Establishment of assay method‐ and trimester‐specific reference intervals for thyroid hormones during pregnancy in Chengdu, China

Abstract

Background The reference intervals of thyroid hormone will change at different stages of pregnancy because of physiological alterations. On the other hand, the reference intervals of thyroid hormone will also change in different detection systems due to the manufacturer's methodology as well as a different race. The objective of this study was to establish the assay method‐ and trimester‐specific reference intervals for thyroid‐stimulating hormone, free thyroxine and free triiodothyronine for pregnant women in Chengdu. Methods A prospective, population‐based cohort study involved 23,701 reference samples of pregnant women during the three trimesters and 8646 non‐pregnant women with pre‐pregnancy clinical and laboratory tests. The 2.5th and 97.5th percentiles were calculated as the reference intervals for thyroid‐stimulating hormone, free thyroxine and free triiodothyronine at each trimester of pregnant women according to ATA Guidelines. Results The reference interval of thyroid‐stimulating hormone in the 2.5th and 97.5th percentiles has a significant increasing trend from the first trimester, to second trimester and to third trimester, which was 0.08–3.79 mIU/L for the first trimester, and 0.12–3.95 mIU/L for the second trimester and 0.38–4.18 mIU/L for the third trimester, respectively (p < 0.001). However, the reference intervals of free thyroxine and free triiodothyronine in the 2.5th and 97.5th percentiles have significant decreasing trends from the first trimester, to second trimester and to third trimester, which were 11.87–18.83 pmol/L and 3.77–5.50 pmol/L for the first trimester, and 11.22–18.19 pmol/L and 3.60–5.41 pmol/L for the second trimester, and 10.19–17.42 pmol/L and 3.37–4.79 pmol/L for the third trimester, respectively (both p < 0.001). Conclusion It is necessary to establish assay method‐ and trimester‐specific reference intervals for thyroid‐stimulating hormone, free thyroxine, and free triiodothyronine because the reference intervals of these thyroid hormones are significantly different at different stages of pregnancy.

Laboratory policies and practices for thyroid function tests in Croatia: survey on behalf of Working Group for Laboratory Endocrinology of the Croatian Society of Medical Biochemistry and Laboratory Medicine

“…Additionally, during pregnancy reference interval should be listed according gestation weeks. Unfortunately, most manufacturers do not provide reference intervals for children and pregnant women and many studies are done in order to fill this gap (31)(32)(33). All these issues complicate the interpretation and comparability of laboratory results for TSH and there is an urgent need for standardization of thyroid hormone assays to reduce inter-laboratory variation.…”

Association between third trimester maternal isolated hypothyroxinemia and adverse pregnancy outcomes

“…different reference ranges for the serum TSH and FT4 levels [26][27][28]. In addition, the ethnicity, iodine deficiency status, and the gestational weeks when blood is collected can all influence the serum TSH and FT4 test results [29,30].…”

Maternal thyroid peroxidase antibody positivity and its association with incidence of low birth weight in infants

“…The recorded adverse pregnancy outcomes were as follows: LBW, premature rupture of membranes, premature birth, fetal distress, and low Apgar score in newborns at 1 minute after birth. Infants with LBW were defined as birth weight < 2500 g (14); premature rupture of membranes was defined as rupture of the amniotic sac and chorionic villi before labor (15); preterm birth was defined as delivery < 37 weeks of gestation; fetal distress was defined as fetal heart rate < 120 beats/min or > 160 beats/min, with meconium, fetal movement abnormalities, and fetal scalp pH < 7.2 ( 16); Apgar score < 7 was considered as low (17).…”