Trimester specific reference intervals for thyroid function tests in normal Indian pregnant women

Effects of treating subclinical hypothyroidism in pregnancy in India: Are we treating too many for little gain? A retrospective cohort study

OBJECTIVE

To assess the impact of treatment of subclinical hypothyroidism (SCH) on short-term pregnancy outcomes.

METHOD

Data from 4526 consecutive women with singleton pregnancies who delivered between January 2015 and December 2017 were analyzed. SCH was defined as a thyroid-stimulating hormone (TSH) level between 2.5 and 10 mU/mL with normal free thyroxine. Of those with SCH, some were treated but others were not. These two groups were compared using χ2 and Student t tests for categorical and continuous variables, respectively. Multiple logistic regression models, adjusted for maternal age, body mass index, parity, gestation at TSH measurement, and gestational diabetes mellitus status, were used to investigate the effect of treatment on pregnancy and neonatal outcomes.

RESULTS

In all, 1227 (27.1%) of 4526 women had SCH, of whom 393 (32.0%) were treated. The mean age and body mass index were similar in both groups. The mean gestation at measuring of TSH was 11.7 ± 6.5 weeks. There was no significant difference in pregnancy or neonatal outcomes between the two groups. A sub-group analysis when SCH was defined as TSH 4.0 mU/mL or greater showed a higher rate of large for gestational age and lower rates of low birth weight and small for gestational age in the treated group.

CONCLUSIONS

The prevalence of SCH based on the international guidelines threshold is high in India. Treatment of SCH did not show any difference in pregnancy and neonatal outcomes in this study.

Trimester-specific reference intervals for thyroid function parameters in pregnant Caucasian women using Roche platforms: a prospective study

BACKGROUND

Standard thyroid function parameters reference intervals (RI) are unsuitable during pregnancy, potentially resulting in incongruous treatments that may cause adverse effects on pregnancy outcomes. We aimed at defining trimester-specific TSH, FT4 and FT3 RI, using samples longitudinally collected from healthy Caucasian women.

MATERIALS AND METHODS

Blood samples from 150 healthy Caucasian women, who had a physiological gestation and a healthy newborn at term, were collected in each trimester and at around six months post-partum. They showed mild iodine deficiency. After excluding women with overt TSH abnormalities (> 10 mU/L) and/or TPO antibodies, data from 139 pregnant women were analyzed by means of widely used Roche platforms, and TSH, FT4 and FT3 trimester-specific RI were calculated. Post-partum data were available for 55 subjects.

RESULTS

Serum TSH RI were 0.34-3.81 mU/L in the first trimester, and changed slightly to 0.68-4.07 U/L and 0.63-4.00 mU/L in the second and third trimester, respectively. Conversely, both FT4 and FT3 concentrations progressively decreased during pregnancy, the median values in the third trimester being 14.8% and 13.2% lower, respectively, than in the first trimester. Thyroid function parameters in the first trimester were similar to those measured after the end of pregnancy.

CONCLUSIONS

This study calculates trimester-specific RI for thyroid function parameters in pregnancy, and proposes the reference limits that should be adopted when using Roche platforms in Caucasian women.

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.

Iodine Status in Pregnant Women Having Urinary Fluoride in Contaminated Areas: A Case Study of Phayao Province

Fluoride naturally occurs in the Earth's crust and is widely dispersed in groundwater. The high consumption of fluoride can inhibit iodine metabolism in the human body, especially in the thyroid gland. This study assessed iodine knowledge, iodine consumption behavior, urinary iodine (UI), thyroid stimulating hormone (serum TSH), and free triiodothyronine3 (serum FT3) and examined the connection between fluoride exposure and UI and thyroid function as serum concentrations of TSH and FT3 in pregnant women dwelling in an area of endemic fluorosis. This was a cross-sectional study. The population included 152 pregnant women within the 1^st trimester of pregnancy, during which they were provided antenatal care (ANC) in seven public community hospitals in Phayao province, Thailand. The study consisted of two components. First, the study consisted of a questionnaire in which we evaluated the iodine knowledge and iodine consumptive behaviors in subjects. Second, biochemical data were investigated to evaluate thyroid function in the subjects. The gestational age of most subjects was 8-12 weeks. The study population has lived in fluoride-contaminated areas since birth (76.97%). The iodine and iodine consumption levels were moderate (50.00%). Their food iodine consumption was 3-4 days/week, and the top five consumption ranks were iodized salt, cooked pork, eggs, sticky rice, and iodine fish sauce. In terms of biochemical parameters, 63.16% of respondents had UI levels below 150.00 g/L, which is below the normal reference range of 150.00-249.00 g/L. 89.47% of the risk of hypothyroidism was associated with serum TSH levels below 2.50 g/L. In 38.16% of the samples, normal levels of serum FT3 (2.00-4.40 pg/L) were identified in the subjects. In addition, 61.84% of the samples had FT3 concentrations greater than 4.40 pg/L (high intake of iodine). The approved association between positive serum FT3 data and serum TSH was positive (r = 260 and p < 0.05). These studies imply that these elevated levels of TSH and FT3 place pregnant women in their first trimester at risk for hypothyroidism.

