Thyroid hormones according to gestational age in pregnant Spanish women

Abstract

BackgroundThyroid function changes during pregnancy and maternal thyroid dysfunction have been associated with adverse outcomes. Our aim was to evaluate thyroid hormones levels in pregnant women resident in Aragon, Spain.FindingsSamples for 1198 pregnant women with no apparent thyroid disorders were analyzed, using paramagnetic microparticle and chemiluminescent detection technologies, in order to determine levels of thyroid stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), thyroid peroxidase antibodies (TPO-Ab), and thyroglobulin antibodies (Tg-Ab). Of the women in our sample, 85.22% had normal values for TPO-Ab and Tg-Ab and 14.77% had results revealing the presence of autoimmune diseases of the thyroid. The thyroid hormone reference values obtained according to gestational age (in brackets) were as follows: for free T3, values were 3.38 ± 0.52 pg/mL (<11 weeks), 3.45 ± 0.54 pg/mL (11-20 weeks), 3.32 ± 0.43 pg/mL (21-30 weeks), 3.21 ± 0.53 pg/mL (31-36 weeks), and 3.23 ± 0.41 pg/mL (>36 weeks); for free T4, values were 1.10 ± 0.14 ng/dL (<10 weeks), 1.04 ± 0.14 ng/dL (11-20 weeks), 0.93 ± 0.12 ng/dL (21-30 weeks), 0.90 ± 0.13 ng/dL (31-36 weeks), and 0.80 ± 0.21 ng/dL (>36 weeks); and for TSH, values were (μIU/mL): 1.12 ± 0.69 (<10 weeks), 1.05 ± 0.67 (11-20 weeks), 1.19 ± 0.60 (21-30 weeks), 1.38 ± 0.76 (31-36 weeks), and 1.46 ± 0.72 (>36 weeks).ConclusionPregnant women with normal antibody values according to gestational age had values for FT4 and TSH, but not for FT3, that differed to a statistically significant degree. The values we describe can be used as reference values for the Aragon region of Spain.

CONTROVERSIES IN ENDOCRINOLOGY: On the need for universal thyroid screening in pregnant women

“…Maternal hypothyroxinemia, defined as a decreased serum concentration of free T 4 (FT 4 ) with a normal TSH, is about 150 times more frequent than congenital hypothyroidism (3); it reflects an underactive thyroid gland, whose more frequent cause is the nutritional deficiency of iodine (42). On the other hand, between 5 and 14% of healthy pregnant women show detectable anti-peroxidase and/or anti-thyroglobulin Abs (6,43), which are associated with higher concentrations of TSH and lower FT 4 than pregnant women with negative thyroid autoimmunity (44). Regarding hyperthyroidism, prevalences of Grave's disease, with ranges between 0.1 and 1% (45), and transient gestational hyperthyroidism syndrome, with ranges between 1 and 3%, have been reported (46).…”

“…FT 4 index (FT 4 I) is a calculated ratio based on two estimates, namely an estimate of triiodothyronine (T 3 ) resin uptake and an immunoassay Given the significant changes in the concentrations of thyroid hormones throughout gestation (80), the ATA has recommended that the formulation of the reference values should be performed not only for each trimester of pregnancy but also for each specific geographical region (81) and probably also taking into account the importance of potential variations between the technical methods of measurement. In Spain, for example, different regional studies have been performed (43,82,83,84) aiming to determine the reference range for thyroid hormones in pregnant women. The recent ATA guideline recommends that in the absence of local reference values, the upper normal value for TSH in pregnant women should be 2.5 mUI/ml in the first trimester and 3 mUI/ml in the second and third trimesters.…”

Trimester-Specific Reference Interval for Thyroid Function Tests in Pregnant Filipino Women

“…15 The prevalence of TPOAb positivity (3.08%) in this study is lower than the worldwide prevalence of 12-23%. 9,13,14 One subject in her first trimester of pregnancy, and another subject in the second trimester were removed from the analysis due to overt hypothyroidism and hyperthyroidism respectively.…”

“…5 However, interpretation of thyroid function tests in pregnancy can be difficult due to some physiologic changes, which include (1) decreased TSH during the first trimester due to stimulatory effect of human chorionic gonadotropin (hCG) which has structural similarity with TSH; (2) increased thyroid binding globulin (TBG) due to estradiol and altered hepatic glycosylation decreasing its clearance; (3) increased urinary iodide excretion which can cause impaired thyroid hormone production in areas of marginal iodine sufficiency; and (4) alterations in the immune system, leading to the onset, exacerbation, or amelioration of an underlying autoimmune thyroid disease. 6 Studies in different parts of the world have been conducted to establish laboratory and method-specific thyroid function tests across 3 trimesters of pregnancy -in iodine-sufficient areas like the USA, 7 Switzerland, 8 Spain 9 and in iodine-insufficient areas like China 10 and Iran. 11 The Philippines is considered to no longer iodine deficient as reported by the Food and National Research Institute in 2013 with the exception of pregnant women.…”

Are TSH normal reference ranges adequate for pregnant women?

“…In general, the 97.5 th percentile of TSH for the 1 st trimester is located in two groups: according to the Architect, Beckman and Immulite platform, it is about 3.0 mIU/L, while according to Centaur and Roche it s close to 4 mIU/L It should be pointed out that only 4 of 27 studies, 2 of them using the Abbott Architect platform (23,24), one using te Immulite platform (25) and one the Centaur platform (2), showed values close to or below the cutoff of 2.5 mIU/L.…”