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Title: Longitudinal assessment of thyroid function in pregnancy.
Austin Authors: Ekinci, Elif I ;Lu, Zhong X;Sikaris, Ken;Bittar, Intissar ;Cheong, Karey Y;Lam, Que;Crinis, Nick ;Houlihan, Christine A 
Affiliation: Department of Endocrinology, Austin Health, Melbourne, Australia
Issue Date: 19-Jul-2013
Publication information: Annals of Clinical Biochemistry 2013; 50(Pt 6): 595-602
Abstract: Trimester-specific reference intervals (RIs) for thyroid function tests are lacking for Beckman Dxl 800 analysers. We aimed to establish RIs for thyroid stimulating hormone (TSH), free thyroxine (fT4) and to track intraindividual changes in thyroid function throughout pregnancy.One hundred and thirty healthy women without antithyroid peroxidase antibodies were followed longitudinally. Thyroid function was determined at trimester-1 (T1): 9-13 weeks; trimester-2 (T2): 22-26 weeks; trimester-3 (T3): 35-39 weeks and postpartum (PP): 8-12 weeks. A subgroup (n = 47) was used to track intraindividual changes using PP as non-pregnant state (baseline).For trimesters 1-3, TSH (median (2.5th, 5th, 95th and 97.5th percentile)) was 0.77 (0.03, 0.05, 2.33, 3.05), 1.17 (0.42, 0.47, 2.71, 3.36) and 1.35 (0.34, 0.42, 2.65, 2.83) mIU/L, respectively. Free T4 (mean (95%CI)) was 10.7 (5.9-15.5), 8.1 (4.9-11.3), 7.8 (4.5-11.0) pmol/L, respectively. In T2 and T3, 36% and 41% of the fT4 values, respectively, fell below the non-pregnancy lower normal limit. In the subgroup assessed for longitudinal changes, of the women with baseline TSH ≤ median, 71-75% remained at or below the corresponding median for trimesters 1-3. Of the women with baseline fT4 ≤ median, 69-81% also remained at or below the corresponding median for trimesters 1-3. High correlation was observed at different trimesters and baseline for TSH (Spearman's r: 0.593-0.846, P < 0.001) and for fT4 (r: 0.480-0.739, P < 0.001).Use of trimester-specific RIs would prevent misclassification of thyroid function during pregnancy. In the majority of women, TSH and fT4 tracked on the same side of the median distribution, from a non-pregnant baseline, throughout pregnancy.
Gov't Doc #: 23873872
DOI: 10.1177/0004563213486450
Journal: Annals of clinical biochemistry
Type: Journal Article
Subjects: Beckman Dxl 800 analyser
free T3
free T4
thyroid function
thyroid stimulating hormone
trimester-specific reference intervals
Longitudinal Studies
Pregnancy Trimesters.blood.physiology
Reference Standards
Thyroid Function Tests.standards
Appears in Collections:Journal articles

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