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Human Fetal and Cord Serum Thyroid Hormones: Developmental Trends and Interrelationships

Maternal and Child Health Sciences (R.H., J.S., C.D.) and Community Health Sciences (F.L.R.W.), University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom; Department of Internal Medicine (H.v.T., T.J.V.), Erasmus University Medical School, 3000 DR Rotterdam, The Netherlands; and Nuclear Medicine Service (S.Y.W.), Veterans Affairs Medical Center, University of California–Irvine Medical Center, Long Beach, California 90822-5201

Address all correspondence and requests for reprints to: Professor Robert Hume, Maternal and Child Health Sciences, University of Dundee, Ninewells Hospital, and Medical School, Dundee DD1 9SY, Scotland, United Kingdom. E-mail: r.hume{at}dundee.ac.uk.

Thyroid hormone is essential for fetal and neonatal development in particular of the brain, but little is known about regulation of fetal thyroid hormone levels throughout human gestation. The purpose of this study was to clarify developmental trends and interrelationships among T₄, free T₄ (FT4), thyroxine-binding globulin (TBG), TSH, T₃, rT₃, and T₄ sulfate (T4S) levels in cord and fetal blood sera (n = 639, 15–42 wk gestation) and correlate infant levels (23–42 wk gestation) to maternal values (n = 428, 16–45 yr) and those of nonpregnant women (n = 233, 16–46 yr). In cord and fetal serum, T₄, T₃, and TBG levels increase with gestation until term; TSH, FT4, T4S, and rT₃ levels increase and peak in the late second/early third trimester and then decline to term; T₄/TBG ratios increase until late second trimester and plateau to term. Term cord sera TSH, TBG, and all iodothyronine levels, except T₃, are higher than nonpregnant women. In the third trimester, cord serum FT4, TSH, rT₃, and T4S levels are also higher than corresponding maternal levels, but T₄, T₃, and TBG levels are lower than maternal values. The late second/early third trimester is a critical transition period in fetal thyroid hormone metabolism, which may be interrupted by preterm birth and contribute to postnatal thyroid dysfunction.

This work was supported by Commission of European Community (QLG3-2000-00930), Chief Scientist’s Office Scottish Executive (K/MRS/50/C741), Wellcome Trust, Tenovus (Scotland), and Paediatric Metabolic Fund.

Abbreviations: FT4, Free T₄; SULT, sulfotransferase; TBG, thyroxine-binding globulin; T4S, T₄ sulfate.

¹ For a list of members of the Scottish Preterm Thyroid Group, see Acknowledgments.

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