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.

Trimester-specific reference intervals of thyroid function tests in Turkish pregnants

Physiological changes in hormone levels occur in thyroid gland during pregnancy. Screening of the thyroid hormone levels and determining trimester-specific reference intervals in pregnancy are important. Guidelines recommend the use of trimester-specific reference ranges for each country. The aim of this study is to determine trimester-specific thyroid function reference intervals for pregnancy in Turkish population. In total, 5000 patients were screened out of which 1258 patients have all of fT3, fT4 and TSH levels measured, were included in the study. Patients were grouped as follows: 482 women were in first trimester, 361 women were in second trimester, and 415 women were in third trimester. All analyses were performed by means of chemiluminescence methods (Liaison^®; DiaSorin S.p.A., Saluggia, Italy). The TSH reference intervals were 0.005-3.65, 0.01-3.63, and 0.2-3.46 mIU/L at the first, the second, and the third trimesters of pregnancy, respectively. The fT4 reference intervals were 0.72-1.79, 0.71-1.26, and 0.65-1.12 ng/dL at the first, the second, and the third trimesters, respectively. The fT3 reference intervals were 2.45-4.03, 2.37-3.85, and 2.31-3.77 ng/dL at the first, the second, and the third trimesters, respectively. It is crucial to determine population- and gestational-specific reference intervals for trustworthy treatment of pregnants.

Trimester-Specific Reference Intervals for Thyroid Function Parameters in Indian Pregnant Women during Final Phase of Transition to Iodine Sufficiency

BACKGROUND

Interpretation of thyroid function tests during pregnancy depends on gestational age, method, and population-specific reference intervals. Therefore, there is a worldwide trend to establish trimester-specific levels for different populations. The aim of this study was to establish a trimester-specific reference range for thyroid function parameters during pregnancy in Indian women.

MATERIALS AND METHODS

Thyroid function tests (TSH, FT4, TT4, TT3) of 80, 76, and 73 women at 1^st, 2^nd, and 3^rd trimester, respectively, and 168 nonpregnant women were analyzed after exclusion of low UIC(<150 μg/L) and anti-TPO positivity(>35 IU/ml). Urinary iodine excretion (UIC) was assessed in all. The 2.5^th and 97.5^th percentile values were used to determine the reference ranges for thyrotropin (TSH), free thyroxine (FT4), total thyroxine (TT4), and total triiodothyronine (TT3) for each trimester of pregnancy.

RESULTS

The reference range for TSH for first trimester was 0.19-4.34 μIU/ml, for second trimester 0.46-4.57 μIU/ml, and for third trimester 0.61-4.62 μIU/ml. The reference range during three trimesters for FT4 (ng/dl) was 0.88-1.32, 0.89-1.60, and 0.87-1.54, for total T4 (μg/dl) was 5.9-12.9, 7.4-15.2, and 7.9-14.9. In nonpregnant women, FT4 was 0.83-1.34, total T4 was 5.3-11.8, and TSH was 0.79-4.29. The mean UIC in nonpregnant women was 176 ± 15.7 μg/L suggesting iodine-sufficiency in the cohort.

CONCLUSION

The trimester-specific TSH range in pregnant women in this study is not significantly different from nonpregnant reference range in the final phase of transition to iodine sufficiency in India.

Thyroid-stimulating hormone (TSH) serum levels and risk of spontaneous abortion: A prospective population-based cohort study

OBJECTIVE

Thyroid dysfunction, a common complication of pregnancy, is associated with adverse obstetric and neonatal consequences. This study aimed to determine the effect of TSH levels on early pregnancy outcome in a prospective population-based cohort study.

DESIGN AND METHODS

The serum TSH, free thyroxine, free triiodothyronine, thyroid peroxidase antibody levels and urinary iodine concentration of 418 pregnant women in their first trimester of pregnancy were measured. According to the American Thyroid Association (ATA) and the local reference ranges for TSH, women were divided into two groups of 0.1-2.5, >2.5 mIU/L and 0.2-4.6, >4.6 mIU/L. The risk of spontaneous abortion (SA) was calculated for each group.

