Objective: To evaluate thyroid function and iodine nutritional status for pregnant women from various regions of China by determining plasma levels of thyrotrophin( TSH), free triiodothyronine( FT3), and free thyroxine( FT4).
Methods: Plasma samples were obtained from pregnant women that participated in the 2010-2012 China National Nutrition and Health Survey. Plasma levels of TSH, FT3, and FT4 were determined by using an automated chemiluminescence immunoassay analyzer. Thyroid function was evaluated according to the determined levels.
Results: A total of 877 plasma samples collected from pregnant women residing in different regions of China wereanalyzed for levels of TSH, FT3, and FT4. The median TSH levels detected in the first, second, and third trimesters of pregnancy were 1. 56, 1. 84, and 1. 89 m IU/L, respectively. The median FT4 levels were 17. 21, 16. 29 and 16. 35 pmol/L, respectively. The median FT3 levels were 4. 70, 4. 39 and 4. 18 pmol/L, respectively. The rate of normal thyroid function for this cohort was 78. 1%, and for the pregnant women that resided in large cities the rate was 71. 2%. The most common type of abnormal thyroid function that was detected was subclinical hypothyroidism. It had an overall incidence of10. 5%, and those residing in regions of rural poverty had the highest rate( 14. 5%). The normal rate of thyroid function for adult pregnant women at the end of the trimester( 28-40 weeks) during pregnancy was significantly lower than that of the pregnant women in the first and second trimester.
Conclusion: The rate of normal thyroid function in pregnant women is low( less than 80%). Subclinical hypothyroidism is the main type of thyroid dysfunction during pregnancy. It should be continued to pay attention to the relationship between the high incidence of subclinical hypothyroidism and iodine nutritional status of pregnant women, especially subclinical hypothyroidism caused by insufficient iodine intake.
Keywords: free thyroxine; free triiodothyronine; pregnant women; thyroid function; thyrotrophin.