Comparison of thyroid function in pregnant and non-pregnant Asian and western Caucasian women

The origin of ferritin reference intervals: a systematic review

Iron deficiency is a highly prevalent condition, which contributes to unnecessary morbidity, mortality, and health inequity. A serum ferritin concentration of less than 30 μg/L has a high specificity and sensitivity for diagnosing iron deficiency in adults, but the laboratory reported lower limit of normal (LLN) is typically lower. These LLNs might not be rooted in rigorous scientific evidence and might be contributing to structural underdiagnosis of iron deficiency. A systematic review was done per systematic reviews and meta-analysis guidelines with the use of medical literature databases from inception of each database to Nov 30, 2021, to identify studies that determined ferritin reference intervals in healthy adults and grey literature search for the five most common ferritin assays (registration number CRD42022268844). The objectives were to systematically summarise the ferritin reference intervals and to do a methodological quality assessment of the included studies. 2306 studies were screened and 61 full texts were included. 37 studies were eligible for analysis of the ferritin LLN in the general population. The population the sample was comprised of was a total of 21 882 females and 23 650 males participants. The ferritin LLN was a median of 8 μg/L (IQR 5-15) and mean of 9 μg/L (SD 11) in females and a median of 25 μg/L (IQR 16-44) and mean of 25 μg/L (SD 29) in males. 30 (49%) of 61 studies did not explicitly screen for patients at risk of iron deficiency, and 32 (52%) did not refer to a reference interval establishment guideline (eg, guideline recommended by Clinical and Laboratory Standards Institute). The five most used commercial ferritin laboratory assays reported reference intervals with a median LLN of 11 (IQR 9-12) and mean of 9 μg/L (SD 4) for females and median of 22 (IQR 22-24) and mean of 23 μg/L (SD 4) for males. In the literature, serum ferritin reference intervals in healthy adults consistently report a LLN of less than 30 μg/L. Data driving these ferritin reference intervals are at high risk of bias, given no exclusion of individuals at risk for iron deficiency in the presumed normal population sample and no adherence to reference interval establishment standards. We suggest the use of evidence-based laboratory clinical decision limits to diagnose iron deficiency.

Risk factors for hypothyroidism following hemithyroidectomy

OBJECTIVE

Hypothyroidism is the most common complication of hemithyroidectomy for thyroid nodules. This retrospective cohort study investigated the prognostic factors for hypothyroidism following hemithyroidectomy.

METHODS

We included patients who underwent hemithyroidectomy between 2016 and 2017, excluding those with history of preoperative hypothyroidism or malignancy on histopathological examination. The primary endpoint was development of hypothyroidism during follow-up (TSH≥2 above normal).

RESULTS

Twenty-six of the 128 included patients (20%) developed postoperative hypothyroidism. The following independent prognostic factors were found: preoperative TSH level>1.5 mIU/L (OR 2.11; P=0.013), and remaining thyroid volume adjusted for body surface area<4.0mL/m2 (OR 1.77; P=0.015). Twenty-one patients (81%) had first TSH values above the upper limit of normal. Postoperatively, first TSH level correlated significantly with the preoperative value (R=0.5779, P<0.001). Levothyroxine was prescribed to 16% of patients, with a mean dose of 0.92μg/kg/day.

CONCLUSION

Patients with TSH>1.5 mIU/or remaining thyroid volume adjusted for body surface area<4.0mL/m2 should have intensified clinical and biological follow-up in the first year after surgery.

Trimester-specific reference ranges for thyroid hormones of pregnant females at tertiary care hospitals in Lahore, Pakistan

BACKGROUND

The significance of investigation for diagnosing and managing thyroid dysfunction in pregnant females has been extensively documented in the medical literature. This study aimed to determine trimester-specific reference ranges for thyroid-stimulating hormones (TSH), free T3 (FT3), and free T4 (FT4) in apparently healthy pregnant women attending tertiary care hospitals in Lahore.

METHODS

This cross-sectional study was conducted at two tertiary care Hospitals in Lahore, Pakistan. In this multi-centric study, 500 pregnant females were initially enrolled from September 2019 to December 2019 who fulfilled the inclusion criteria. For measurement of serum FT3, FT4, thyroid stimulating hormone (TSH), anti-thyroid peroxidase (anti-TPO), and thyroglobulin antibodies, 5 ml of the blood sample was drawn, under aseptic conditions, from each subject using Maglumi 800 chemiluminescence immunoassay (CLIA) system.

