Establishment of reference range for thyroid hormones in normal pregnant Indian women

• Published in: BJOG : an international journal of obstetrics and gynaecology 2008-04, Vol.115 (5), p.602-606
• Main Authors: Marwaha, RK, Chopra, S, Gopalakrishnan, S, Sharma, B, Kanwar, RS, Sastry, A, Singh, S
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Electrochemiluminescence; Female; Gynecology. Andrology. Obstetrics; Hormones; Humans; India - ethnology; Medical sciences; Medical tests; Obstetrics; Parity; Pregnancy; Pregnancy Trimesters - blood; reference range; Reference Values; Thyroid gland; thyroid hormones; Thyroid Hormones - blood; trimester specific
• ISSN: 1470-0328; 1471-0528
• DOI: 10.1111/j.1471-0528.2008.01673.x

Background  Interpretation of thyroid function tests during pregnancy needs trimester‐related reference intervals from pregnant populations with minimal risk for thyroid dysfunction. While India has become iodine sufficient after two decades of salt iodisation, there is no normative data for thyroid function from healthy pregnant women of this country. Aims and objectives  To determine trimester‐specific reference ranges for free triiodothyronine (FT3), free thyroxine (FT4) and thyrotropin (TSH) from healthy pregnant Indian women. Design  Cross‐sectional study in a reference population of pregnant women. Setting  Primary care level obstetric department in India. Population  Women with uncomplicated pregnancy in any trimester. Methods  Five hundred and forty‐one apparently healthy pregnant women with uncomplicated single intrauterine gestations reporting to the Armed Forces Clinic in any trimester were consecutively recruited. Clinical examination, thyroid ultrasound for echogenicity and nodularity and estimation of FT3, FT4, TSH and antithyroid antibodies (antithyroperoxidase [anti‐TPO] and antithyroglobulin [anti‐Tg]) using electrochemiluminescence technique were carried out. From this entire sample, a disease‐ and risk‐free reference population was obtained by excluding those with any known factor that could affect thyroid function or those who were being treated for thyroid dysfunction. Main outcome measure  None. Results  Of the 541 consecutive pregnant women in different trimesters enrolled for the study, 210 women were excluded. The composition of reference population comprising 331 women was 107 in first trimester, 137 in second trimester and 87 in third trimester. The 5th and 95th percentiles values were used to determine the reference ranges for FT3, FT4 and TSH. The trimester‐wise values in the first, second and third trimesters were: FT3 (1.92–5.86, 3.2–5.73 and 3.3–5.18 pM/l), FT4 (12–19.45, 9.48–19.58 and 11.32–17.7 pM/l) and TSH (0.6–5.0, 0.44–5.78 and 0.74–5.7 iu/ml), respectively. Analysis of mean, median values for FT3, FT4 and TSH between each trimester showed no significant difference in FT3 and TSH values (95% CI). However, FT4 showed significant variation between trimesters with values decreasing with advancing gestational age (P value: first versus second = 0.015, first versus third = 0.003 and second versus third = not significant). Women with antibody positivity and hypoechogenicity of thyroid gland had significantly higher TSH valu