Correlation between iodine nutritional status and thyroid hormone levels of pregnant women in Guanshan Lake District of Guiyang / 中华地方病学杂志

ABSTRACT

Objective To investigate the relationship between iodine nutritional status and thyroid hormone levels,and to provide a guideline for monitoring iodine nutrition and thyroid function.Methods A crosssectional survey was performed by randomly selecting 341 samples (health pregnant women with a first child) from the Second People's Hospital of Guiyang,Bihai Community Medical Center and Jinhuayuan Community Center from October 2015 to September 2016.Levels of serum hormones and antibodies relative to throid of pregnant women in Guanshan Lake District of Guiyang at different pregnant times,which included throid stimulating hormone (TSH),free three triiodothyronine (FT3),free thyroxine (FT4),thyroid peroxidase antibody (TPOAb),and thyroglobulin antibody (TgAb),were measured by the electrochemical luminescence method,and urinary iodine levels were measured by heat digestion.Results The median urinary iodine of pregnant women at early,middle and late stages (T1,T2 and T3 stages) were 191.8,198.9 and 214.5 μg/L,respectively.FT3 increased first and then decreased during pregnancy.Levels of FT3 in the T2 stage were significandy higher than those in T1 and T3 stages (FT3 medians at the three stages were 4.49,4.83 and 4.57 pmol/L),and the differences were statistically significant (P ＜ 0.05).FT4 levels decreased during pregnancy (FT4 medians at the three stages were 16.32,14.65 and 13.22 pmol/L),and the differences among the three groups were statistically significant (H =67.517,P ＜ 0.01).Statistically significant differences were not found in the TSH levels among the three groups ~SH medians at the three stages were 2.05,2.01 and 2.39 mU/L,H =1.297,P ＞ 0.05).The medians of TPOAb and TgAb during T2 stage (9.60 and 19.02 U/ml) were significantly lower than those of other groups (18.92 and 24.75 U/ml at stage T1,and 13.46 and 22.06 U/ml at stage T3),and the differences were statistically significant (P ＜ 0.05).TSH levels were consistent with urinary iodine levels.TSH levels in the excessive iodine group (urine iodine250 ～ 499 μg/L,2.54 mU/L) were significantly higher than those in the adequate iodine group (urine iodine150 ～ 249 μg/L,1.97 mU/L) and deficient iodine group (urine iodine＜ 150 μg/L,1.91 mU/L),and the differences were statistically significant (P ＜ 0.05).No correlations were found between levels of FT3,FT4,TPOAb,TgAb and levels of the urinary iodine.There was a significant positive correlation between urinary iodine levels and TSH levels (rs =0.180,P ＜ 0.01).The incidence of abnormal thyroid function in pregnant women was 29.33％ (100/341),which was composed of clinical hypothyroidism (accounting for 0.88％,3/341),subclinical hypothyroidism (accounting for 25.51％,87/341),low T4 level (accounting for 1.76％,6/341),clinical hyperthyroidism (accounting for 0.59％,2/341),subclinical hyperthyroidism (accounting for 0.59％,2/341),and TPOAb positive and TgAb positive (accounting for 12.61％,43/341).These abnormalities occurred mainly in the T1 and T3 stages.The prevalence of subclinical hypothyroidism increased with increasing of urinary iodine level,and the difference was statistically significant (x2 =11.269,P ＜ 0.05).Conclusion There is a positive correlation between pregnancy iodine nutritional status and its TSH level,so it is important to monitor the level of urinary iodine during pregnancy and to screen the thyroid function and antibodies in the early and middle time of pregnancy.