A Practical Approach for the Verification and Determination of Site- and Trimester-Specific Reference Intervals for Thyroid Function Tests in Pregnancy

Fetal sexual dimorphism of maternal thyroid function parameters during pregnancy, a single center retrospective real-world study

Introduction

Thyroid function during pregnancy fluctuates with gestational weeks, seasons and other factors. However, it is currently unknown whether there is a fetal sex-specific thyroid function in pregnant women. The purpose of this study was to investigate the fetal sex differences of maternal thyroid-stimulating hormone (TSH) and free thyroxine (FT4) in pregnant women.

Methods

This single-center retrospective real-world study was performed by reviewing the medical records of pregnant women who received regular antenatal health care and delivered liveborn infants in Shanghai First Maternity and Infant Hospital (Pudong branch), from Aug. 18, 2013 to Jul. 18, 2020. Quantile regression was used to evaluate the relationship between various variables and TSH and FT4 concentrations. The quantile regression also evaluated the sex impact of different gestational weeks on the median of TSH and FT4.

Results

A total of 69,243 pregnant women with a mean age of 30.36 years were included. 36197 (52.28%) deliveries were boys. In the three different trimesters, the median levels (interquartile range) of TSH were 1.18 (0.66, 1.82) mIU/L and 1.39 (0.85, 2.05) mIU/L, 1.70 (1.19, 2.40) mIU/L; and the median levels (interquartile range) of FT4 were 16.63 (15.16, 18.31) pmol/L, 14.09 (12.30, 16.20) pmol/L and 13.40 (11.52, 14.71) pmol/L, respectively. The maternal TSH upper limit of reference ranges was decreased more in mothers with female fetuses during gestational weeks 7 to 12, while their FT4 upper limit of the reference ranges was increased more than those with male fetuses. After model adjustment, the median TSH level was 0.11 mIU/L lower (P <0.001), and FT4 level was 0.14 pmol/L higher (P <0.001) for mothers with female fetuses than those with male fetuses during gestational weeks 9 to 12.

Discussion

We identified sexual dimorphism in maternal thyroid function parameters, especially during 9-12 weeks of pregnancy. Based on previous research, we speculated that it may be related to the higher HCG levels of mothers who were pregnant with girls during this period. However, longitudinal studies are needed to determine if fetal sex differences impact the maternal thyroid function across pregnancy.

Outcomes in Maternal Graves' Disease: A Population-Based Mother-Infant Dyad Cohort Study

Background: Graves' disease has been associated with adverse pregnancy, labor and delivery, and neonatal outcomes. Thyroid function levels, assessed during newborn screening (NBS), can serve as indicators of the adaptation in the hypothalamic-pituitary-thyroid axis. We utilized data from the national thyroid NBS program to investigate the characteristics of the mother-infant dyad of term infants born to mothers with past or active Graves' disease. Methods: The dataset of the Israeli NBS for thyroid function was linked with the electronic records of a tertiary medical center to generate a unified database of mothers and their term infants born between 2011 and 2021. The MDClone big data platform extracted maternal, pregnancy, disease course, labor and delivery, and neonatal characteristics of the mother-infant dyads. Results: Out of 103,899 registered mother-infant dyads, 292 (0.3%) mothers had past or active Graves' disease. A forward multivariate linear regression demonstrated that Graves' disease did not significantly affect NBS total thyroxine (tT4) levels (p = 0.252). NBS tT4 levels in infants born to mothers with active Graves' disease were higher than those observed in the general Israeli population (p < 0.001). Mothers with Graves' disease more frequently used assisted reproductive technology (12.7% vs. 9.0%, respectively, p = 0.012; odds ratio [OR] = 1.46 [CI 1.03-2.07], p = 0.031), and had more gestational hypertension (3.9% vs. 1.1%, p < 0.001; OR = 3.53 [CI 1.92-6.47], p < 0.001), proteinuria (2.5% vs. 0.9%, p < 0.001; OR = 3.03 [CI 1.43-6.45], p = 0.004), cesarean sections (26.4% vs. 19.7%, p = 0.029; OR = 1.46 [CI 1.13-1.90], p = 0.004), prelabor rupture of membranes (15.4% vs. 4.1%, p < 0.001; OR = 4.3 [CI 3.13-5.91], p < 0.001), and placental abnormalities (5.1% vs. 2.0%, p < 0.001; OR = 2.64 [CI 1.57-4.44]; p < 0.001). Their infants had lower adjusted birthweight z-scores (-0.18 ± 0.94 vs. -0.03 ± 0.90, p = 0.007) and were more likely to be small for gestational age (12.0% vs. 8.1%, p = 0.005; OR = 1.54 [CI 1.08-2.19], p = 0.018). Conclusions: Neonatal thyroid function levels were affected by maternal Graves' disease only when the disease was active during gestation. Moreover, maternal Graves' disease was also associated with an increased risk of adverse outcomes for the mother-infant dyad.

