Changes of Thyroid Function Tests in Pregnancy and Contribution of Trimester Specific Reference Ranges to Diagnosis

Abstract

A AB BS ST TR RA AC CT T O Ob bj je ec ct ti iv ve e: : Non pregnant reference ranges are not appropriate in pregnancy because of the pregnancy associated changes in thyroid physiology. The aim of the study is to determine thyroid hormone status in trimesters of pregnancy and to show the clinical significance of using pregnancy associated values in thyroid stimulating hormone (TSH), free triiodothyronine (fT3) and free thyroxine (fT4) tests. M Ma at te er ri ia al l a an nd d M Me et th ho od ds s: : 319 pregnant women followed by the gynaecology and obstetrics clinic of our hospital were prospectively included. All tests were measured by Abbott Architect i400SR analyzer with chemiluminescent microparticle immunoassay (CMIA) method. The results were given as median and 2.5-97.5 percentiles. R Re es su ul lt ts s: : The study population was composed of 319 women with a mean±SD age of 26.8±4.8 years; 96 pregnant were in the 1 st trimester (9-13 weeks), 84 in the 2 nd trimester (16-20 weeks) and 139 in the 3 rd trimester (24-28 weeks). Median (2.5-97.5 percentile) values for TSH were found as 1.062 (0.035-2.955), 1.527 (0.334-2.70) and 1.740 (0.540-4.420) mIU/L for the 1 st , 2 nd and 3 rd trimesters respectively. When using non-pregnant cut-off values, subclinic hypothyroid patients would be misdiagnosed; 2/96 (2.08%), 2/84 (2.38%) and 4/139 (2.87%) in the 1 st , 2 nd and 3 rd trimesters respectively. Pregnant values found in this study were also different from the American Thyroid Association (ATA) recommended cut-off's. Use of ATA cut-off's, (4/96) 4.16% in the 1 st ; (2/84); 2.38% in the 2 nd and (12/139) 8.6% in the 3 rd trimester would be misdiagnosed. C Co on nc cl lu us si io on n: : We can conclude that thyroid function test levels can change during pregnancy and laboratory specific reference ranges should be established to avoid misinterpretation for all trimesters.K Ke ey y W Wo or rd ds s: : Reference values; pregnancy; thyroid function tests Ö ÖZ ZE ET T A Am ma aç ç: : Tiroid fizyolojisindeki gebeliğe bağlı değişimlerden dolayı, gebelerde gebelik dışı referans aralıklarının kullanımı uygun değildir. Bu çalışmanın amacı, farklı gebelik trimesterlerinde tiroid hormon durumunu belirlemek ve tiroid stimulan hormon (TSH), serbest triiyodotironin (sT3) ve serbest tiroksin (sT4) testlerinde gebelik ilişkili referans aralığı kullanmanın tanısal önemini belirlemektir. G Ge er re eç ç v ve e Y Yö ön nt te em ml le er r: : Hastanemizin jinekoloji ve obstetrik kliniğinde izlenen 319 gebe kadın çalışmaya dâhil edildi. Tüm testler Abbott Architect i400SR cihazında, kemiluminesan mikropartikül immunoassay (CMIA) metodu ile çalışıldı. Sonuçlar median ve 2,5-97,5 persentil olarak verildi. B Bu ul lg gu ul la ar r: : Çalışma populasyonu yaş ortalama±SS'si 26,8±4,8 yıl olan; 96'sı 1. trimester (9-13 haftalık), 84'ü 2. trimester (16-20 haftalık), 139'u 3. trimester (24-28 haftalık) 319 kadından oluşmaktadır. TSH için median (2,5-97,5 persentil) değerleri 1, 2 ve 3. trimesterler için sırasıyla 1,062 (0,035-2,955), 1.527 (...