title: Maternal thyroid function in early and late pregnancy.
abstract: Thyroid function was investigated during and after pregnancy in 12 healthy euthyroid women. During pregnancy, serum total T4 (TT4) levels were significantly elevated and nearly stable, while thyroxine-binding globulin (TBG) levels progressively increased till the 7th month. A slight elevation, though not significant, of free T4 (fT4) was recorded in early pregnancy. In the following months, fT4, free T3 (fT3) and the T4/TBG ratio progressively diminished, reaching a plateau at the 7th month. Serum TSH levels, measured by an ultrasensitive immunofluorometric assay, were comparable to postpartum values during the first trimester and showed a moderate upward trend with the progression of pregnancy. The evaluation of 24-hour TSH profiles was performed in 5 women during the first trimester of pregnancy. In all women, the circadian rhythm of TSH was present with a normal nocturnal surge, though anticipated in 1 case. In summary (1) during the first trimester of pregnancy, the increased thyroid activity does not seem to be only sustained by pituitary TSH which remains unmodified; the negative correlation between TSH and hCG levels might suggest that hCG also stimulates the gland to increase thyroid hormone output, and the presence of a normal TSH circadian rhythm indicates that the central mechanism of neuroregulation of the pituitary-thyroid axis is preserved in early pregnancy, and (2) in late pregnancy, a marked decrease in free thyroid hormone fractions is accompanied by serum TSH levels still in the normal range, indicating a modification of thyroid homeostasis which might recognize various etiological factors.
authors.affiliation: Italian Auxologic Center, IRCCS, University of Milan.
authors.forename: M
authors.initials: M
authors.lastname: Nissim
authors.forename: G
authors.initials: G
authors.lastname: Giorda
authors.forename: M
authors.initials: M
authors.lastname: Ballabio
authors.forename: A
authors.initials: A
authors.lastname: D'Alberton
authors.forename: D
authors.initials: D
authors.lastname: Bochicchio
authors.forename: R
authors.initials: R
authors.lastname: Orefice
authors.forename: G
authors.initials: G
authors.lastname: Faglia
mesh_terms: D000328:Adult; D006063:Chorionic Gonadotropin / Q000097:blood; D002940:Circadian Rhythm; D005260:Female; D006801:Humans; D049590:Postpartum Period / Q000502:physiology; D011247:Pregnancy / Q000502:physiology*; D013961:Thyroid Gland / Q000502:physiology*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D013975:Thyroxine-Binding Proteins / Q000378:metabolism; D014284:Triiodothyronine / Q000097:blood
chemical_list: D006063:Chorionic Gonadotropin; D013975:Thyroxine-Binding Proteins; D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine