Thyroid disease screening in early pregnant women after implementation of a new standard of salt iodine content in Hangzhou

Objective To establish a normal reference range of thyroid-related indicators of early pregnant women in Hangzhou, and investigate the prevalence of thyroid disease among them after the implementation of a new standard of salt iodine content, in order to provide reference for monitoring of thyroid disease in pregnant women. Methods A total of 582 women in early pregnancy (0-13 weeks of gestation) in Hangzhou were selected via the stratified random sampling method as the subjects of the study and for detection of serology thyroid function. The levels of serum thyroid stimulating hormone (TSH), free thyroxine (FT4), thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb) were measured by chemiluminescence method. According to the standard American Academy of Clinical Biochemistry (NACB), 359 women in early pregnancy were strictly screened to establish the normal reference value of TSH, FT4, and the reference range using the 95% confidence interval (95%CI). At the same time, the newly establish reference interval was used to evaluate the thyroid function of 582 early pregnant women. Results The reference interval of TSH in early pregnant women of Hangzhou was 0.048-3.354 mU/L. The reference interval of FT4 was (13.023 ± 3.316) pmol/L, and the tenth percentile of FT4 was 11.030 pmol/L. Eighty-four persons' thyroid function was abnormal in 582 and the rate of abnormal was 14.4% (84/582), in which the rates of abnormal in clinical hypothyroidism, subclinical hypothyroidism, subclinical hyperthyroidism and hypothyroxinemia were 0.2% (1/582), 3.4% (20/582), 1.9% (11/582) and 8.9% (52/582), respectively. The case with clinical hyperthyroidism was not detected. The positive rate of TPOAb and TgAb were 10.8% (63/582) and 11.7% (68/582). The abnormal rate of hypothyroxinemia and the positive rate of TPOAb in early pregnant women in the city (11.4%, 13.5%) were significantly higher than that in the rural areas (6.3%, 8.1%, χ2= 4.708, 4.309, P < 0.05). Conclusions The normal reference value of thyroid hormones in early pregnant women in Hangzhou is established, and it is found that the incidence of thyroid disease is higher in pregnant women in Hangzhou after the implementation of the new standard of salt iodine content, therefore, it is imperative to carry out monitoring (or screening) of thyroid function in early pregnant women. Key words: Salts; Iodine; Early pregnancy; Reference value; Thyroid disease