Thyroid Dysfunction and Their Risk Factors among Pregnant Women: A Report from an Adequate Iodine Region

Introduction: Thyroid dysfunction, a common complication of pregnancy, is associated with adverse prenatal consequences. This study aimed to determine the prevalence of thyroid dysfunction and thyroid peroxidase antibody, and measure iodine level during the first trimester of pregnancy among Iranian women.Materials and Methods: In the first phase of a population-based cohort study, 418 pregnant women in their first trimester of pregnancy, and 438 non-pregnant women, were enrolled. Serum concentrations of TSH, FT4, FT3, TPO-Ab and urinary iodine concentrations, of all participants were measured. Results: During the first trimester of gestation, the prevalence of overt and subclinical hypothyroidism was 4.32%, 17.03%, respectively. The prevalence of overt and subclinical hyperthyroidism was 0.23%, 1.2 %, respectively. Among non–pregnant women, 2.1% had overt and 4.6% had subclinical hypothyroidism. The prevalence of subclinical and overt hyperthyroidism in non-pregnant women was 0.5% and 0.7%, respectively. Overall, 17.9 % of pregnant and 21.9% of non-pregnant women were positive for TPO-Ab. Positive TPO-Ab was a risk factor for hypothyroidism, in both pregnant and non-pregnant women (RR=2.325, P=0.003 and RR=6.359, P=0.001, respectively). The median (Interquartile range (IQR)) of urinary iodine concentration (UIC) in pregnant women was 154 μg/l (108.0-216.2 μg/l) and 169.0 μg/L (109.7 – 250.0 μg/l), respectively.Conclusions: We report high prevalence of hypothyroidism and positive TPO-Ab in pregnant and childbearing-age women, despite adequate iodine intake. There was a strong association between hypothyroidism and positive TPO-Ab. The role of high prevalence of autoimmunity should be investigated in future studies.