High Prevalences of Subclinical Hypothyroidism and Positive Thyroid Autoantibodies Recorded Among Women of Childbearing Age in China: National Cross-Sectional Study

Abstract

Background: Iodine deficiency and thyroid disorders are associated with several obstetric and neonatal adverse outcomes. Mandatory universal salt iodization in China was implemented 20 years ago; however, the current iodine status and prevalence of thyroid disorders among women of childbearing age are unknown. Methods: A nationally representative cross-sectional study with 26166 enrolled participants aged 18 to 49 years from all 31 provincial regions of mainland China was performed. The participants were given a questionnaire and underwent B-mode ultrasonography of the thyroid. The serum concentrations of thyroid hormones and thyroid antibodies and the urine iodine concentration (UIC) were measured. Findings: The median UIC was 178.7 μg/L, which is indicative of adequate iodine status; however, 19.04% and 19.87% of the participants were classified as having iodine deficiency and excessive iodine, respectively. The weighted prevalences of thyroid disorders were as follows: 1.08% had overt hyperthyroidism, 0.58% had subclinical hyperthyroidism, 0.76% had Graves’ disease, 1.28% had overt hypothyroidism, 14.28% had subclinical hypothyroidism, 13.53% were positive for TPOAb, and 14.55% were positive for TgAb. Excessive iodine and overweight were associated with higher odds of subclinical hypothyroidism. A family history of thyroid disorders and an age between 40 and 49 years were significantly associated with higher odds of positivity for TPOAb and positive TgAb. At the provincial level, the prevalences of iodine deficiency, excessive iodine, subnormal TSH levels, and supranormal TSH levels varied widely. Gansu was identified as a region with high prevalences of both excessive iodine and supranormal TSH levels. Interpretation: Iodine deficiency, excessive iodine, subclinical hypothyroidism, and positivity for thyroid autoantibodies are still prevalent among women of childbearing age in China. Women of childbearing age who are relatively older, have excessive iodine, are overweight, or have a family history of thyroid disorders are encouraged to undergo active screening of their UIC and thyroid function when planning a pregnancy. Strategies for addressing iodine status and thyroid disorders require geographic targeting of this subpopulation. Funding Statement: National Health Commission of the People’s Republic of China and National Natural Science Foundation of China. Declaration of Interests: The authors declare no conflict of interests. Ethics Approval Statement: The research protocols were approved by the Medical Ethics Committee of China Medical University.