[Thyroid function and thyroid autoimmunity at the late pregnancy: data from 664 pregnant women]

To study the prevalence of thyroid diseases, as well as characteristics of the disease spectrum and thyroid autoimmunity in women at the end of pregnancy.

Six hundred and sixty-four pregnant women (pregnancy group) and 276 non-pregnant women (control group) were enrolled in the study. Serum thyrotropin (TSH), thyroid peroxidase antibody (TPOAb), free T(3) (FT(3)) and free T(4) (FT(4)) were measured by high-sensitive immunochemiluminescent assay, and urinary iodine was also examined at the end of pregnancy. Overt hyperthyroidism was diagnosed when both TSH < 0.3 mU/L and FT(4) and/or FT(3) levels were elevated. Subclinical hyperthyroidism was diagnosed when TSH < 0.3 mU/L with normal FT(4) and FT(3) levels. The diagnostic criteria for overt hypothyroidism was TSH > 4.8 mU/L accompanied by decreased FT(4), and for subclinical hypothyroidism was TSH > 4.8 mU/L with normal FT(4) and FT(3) levels.

(1) The median urinary iodine (MUI) of pregnancy group was 201.5 microg/L, and that of control group was 196.0 microg/L (P > 0.05). Women in the two groups were iodine-adequate. (2) The overall prevalence of thyroid diseases in pregnancy group and control group was 7.8% (52/664) and 6.9% (19/276), respectively (P > 0.05). (3) As for the diseases pattern, there were obvious differences between the two groups. In pregnancy group, the prevalence of hyperthyroidism was lower than that of hypothyroidism (1.1% vs 6.8%, P < 0.01). In control group, the prevalence of hyperthyroidism and hypothyroidism was 4.7% and 2.2%, respectively (P > 0.05). Compared with control group, the prevalence of hyperthyroidism in pregnancy group was much lower (1.1% vs 4.7%, P < 0.01), mainly due to the decrease of overt hyperthyroidism; whereas, the increment of subclinical hypothyroidism resulted in the higher prevalence of hypothyroidism in pregnancy group (6.8% vs 2.2%, P = 0.01). (4) The median TSH level of the healthy women in pregnancy group was significantly higher than that in control group (2.50 vs 1.54 mU/L, P < 0.01). The positive rate of TPOAb in pregnancy women was lower than that in non-pregnancy women (3.3% vs 9.4%, P < 0.01).

At the end of pregnancy, hypothyroidism accounts for most thyroid diseases. Thyroid autoimmunity is suppressed.