.49; 95% confidence interval [CI], 1.17–1.90) and overt hypothyroidism restricted to women negative for TPOAb (OR, 4.94; 95%CI: 1.64–14.84) was associated with an increased risk of preterm birth. Modification effects of gestational age were found for women who had the test ≤18 and > 18 weeks. Continuous FT4 measurements tested ≤18 weeks of gestation were associated with a higher risk of preterm birth (OR, 1.13, 95% CI: 1.00–1.28), while a negative relationship for FT4 concentrations tested > 18 weeks of gestation (OR = 0.68, 95% CI: 0.48–0.97). CONCLUSIONS: Some specific thyroid function abnormalities were associated with an increased risk of preterm birth. Interaction between gestational age and FT4 concentration on the risk of preterm birth was identified, with a critical node of 18 weeks of gestation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12884-022-04806-9.