RESULTS

Spontaneous abortion was detected in 7.2% (n = 30) of total 418 pregnancies. Women with TSH levels > 2.5 mIU/L had an increased risk of SA, compared to women with TSH levels of 0.1-2.5 mIU/L (relative risk [RR] 3.719, 95% confidence interval [CI]:1.713-8.074). The risk of SA was increased in women with TSH levels > 4.6 mIU/L (RR 5.939, 95% CI: 1.711-20.620). The rate of SA was increased by 78% for every unit increase in standard deviation of TSH concentration (RR 1.35, 95% CI: 1.09-1.70). The rate of miscarriages in the treated group by levothyroxine was 9.8% (n = 6) compared to 28.6% (n = 8) in the untreated group (P = 0.024).

CONCLUSIONS

Our finding suggests that the upper limit for the TSH normal range should be redefined to <2.5 mIU/L during the first trimester of gestation. The local upper limit was 4.6 mIU/L, consistent with 4.0 mIU/L cut-off value recommended by the ATA.

Reference Intervals for Thyroid Hormones During the First Trimester of Gestation: A Report from an Area with a Sufficient Iodine Level

The physiological changes during pregnancy modulate the endocrine system. Therefore, both the American and the European thyroid associations recommend the use of local trimester-specific reference intervals. The purpose of this study was to establish the first trimester reference intervals for thyroid function tests in the central area of Iran. We examined 436 pregnant women in their first trimester of pregnancy, and 444 non-pregnant women in a cross sectional study. Serum levels of thyroid stimulating hormone (TSH), free thyroxin (FT₄), free triiodothyronine (FT₃), thyroid peroxidase antibody, urinary iodine concentration (UIC), and thyroid volume were measured for all subjects. The first trimester-specific reference intervals (2.5th-97.5th percentile) were determined for 185 pregnant women and 256 non-pregnant women with negative TPOAb, adequate iodine level (UIC≥150 μg/l in pregnant and UIC≥100 μg/l in non-pregnant women), and normal thyroid examination. We calculated multiples of the median (MoM) for TFTs to normalize the obtained data. The first trimester-specific reference intervals of serum TSH, FT₄, and FT₃ for pregnant women were 0.20-4.60 mIU/l, 9.0-18.02 pmol/l, and 3.40-5.64 pmol/l, respectively, while the corresponding figures for non-pregnant women were 0.59-5.60 mIU/l, 9.52-19.30 pmol/l, and 3.70-5.55 pmol/l, respectively. The first and 99th percentile MoM of TSH in pregnant women in their first-trimester was 0.06-4.62. The local normal reference ranges for the first trimester of pregnancy in central region of Iran were different from the ranges suggested by the ATA.

A Systematic Review on Normative Values of Trimester-specific Thyroid Function Tests in Indian Women

BACKGROUND

Small cross-sectional studies are published on the trimester-specific normal ranges of thyrotropin and thyroxine levels in Indian women from various parts of the country.

OBJECTIVE

We sought to review the published literature on thyroid function tests in normal pregnant Indian women to see if the pooled data from various studies can define normative data and hypothyroidism in pregnancy.

METHODS

We retrieved 56 studies from online databases with detailed search using multiple search terms. Unanimously eight studies were finalized.

RESULTS

Data of 2703 pregnant women (age 16-45 years; 966 were in the first trimester, 1072 in their second trimester, and 1037 women in their third trimester) were analyzed. All eight studies included singleton pregnancies from the northern and eastern part of India with seven studies being cross-sectional in nature. The exclusion criteria in all studies included those with historical/clinical evidence of thyroid dysfunction, those with family history of thyroid dysfunction, infertility and those with history of recurrent miscarriages (usually >3). Ultrasound evidence of thyroid disease, urinary iodine assessment, and thyroid antibodies were included as additional exclusion criteria in two, three, and four studies, respectively. None of the studies included the outcome of pregnancy as part of follow-up. As part of the pooled data analysis, the 5^th-95^th centile values of normal TSH extended from 0.09 to 6.65 IU/mL in the first trimester, 0.39-6.61 IU/mL in the second trimester, and 0.70-5.18 IU/mL in the third trimester. The FT4 levels (5^th-95^th centile values) extended from 8.24 to 25.74 pmol/L in the first trimester, 6.82-26.0 pmol/L, and 5.18-25.61 pmol/L in the third trimester.

CONCLUSIONS

With due limitations imposed by the quality of the available studies, the current review suggests that upper normal limit of TSH values can extend up to 5-6 IU/mL in pregnancy.