Objective To set up the trimester-specific reference ranges of thyroid hormones for normal pregnant women to provide reference criteria for diagnosis, treatment and monitoring or screening of thyroid disease during pregnancy and related research. Methods A cross-sectional survey was conducted in pregnant and nonpregnant women in iodine sufficient areas. A total of 505 normal pregnant women and 153 normal non-pregnant women （as control） were selected for establishing trimester-specific reference ranges of thyroid hormones after rigorous screening through the survey questionnaire and laboratory tests. Thyroid hormones were measured by Bayer automated chemiluminescence immunoassay, and the reference range of each hormone was calculated as median （ the 50th percentile value） and two-sided limits （the 2.5th and 97.5th percentile values）. Results All women investigated were in iodine sufficient status within optimal urine iodine level. The serum TSH level during the 1 st trimester was obviously declined compared with that in the non-pregnant individuals （P 〈0.01 ）, and started to rise during the 2nd trimester, but was still not restored to non-pregnant level until the 3rd trimester. Serum FT4 and FT3 levels gradually decreased from the 2nd trimester to the 3rd （ P 〈 0.01 ）, and the TT4 and TY3 levels were markedly elevated since early pregnancy （P 〈 0. 01 ） and reached peak levels at the 2nd trimester approximately making up to 1.5 times of those in the non-pregnant individuals. Conclusion The thyroid hormone levels during pregnancy differ completely from those of the non-pregnant individuals, and also differ during different gestation periods. Therefore, to establish trimester-specific reference data of thyroid hormones during normal pregnancy may be important for clinical practice.
Chinese Journal of Endocrinology and Metabolism
Pregnancy ： Thyroid hormones ： Reference values