RESULTS

Out of 500 subjects, 23 subjects with positive anti-TPO, 19 subjects with anti-TG antibodies, and 12 subjects due to less volume of serum yielded from whole blood (serum less than 3 ml) were excluded from the analysis. Ten samples were hemolyzed and not included in the analysis. A total of 436 samples were examined for analysis. Of the remaining 436 subjects, 133 (30.5%) were from 1st trimester, 153 (35.1%) from 2nd trimester, and 150 (34.4%) from 3rd trimester. As the data were non-normal, the 2.5th, 50th, and 97.5th percentiles were calculated to express each group's results. Trimester specific range of TSH 0.168-4.294, 0.258-4.584 and 0.341-4.625 mIU/mL, FT31.857-4.408, 1.958-4.621 and 2.025-4.821 pmol/L and FT4 8.815-18.006, 8.306-17.341 and 7.402-17.292 pmol/L.

CONCLUSION

In this study, we established a trimester-specific reference range for our local population's thyroid function test. The results of this study have complemented the results of previous studies.

Thyroid Function During Pregnancy in A Multiethnic Population in Norway

Context

Ethnic differences in thyroid function during pregnancy have been reported. However, it is unclear if this is equally valid across ethnic groups within multiethnic populations.

Objective

We aimed to assess ethnic differences in thyrotropin (TSH) and free thyroxine (FT4), and the prevalence of thyroid dysfunction and thyroid autoimmunity during pregnancy.

Methods

In a population-based cohort of 785 pregnant women in Oslo, Norway, TSH, FT4, and thyroid peroxidase antibodies (TPO Abs) were measured twice: at gestational week (GW) 15 and 28, and urine iodine concentration at GW 15. Associations were assessed using multivariate linear regression.

Results

We found ethnic differences in TSH levels at both time points, but not for fT4. South Asians had 0.42 mU/L (95% CI, 0.20-0.64) higher TSH than Europeans in GW 15. This difference persisted after adjusting for covariates (including TPO Ab positivity and iodine status), and increased further as pregnancy progressed. In contrast, East Asians had the lowest TSH. No new cases of overt hypothyroidism were detected in early pregnancy, but subclinical hypothyroidism was found in 6.6% among all, highest in South Asians (14.2%). Hyperthyroidism early in pregnancy was observed in 3.7% (almost all subclinical), highest in East Asians (11.9%). The prevalence of TPO Ab positivity was 4%, highest in South Asians (8%).

Conclusion

In a multiethnic population of presumably healthy women, we found ethnic variations in TSH but not FT4 levels throughout pregnancy. South Asians had higher TSH and more subclinical hypothyroidism, not explained by their higher prevalence of TPO Ab positivity. Larger studies are needed to define ethnic- and trimester-specific reference ranges in pregnancy.

Prevalence of Thyroid Disorder in Pregnant Women Visiting a Tertiary Care Teaching Hospital: A Descriptive Cross-sectional Study

Introduction:

The function of the thyroid gland is altered during pregnancy. Thyroid disorders during pregnancy are associated with serious maternal and fetal outcomes. Universal screening for thyroid disorders is recommended in the first trimester of pregnancy. This study aims to determine the prevalence of thyroid disorder during pregnancy in women attending a tertiary care hospital.

Methods:

A descriptive cross-sectional study was conducted in the Department of Obstetrics and Gynaecology of Kathmandu Medical College and Teaching Hospital from March 2020 to August 2020 after obtaining ethical approval from the Institutional Review committee with reference number 20032020. The pregnant women >18 years of age, irrespective of their gestational age and gravida status, were included in the study by convenience sampling method. The participants were screened by estimation of thyroid function test. Data were collected, and statistical analysis was done in Statistical Packages for Social Services version 20.0.

Results:

A total of 329 pregnant women were included in this study. The prevalence of thyroid disorders in the present study is 24.62%. The most common thyroid disorder observed was subclinical hypothyroidism comprising 65 (19.75%) cases followed by overt hypothyroidism 8 (2.43%) cases.

Conclusions:

There is a high prevalence of thyroid disorders during pregnancy in our settings. Timely screening of pregnant women helps in the early diagnosis and management of complications related to thyroid disorders.

