[Evaluation of thyroid function during pregnancy: first-trimester reference intervals for thyroid-stimulating hormone and free thyroxine].
OBJECTIVE
The physiological changes that occur during pregnancy affect the physiology of the thyroid gland. Consequently, interpretation of thyroid function markers during pregnancy requires trimester-specific reference intervals. The aims of our study were to: 1) establish first-trimester reference intervals for biochemical markers of thyroid function [thyroid-stimulating hormone (TSH) and free thyroxine (T4)] and 2) to establish the prevalence of autoimmune thyroid disease in pregnant women resident in Cartagena (Murcia, Spain).


METHODS
A total of 441 women between weeks 11 and 13 of pregnancy were included in this study. A blood sample was extracted from all women to measure TSH, free T4 and antithyroid antibodies. Reference intervals for TSH and free T4 were determined in 400 pregnant women without autoimmune thyroid disease or known thyroid disease.


RESULTS
Autoimmune thyroid disease was detected in 23 pregnant women (5.2%) who showed TSH levels higher than those in pregnant women without thyroid autoimmunity. First-trimester reference intervals were as follows: TSH: 0.130-3.710 mUI/L; free T4: 0.89-1.50 ng/dL. These reference intervals differed from the non-pregnant reference intervals used in our laboratory.


CONCLUSIONS
The reference intervals established are useful to evaluate thyroid function in women between 11 and 13 weeks of pregnancy. Interpretation of thyroid function requires intervals established in a reference population without autoimmune thyroid disease and with the methodology usually used to analyze these markers.
García de Guadiana Romualdo
Luis
L
Clínica Militar, Hospital Naval Cartagena, Cartagena, Murcia, España. guadianarom@yahoo.es
González Morales
Mercedes
M
Martín-Ondarza González
María del Carmen
Mdel C
Martín García
Elena
E
Martínez Uriarte
Juan
J
Blázquez Abellán
Ana
A
Nuevo García
Jorge
J
D000293:Adolescent; D000328:Adult; D001327:Autoimmune Diseases / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008875:Middle Aged; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology*; D011261:Pregnancy Trimester, First; D015995:Prevalence; D012016:Reference Values; D013959:Thyroid Diseases / Q000453:epidemiology* / Q000276:immunology*; D013961:Thyroid Gland; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D055815:Young Adult
D013972:Thyrotropin; D013974:Thyroxine