Effects of mild insufficient iodine intake on thyroid function and autoantibodies in pregnant women

Objective To investigate the effects of mild insufficient iodine intake on thyroid function and autoantibodies in pregnant women, and to provide a basis for scientific supplementation of iodine to pregnant women. Methods From December 2015 to March 2016, Suixi County in Guangdong Province was selected as a survey site, Lechang City as a control site, local pregnant women and 8 to 10 years old students were selected as study subjects. Urinary iodine, thyroid function and 5 autoantibodies of the pregnant woman were tested: thyrotropin (TSH) and free thyroxine (FT4), free triiodothyronine (FT3), anti-thyroid peroxidase (TPOAb) and anti-thyroglobulin (TgAb). Student’s intelligence was determined. Automatic chemiluminescence method was used to test 3 items of thyroid function and TPOAb, TgAb was tested by antigen-antibody combining, the level of urinary iodine was detected by the method of inductively coupled plasma mass spectrometer, and student’s intelligence was determined by China joint raven's test. Results The median urinary iodine of the investigation group and control group in pregnant women was 113.0 and 172.1 μg/L, respectively, the difference was statistically significant (Z =-9.37, P < 0.05). The TSH median of early, mid and late pregnant women in the investigation group was 0.89, 1.23 and 1.18 mU/L, mean of FT4 was 16.61, 14.74 and 14.19 pmol/L, mean of FT3 was 4.88, 4.18 and 3.91 pmol/L, respectively. The TSH of the control group was 0.81, 1.12 and 1.39 mU/L in early, middle and late pregnancy women, FT4 was 17.02, 14.71 and 15.21 pmol/L, and FT3 was 4.89, 4.26 and 4.25 pmol/L, respectively. No difference was found between the two groups of the three kinds of hormone levels in pregnant early and mid pregnancy (TSH: Zearly =-0.36, Zmid =-0.33, P = 0.72, 0.74; FT4: tearly =-0.82, tmid =-0.09, P = 0.41, 0.93; FT3: tearly =-0.11, tmid =-1.45, P = 0.91, 0.15), in late pregnancy FT4 and TSH were lower than those of control group (Z =-3.03, P < 0.05; t =-2.34, P < 0.05). The incidence of thyroid dysfunction was 13.6% (40/293) and 10.8% (32/296) in the investigation and control pregnant women, respectively, no statistical difference was found (χ2 = 1.11, P = 0.29); the incidence of low FT4 hematic disease was all 0.3%, and no significant difference was found (χ2 = 0.00, P = 1.00); the thyroid dysfunction incidence rates were 1.0% (3/293) and 0.3% (1/296), respectively, also no statistical difference was found (χ2 = 1.03, P = 0.37). Thyroid autoantibodies positive rate of the investigated pregnant women and the control was 12.0% (40/333) and 10.6% (35/331), respectively, no statistical difference was found (χ2 = 0.34, P = 0.56). The IQ scores of investigated and control groups were 105.0 and 106.6, respectively, and there were significantly different (t =-2.64, P < 0.05), but the distribution of intelligence quotient was not different (χ2 = 8.93, P = 0.18). Conclusions Urine iodine median of Suixi pregnant women is in 100-149 μg/L level, which has no significant effect on thyroid function and autoantibodies, but FT4 levels are lower than those of the control group, which merit attention. We suggest that pregnant women in similar regions to supplement iodine in order to make urinary iodine level of pregnant women reaching the level of 150 μg/L recommended by WHO. Key words: Iodine; Pregnant women; Thyroid function