Partial Thyroid Hormone-Binding Globulin Deficiency: A Case Report and Literature Review

Background

Thyroxine binding globulin (TBG) deficiency is a rare thyroid disease, mostly caused by genetic mutations and acquired by X-linked recessive inheritance. The clinical features of children with TBG deficiency and their family members were summarised and the Serpina7 gene mutation was analysed, providing a reference for the differentiation of TBG deficiency.

Methods

Thyroid function was detected in TBG deficient patients, and genetic analysis was performed using polymerase chain reaction (PCR) and direct DNA sequencing to detect the characteristics of TBG mutants. Using "thyroxine binding globulin, gene and mutation" as keywords, PubMed (biomedical literature database), Web of Science and other databases were searched for relevant studies to collect and summarise relevant information.

Results

The TBG (14.7 μg/mL), 70% triiodothyronine (T3) (<0.3 nmol/L), total T3 (Tr3) (<0.05 ng/mL) and thyroxine (T4) (14.72 nmol/L) values were lower than normal, while the thyrotropin (TSH) (2.33 uIU/mL), free T3 (FT3) (1.62 pmol/L), and free T4 (FT4) (11.39 pmol/L) values were normal. These values indicate a TBG partially deficient phenotype. Using PCR amplification and direct sequencing of the target gene, a missense mutation in exon 4 of the Serpina7 gene was found in the patient and the father, and the nucleic acid variant was C.909 (exon 4) g > T; the patient was heterozygous and the father was hemizygous. The literature search retrieved a total of 45 studies, most of which were related to mutations in the Serpina7 gene. The mutation locations included exons, introns, enhancers and promoters, with exons the predominant location. A total of 49 variants of the Serpina7 gene were identified.

Conclusion

Serpina7 C.909G (P.L303F) is a mutation acquired from the father by X-linked recessive inheritance. The main clinical features of TBG deficiency patients are low serum T4, T3 and TBG levels, normal TSH, FT3 and FT4 levels, and no clinical manifestations.

Free thyroxine measurement in clinical practice: how to optimize indications, analytical procedures, and interpretation criteria while waiting for global standardization

Thyroid dysfunctions are among the most common endocrine disorders and accurate biochemical testing is needed to confirm or rule out a diagnosis. Notably, true hyperthyroidism and hypothyroidism in the setting of a normal thyroid-stimulating hormone level are highly unlikely, making the assessment of free thyroxine (FT4) inappropriate in most new cases. However, FT4 measurement is integral in both the diagnosis and management of relevant central dysfunctions (central hypothyroidism and central hyperthyroidism) as well as for monitoring therapy in hyperthyroid patients treated with anti-thyroid drugs or radioiodine. In such settings, accurate FT4 quantification is required. Global standardization will improve the comparability of the results across laboratories and allow the development of common clinical decision limits in evidence-based guidelines. The International Federation of Clinical Chemistry and Laboratory Medicine Committee for Standardization of Thyroid Function Tests has undertaken FT4 immunoassay method comparison and recalibration studies and developed a reference measurement procedure that is currently being validated. However, technical and implementation challenges, including the establishment of different clinical decision limits for distinct patient groups, still remain. Accordingly, different assays and reference values cannot be interchanged. Two-way communication between the laboratory and clinical specialists is pivotal to properly select a reliable FT4 assay, establish reference intervals, investigate discordant results, and monitor the analytical and clinical performance of the method over time.

Physiological and metabolic adaptations in pregnancy: importance of trimester-specific reference intervals to investigate maternal health and complications

Diagnosis, prognostication, and monitoring of maternal health throughout pregnancy relies on laboratory testing, including but not limited to key markers of thyroid, hepatic, cardiac, hematology, and renal function. Dynamic physiological processes during gestation significantly influence the maternal biochemistry that supports both the mother and fetus. Resultant changes in blood biochemistry alter the expected values of common laboratory tests. However, the importance of pregnancy-specific reference intervals for laboratory test result interpretation and appropriate monitoring of maternal health and complications is underappreciated. Most clinical laboratories continue to use non-pregnant adult reference intervals for laboratory test interpretation in pregnancy. The current review summarizes and critically evaluates the available literature regarding physiological and metabolic adaptations in pregnancy and their influence on common biomarkers of health and disease. The main laboratory parameters discussed include thyroid, hepatic, metabolic, renal, hematology, inflammatory, and cardiac markers. Considering the available data, further studies are urgently needed to establish trimester-specific reference intervals in healthy pregnant women on updated analytical platforms. Without such data, the standard of clinical laboratory service in pregnancy remains compromised and affects the quality of maternal-fetal healthcare.

Method-dependent variation in TSH and FT4 reference intervals in pregnancy: A systematic review

BACKGROUND

Gestational TSH and FT4 reference intervals may differ according to assay method, but the extent of variation is unclear and has not been systematically evaluated. We conducted a systematic review of published studies on TSH and FT4 reference intervals in pregnancy. Our aim was to quantify method-related differences in gestation reference intervals, across four commonly used assay methods, Abbott, Beckman, Roche and Siemens.