Pitfalls in the assessment of gestational transient thyrotoxicosis

Gestational transient thyrotoxicosis (GTT) is associated with direct stimulation of the maternal thyroid gland by human chorionic gonadotropin (hCG). It is characterized by slightly higher thyroid hormone and lower thyroid-stimulating hormone (TSH) levels in early pregnancy and mild or no symptoms. While GTT must be distinguished from Graves' disease (GD), which is associated with maternal and fetal complications, treated GD and new-onset GD in pregnancy are occasionally challenging to distinguish. Evaluating serum hCG levels and TSH receptor antibody (TRAb) titers can help, but the results are not irrefutable due to pregnancy-related immunosuppression. Moreover, GTT can follow unusual clinical courses in relation to some pregnancy complications. Excessive hCG production can cause severe GTT symptoms in patients with hyperemesis gravidarum, trophoblastic disease, or multiple pregnancies. Thyrotoxicosis can emerge beyond the second trimester in patients with gestational diabetes mellitus and mirror syndrome, because of delayed elevations in the hCG levels. Detailed knowledge about GTT is necessary for correct diagnoses and its appropriate management. This review focuses on the diagnosis of GTT, and, particularly, its differentiation from GD, and unusual clinical conditions associated with GTT that require comprehensive management.

Gestational TSH and FT4 Reference Intervals in Chinese Women: A Systematic Review and Meta-Analysis

Background: Serum thyroid-stimulating hormone (TSH) and free thyroxine (FT4) change dynamically during pregnancy. Differences in geographic regions, populations, and manufacturer's methodologies can affect the reference intervals for thyroid function tests. The 2017 guidelines of the American Thyroid Association (ATA) recommended 4.0 mU/L as the cut-off point for the upper limit of serum TSH in early pregnancy. A systematic review is called for to establish practical, gestational-specific TSH and FT4 reference intervals for pregnant Chinese women and to explore whether the criteria are suitable for China. Methods: English and Chinese articles published from inception to Aug 2017 were searched in the PubMed, EMBASE, and SCIE English-language databases and the CNKI, WanFang, and CQVIP Chinese databases. The relative descent or ascent rates of serum TSH and FT4 were calculated, after which Comprehensive Meta-Analysis V2.0 software was used to analyze the data. Results: Eleven studies (6 in English and 5 in Chinese), five kits and 11,629 Chinese women from nine cities were considered in this meta-analysis. Compared with the reference ranges provided by manufacturers, serum TSH decreased in the first trimester, with the upper limit declining by 21.7% (5.0-36.6%), to a value close to 4.0 mU/L, and the lower limit declining by 85.7% (73.5-97.1%). It continued decreasing in the second trimester, with the upper limit declining by 24.0% (6.4-40.9%) and the lower limit declining by 40.7% (9.0-85.7%). For FT4, the upper limit fluctuated slightly, and the lower limit increased by 6.8% (1.0-14.6%) in the first trimester. Serum FT4 dropped gradually, with the upper limit declining by 21.8% (2.5-31.8%) and the lower limit declining by 12.7% (2.6-19.6%) in the second trimester. During the third trimester, the upper limit decreased by 25.1% (12.7-35.0%), while the lower limit decreased by 20.9% (14.8-27.3%). Conclusions: Various regions, kits and test methods affect the gestational TSH and FT4 levels. The non-pregnant serum TSH upper limit minus 22% is very close to 4.0 mU/L, which can be used as a sub-optimal approach to represent the cut-off value for pregnant Chinese women in the first trimester.

Trimester-specific reference interval for thyroid hormones during pregnancy at a Tertiary Care Hospital in Haryana, India

BACKGROUND

Reference intervals for thyroid hormone during pregnancy need to be gestational age, method, and population specific and there is need to establish trimester-specific thyroid levels for the different population across the world. The aim of this study was to establish trimester-specific reference range for thyroid hormone during pregnancy in a tertiary care center in Haryana.

MATERIALS AND METHODS

A total of 1430 pregnant women were recruited for the study. Participants having any history of chronic illness, goiter on physical examination, thyroid illness in the past or present, consuming thyroid medications, family history of thyroid illness, presence of anti-thyroid peroxidase antibody, poor obstetrics history were excluded from the study and reference population was identified to calculate serum free triiodothyronine (FT3), free thyroxine (FT4) and thyrotropin (TSH) for each trimester of pregnancy.

