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Thyroid function and thyroid size in normal pregnant women living in an iodine replete area
Author(s) -
Berghout Arie,
Endert Erik,
Ross Alec,
Hogerzeil Hendrlkus V.,
Smits Nico J.,
Wlerslnga Wilmar M.
Publication year - 1994
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/j.1365-2265.1994.tb02560.x
Subject(s) - pregnancy , thyroid , medicine , endocrinology , thyroid function , iodine deficiency , iodine , thyroid function tests , hormone , free thyroxine , chemistry , biology , genetics , organic chemistry
Summary OBJECTIVE The interpretation of the changes in thyroid hormone concentrations during normal pregnancy is a matter of debate involving, in some geographical regions, enhanced thyrold activity in early pregnancy and a hypothyroid state In the third trimester. A clinically detectable increase in thyroid size has been found in areas of mild iodine deficiency ('goitre of pregnancy'), but not in iodine replete areas. DESIGN A prospective study. We have studied thyroid size and function In normal pregnant women living In an iodine replete area. PATIENTS Healthy women before and during a normal pregnancy resulting from artificial Insemination ( n = 10) and other women during the normal menstrual cycle ( n = 11), in the iodine replete area of Amsterdam. MEASUREMENTS Thyroid volume was measured by ultrasonography. Plasma T4, free T3, free reverse T3, TSH, thyroxine binding globulln, hCG, progesterone and thyroid autoantibodies were measured. RESULTS Thyroid volume did not change during prep nancy (data given before pregnancy and during lst, 2nd and 3rd trimesters, respectively: 10·3 ± 5·1, 10·6 ±4·4, 9·6 ± 3·8 and 9·4 ±3·0 ml, NS). Free T4 and free T3 levels declined during pregnancy (13·7±2·0, 13·5 ±4·1, 11·2 ±2·8, 10·2 ±1·6pmol/l, P = 0·005; 4·55 ±0·63, 4·64 ± 0·88, 3·72 ± 0·67 and 4·01 ± 0·75pmol/l, P = 0·003), whereas free reverse T3 levels increased during pregnancy (0·16 ± 0·04, 0·19 ± 0·07, 0·14 ±0·03 and 0·20 ± 0·07pmol/l, P = 0·001). Thyroglobulin levels remained unchanged. Thyroid hormones and thyroid volume did not differ between folllcular and luteal phases of the menstrual cycle. CONCLUSION Thyrold volume does not increase during pregnancy in iodlne‐replete areas. The decrease in free T4 and free T3 and the Increase in free reverse T3 concentrations during pregnancy resemble the changes in thyroid hormones seen in non‐thyroidal illness. This could be a physiologlcal adaptation enabling energy conservation durlng the high metabolic demands of pregnancy.