IRON DEFICIENCY, A RISK FACTOR FOR THYROID AUTOIMMUNITY DURING SECOND TRIMESTER OF PREGNANCY IN CHINA

Previous studies have reported an association between iron deficiency (ID) and increased thyroid peroxidase antibody (TPO-Ab) during early pregnancy. The objective of this study was to explore the relationship between ID and thyroid dysfunction, as well as thyroid autoantibodies, during the second trimester of pregnancy. A total of 1,592 pregnant women (13 to 28 weeks gestation) were enrolled in this cross-sectional study. According to serum ferritin (SF) concentrations, they were divided into ID (SF <20 μg/L) or non-ID (SF ≥20 μg/L) groups. Logistic regression analysis was used to evaluate the association between ID and subclinical hypothyroidism (thyroid-stimulating hormone [TSH] >4.0 mIU/L and free thyroxine [FT4] within the reference range) and thyroid autoimmunity. The prevalence of ID was 23.43% (373/1,592). Compared with the non-ID group, the ID group had lower FT4 levels (13.94 pmol/L [8.91 to 29.82 pmol/L] versus 14.63 pmol/L [8.22 to 47.24 pmol/L]; P<.001]) and higher TSH levels (1.85 mIU/L [0.01 to 7.84 mIU/L] versus 1.69 mIU/L [0.01 to 10.2 mIU/L]; P<.05). Logistic regression analysis confirmed ID as a risk factor for increased thyroglobulin antibody (TG-Ab) (odds ratio 1.974; 95% confidence interval 1.065, 3.657; P<.05), but not for subclinical hypothyroidism or increased TPO-Ab. ID is associated with increased TG-Ab during the second trimester of pregnancy. Abbreviations: BMI = body mass index; CV = coefficient of variation; FT4 = free thyroxine; Hb = hemoglobin; ID = iron deficiency; IDA = iron deficiency anemia; SF = serum ferritin; T3 = triiodothyronine; T4 = thyroxine; TAI = thyroid autoimmunity; TG = thyroglobulin; TG-Ab = thyroglobulin antibody; TPO = thyroid peroxidase; TPO-Ab = thyroid peroxidase antibody; TSH = thyroid-stimulating hormone.