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Interpretation of in‐vitro thyroid function tests during pregnancy
Author(s) -
SMITH STEPHEN C. H.,
BOLD ALAN M.
Publication year - 1983
Publication title -
bjog: an international journal of obstetrics and gynaecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.157
H-Index - 164
eISSN - 1471-0528
pISSN - 1470-0328
DOI - 10.1111/j.1471-0528.1983.tb08962.x
Subject(s) - medicine , endocrinology , thyroid function , thyroxine binding proteins , pregnancy , thyroid , thyroxine binding globulin , hormone , thyroid function tests , reference range , globulin , free thyroxine , triiodothyronine , biology , genetics
Summary. In‐vitro thyroid function tests are difficult to interpret in pregnancy because of, among other things, the effect of oestrogens on thyroid binding globulin (TBG) concentrations. In an attempt to clarify the position, serum concentrations of total thyroxine (T 4 ), free T 4 , TBG, T 4 /TBG ratio, tri‐iodothyronine (T 3 ) and thyroid stimulating hormone (TSH) were measured. Total T 4 and TBG concentrations rose to above the non‐pregnant reference range by 20 weeks. The T 4 /TBG ratio fell to hypo‐thyroid values by 20 weeks but although the free T 4 level was lower in the third trimester compared with values in the first and second trimesters, only a few subjects had hypothyroid values. The TSH values remained unchanged throughout pregnancy. The significance of these changes is discussed and reference ranges for these hormones at each trimester are provided.