RESULTS

The 2.5-97.5th percentiles for FT3, FT4, and TSH obtained in this study were 2.53-4.54 pg/ml, 0.88-1.78 ng/ml and 0.37-3.69 μIU/ml in the first trimester, 2.0-4.73 pg/ml, 0.91-1.78 ng/ml and 0.54-4.47 μIU/ml in the second trimester, 2.01-4.01 pg/ml, 0.83-1.73 ng/ml, and 0.70-4.64 μIU/ml in the third trimester of pregnancy. Mean TSH increased and mean FT3 decreased significantly with the progression of gestational period. FT4 decreased from trimester 1-3rd, but the decrease was nonsignificant from 2nd to 3rd trimester.

CONCLUSIONS

Existing results for trimester-specific reference intervals for thyroid hormones are inconsistent and cannot be extrapolated due to differences in ethnicity, maternal iodine status, laboratory assay method, and rigor for selection of reference population. Thus, establishment of reference intervals in each region is of great importance.

Reference intervals in evaluation of maternal thyroid function of Manipuri women

CONTEXT

The population of Manipur is of different ethnic background from the rest of the country. Several authors have suggested population/ethnic and laboratory specific reference range of maternal thyroid profile of different trimesters.

AIMS

To find the reference range of thyroid stimulating hormone (TSH), total thyroxine (TT4) and total tri-iodothyronine (TT3) levels for normal pregnant women of native Manipur descendants.

SETTINGS AND DESIGN

The cross-sectional study was conducted at a teaching Institute after ethical clearance was obtained.

SUBJECTS AND METHODS

A reference populations of 375 normal pregnant women were established after screening about 600 pregnant women. The study excluded patients with hyperemesis gravid arum, past history or family history of thyroid disorders as well as the connective tissue disorders, WHO grade 1 or 2 goiter, or any medications that alter thyroid functions. The serum levels of TSH, TT4, and TT3 were measured using chemiluminescence assay.

STATISTICAL ANALYSIS USED

Data for TT3 and TT4 were expressed as mean ± standard deviation, median and 5-95(th) percentiles.

RESULTS

The mean TSH in the three trimesters was 1.06 + 0.45, 1.23 + 0.30, and 1.25 + 0.36, respectively. The normal reference range thus was different from that of the kit reference range. On comparing to the Indian normative reference for the pregnant women, our results were not similar. However, the values were near similar to that of the American Thyroid Association guidelines.

CONCLUSIONS

We conclude our study results with a new reference range for the pregnant population in Manipur and also emphasis the use of trimester-specific reference range of thyroid hormone.

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

CONTEXT

Accurate assessment of thyroid function during pregnancy is critical, for initiation of thyroid hormone therapy, as well as for adjustment of thyroid hormone dose in hypothyroid cases.

AIMS

We evaluated pregnant women who had no past history of thyroid disorders and studied their thyroid function in each trimester.

SETTINGS AND DESIGN

86 normal pregnant women in the first trimester of pregnancy were selected for setting reference intervals. All were healthy, euthyroid and negative for thyroid peroxidase antibody (TPOAb). These women were serially followed throughout pregnancy. 124 normal nonpregnant subjects were selected for comparison.

MATERIAL AND METHODS

Thyrotropin (TSH), free thyroxine (FT4), free triiodothyronine (FT3) and anti-TPO were measured using Roche Elecsys 1010 analyzer. Urinary iodine content was determined by simple microplate method. The 2.5th and 97.5th percentiles were calculated as the reference intervals for thyroid hormone levels during each trimester.

STATISTICAL ANALYSIS

SPSS (version 14.0, SPSS Inc., Chicago, IL, USA) was used for data processing and analysis.

RESULTS

The reference intervals for the first, second and third trimesters for the following parameters: TSH 0.09-6.65, 0.51-6.66, 0.91-4.86 µIU/mL, FT4 9.81-18.53, 8.52-19.43, 7.39-18.28 pM/L and FT3 3.1-6.35, 2.39-5.12, 2.57-5.68 pM/L respectively. Thyroid hormone concentrations significantly differed during pregnancy at different stages of gestation. The pregnant women in the study had median urinary iodine concentration of 150-200 µg/l during each trimester.

CONCLUSIONS

The trimester-specific reference intervals for thyroid tests during pregnancy have been established for pregnant Indian women serially followed during pregnancy using 2.5th and 97.5th percentiles.

