Reference intervals for thyroid hormones in pregnant Chinese women

Ann Clin Biochem. 2001 Jul;38(Pt 4):329-32. doi: 10.1258/0004563011900830.


Objective: To establish gestation-related reference intervals for thyroid hormones in a Chinese population.

Materials and methods: A prospective study with 343 healthy pregnant women (5-41 weeks) and 63 non-pregnant controls. Thyroid stimulating hormone (TSH), free thyroxine (T4) and tri-iodothyronine (T3) (and human chorionic gonadotrophin) were measured by immunoassays. The median, 2.5th and 97.5th percentiles at 4-week intervals were calculated. Data were also analysed for significant trends using ANOVA.

Results: Free T3 decreased during pregnancy, whereas free T4 initially increased, peaking between 9-13 weeks and then decreased, the decline becoming significant by week 21. TSH mirrored changes in free T4.

Conclusion: The gestation-related reference intervals for thyroid hormones should alleviate the misinterpretation of thyroid function in pregnancy.

Publication types

  • Comparative Study

MeSH terms

  • Adult
  • Analysis of Variance
  • Asians
  • China
  • Chorionic Gonadotropin / blood
  • Female
  • Humans
  • Immunoassay / methods
  • Middle Aged
  • Pregnancy / blood*
  • Pregnancy Trimester, First
  • Pregnancy Trimester, Second
  • Reference Values
  • Thyrotropin / blood*
  • Thyroxine / blood*
  • Triiodothyronine / blood*


  • Chorionic Gonadotropin
  • Triiodothyronine
  • Thyrotropin
  • Thyroxine