Gestational month-specific reference ranges for TSH and thyroxine in Han nationality women in iodine sufficient area of China / 中华内分泌代谢杂志

ABSTRACT

Objective To establish the gestational month-specific reference intervals for thyrotropin and thyroxine in Han nationality women in iodine sufficient area of China. Methods In iodine sufficient area of China, 120 non-pregnant women and 1 118 pregnant women at gestational ages from 4 to 36 week (4 weeks≈1 month) were collected according to the strict criteria. Urinary iodine excretion and serum thyrotropin (TSH), total thyroxine (TT4), free thyroxine (FT4), thyroid peroxidase antibody (TPOAb) levels were determined in all subjects. Results During pregnancy, serum TSH increased at week 4, and then began to decrease with the lowest level at week 12, which was 35% lower than the non-pregnant level." After that, serum TSH increased gradually and finally became stable during the third-trimester of pregnancy (T3) when the level was 29% higher than that of non-pregnant controls. Serum TT4 elevated dramatically during the first-trimester with peak at week 16, which increased by 70% compared with the non-pregnant level, then slightly decreased, and became steady with 50% increasing compared with non-pregnant level. Serum FT4 initially increased slightly with peak at week 4, and then decreased gradually until the beginning of T3 without obvious fluctuation during T3. Conclusion The gestational month-specific reference intervals for TSH, TT4 and FT4 are necessary for the early diagnosis of maternal subclinical hypothyroidism and hypothyroxinaemia.