METHODS

We searched the literature for relevant studies, published between January 2000 and December 2020, in healthy pregnant women without thyroid antibodies or disease. For each study, we extracted trimester-specific reference intervals (2.5-97.5 percentiles) for TSH and FT4 as well as the manufacturer-provided reference interval for the corresponding non-pregnant population.

RESULTS

TSH reference intervals showed a wide range of study-to-study differences with upper limits ranging from 2.33 to 8.30 mU/L. FT4 lower limits ranged from 4.40 to 13.93 pmol/L, with consistently lower reference intervals observed with the Beckman method. Differences between non-pregnant and first trimester reference intervals were highly variable, and for most studies, the TSH upper limit in the first trimester could not be predicted or extrapolated from non-pregnant values.

CONCLUSIONS

Our study confirms significant intra- and intermethod disparities in gestational thyroid hormone reference intervals. The relationship between pregnant and non-pregnant values is inconsistent and does not support the existing practice in many laboratories of extrapolating gestation references from non-pregnant values. Laboratories should invest in deriving method-specific gestation reference intervals for their population.

First- and Second-Trimester Reference Intervals for Thyroid Function Testing in a US Population

OBJECTIVES

Thyroid dysfunction in pregnancy is associated with increased risk of adverse outcomes to mother and child. Trimester-specific reference intervals for thyroid function tests are not routinely provided by clinical laboratories. In this study, we present first- and second-trimester-specific reference intervals in a US population for thyroid-stimulating hormone (TSH), free thyroxine (FT4), total thyroxine (T4), and total triiodothyronine (T3) measured on Roche analyzers.

METHODS

We used patient samples from first- and second-trimester prenatal screening. Samples were limited to singleton pregnancies and negative screening results for thyroid peroxidase and thyroglobulin antibodies. Analytes (TSH, FT4, T4, and T3) were measured on a Roche Modular e170 then verified on a Roche cobas e801.

RESULTS

The reference intervals established on the e170 and verified on the e801 for the first trimester were 0.16 to 2.82 mIU/L for TSH, 12.0 to 18.5 pmol/L for FT4, 62.8 to 177.9 nmol/L for T4, and 1.5 to 3.4 nmol/L for T3. The reference intervals for the second trimester were 0.40 to 3.62 mIU/L for TSH, 10.2 to 16.6 pmol/L for FT4, 66.6 to 176.0 nmol/L for T4, and 1.56 to 3.6 nmol/L for T3.

CONCLUSIONS

This is the first report of trimester-specific reference intervals for thyroid function tests on Roche analyzers in the United States, and it is consistent with worldwide reports.

Evaluation of median urinary iodine concentration cut-off for defining iodine deficiency in pregnant women after a long term USI in China

BACKGROUND

The WHO/UNICEF/ICCIDD define iodine deficiency during pregnancy as median urinary iodine concentration (MUIC) ≤ 150 μg/L. China implemented universal salt iodization (USI) in 1995, and recent surveillance showed nationwide elimination of iodine deficiency disorders (IDD). Data from 2014 showed that the MUIC in 19,500 pregnant women was 154.6 μg/L and 145 μg/L in 9000 pregnant women in 2015. However, symptoms of iodine deficiency were absent. Our study sought to evaluate whether MUIC below 150 μg/L affects thyroid function of Chinese pregnant women and their newborns in Chinese context.

METHODS

We screened 103 women with normal thyroid function and MUIC lower than 150 μg/L during week 6 of pregnancy at Peking Union Medical College Hospital. Patient demographics and dietary salt intake were recorded. Subjects were followed at 12, 24, and 32 gestational weeks. At each visit, a 3-day dietary record, drinking water samples, and edible salt samples were collected and analyzed for total dietary iodine intake. Additionally, 24-h urine iodine and creatinine were measured. Blood tests assessed thyroid function in both mothers and newborns.

RESULTS

Of 103 pregnant women enrolled, 79 completed all follow-up visits. Most subjects maintained normal thyroid function throughout pregnancy. However, 19 had thyroid dysfunction based on thyroid stimulating hormone and free thyroxine levels. The median serum iodine was 71 μg/L (95% CI: 44, 109). The median thyroglobulin was < 13 μg/L. values above this level indicate iodine deficiency in pregnant women. The median dietary iodine intake during pregnancy, derived from the 3-day record and measures of water and salt, was 231.17 μg/d. Assuming 90% urinary iodine excretion (UIE), 200.11 μg/d UIE means the 222.34 μg iodine loss per day, suggesting that subjects had a positive iodine balance throughout pregnancy. All neonatal blood samples showed TSH levels lower than 10 mIU/L, indicating normal thyroid function. No significant difference was found among gestational weeks for urinary iodine, and the MUIC in subjects who completed 3 follow-up visits was 107.41 μg/L.

CONCLUSION

Twenty years after implementing USI, expectant Chinese mothers with MUIC of 107.4 μg/L, less than the WHO's 150 μg/L benchmark, maintained thyroid function in both themselves and their newborn babies.