Gestational Age-specific Cut-off Values Are Needed for Diagnosis of Subclinical Hypothyroidism in Early Pregnancy

During the first trimester of pregnancy, thyroid-stimulating hormone (TSH) >2.5 mIU/L has been suggested as the universal criterion for subclinical hypothyroidism. However, TSH levels change continuously during pregnancy, even in the first trimester. Therefore the use of a fixed cut-off value for TSH may result in a different diagnosis rate of subclinical hypothyroidism according to gestational age. The objective of this study was to obtain the normal reference range of TSH during the first trimester in Korean gravida and to determine the diagnosis rate of subclinical hypothyroidism using the fixed cut-off value (TSH >2.5 mIU/L). The study population consisted of pregnant women who were measured for TSH during the first trimester of pregnancy (n=492) and nonpregnant women (n=984). Median concentration of TSH in pregnant women was lower than in non-pregnant women. There was a continuous decrease of median TSH concentration during the first trimester of pregnancy (median TSH concentration: 1.82 mIU/L for 3+0 to 6+6 weeks; 1.53 mIU/L for 7+0 to 7+6 weeks; and 1.05 mIU/L for 8+0 to 13+6 weeks). Using the fixed cut-off value of TSH >2.5 mIU/L, the diagnosis rate of subclinical hypothyroidism decreased significantly according to the gestational age (GA) at TSH (25% in 3+0 to 6+6 weeks, 13% in 7+0 to 7+6 weeks, and 9% for 8+0 to 13+6 weeks, P<0.001), whereas the diagnosis rate was 5% in all GA with the use of a GA-specific cut-off value (P=0.995). Therefore, GA-specific criteria might be more appropriate for the diagnosis of subclinical hypothyroidism.

Circadian and Circannual Rhythms in Thyroid Hormones: Determining the TSH and Free T4 Reference Intervals Based Upon Time of Day, Age, and Sex

BACKGROUND

Establishing the reference interval for thyrotropin (TSH) and free thyroxine (T4) is clinically important because a number of disease states have been linked to alterations in TSH and free T4 concentrations that are within the 95% confidence interval for normal thyroid hormone values. Age, sex, time of day, and ethnicity are known to affect circulating levels of TSH and free T4 but have not been used to establish reference intervals. The purpose of this study was to define the reference interval for TSH and free T4 taking into account age, sex, ethnicity, and circadian and circannual variability.

METHODS

We performed a retrospective analysis of 465,593 TSH and 112,994 free T4 measurements from subjects ages 1-104 years with no thyroid disease using a single TSH and free T4 immunoassay method. Boundaries for the central 95% of patient values, taking into account hour of day, day of year, sex, and age were calculated.

RESULTS

Females had significantly higher TSH and free T4 levels than males; the magnitude of these differences did not exceed 0.1 mIU/L or 0.1 ng/dL respectively. Although the 2.5% TSH reference interval remains constant through the day, date, and age ranges, the upper limit (97.5%) of the TSH reference interval increases from 6.45 to 7.55 mIU/L with age, due primarily to a progressive increase in the amplitude of the nocturnal TSH surge. Additionally, significant ethnic differences in TSH circadian periodicity occur between African American, Pacific Island, and Caucasian populations.

CONCLUSIONS

The reference interval for TSH varies significantly by age, sex, hour of day, and ethnicity. Time of year does not affect the TSH reference interval, and age, sex, hour of day and time of year do not affect the free T4 reference interval.

Prevalence of thyroid dysfunction among women during the first trimester of pregnancy at a tertiary care hospital in Haryana

BACKGROUND

Undetected and untreated thyroid disorders are associated with adverse maternal and fetal outcomes. There are limited data on the prevalence of newly diagnosed thyroid disease during pregnancy from India. Therefore, this study was designed to evaluate the prevalence of thyroid dysfunction, especially hypothyroidism during the first trimester of pregnancy.

MATERIALS AND METHODS

The present cross-sectional study was conducted at Department of endocrinology and antenatal clinic in the Obstetrics and Gynecology Pt. B.D. Sharma PGIMS, Rohtak over a period of 1-year. The total sample population comprised of 461 pregnant women with uncomplicated intrauterine singleton pregnancies in the first trimester of gestation without any history of thyroid disease or intake of any thyroid medication. Morning blood samples from the participants were analyzed for thyroid function tests, which included FT3, FT4, thyroid-stimulating hormone (TSH) and anti-thyroid peroxidase antibodies (TPO).

RESULTS

A total of 461 women were enrolled for this study. Mean maternal age was 23.79 ± 3.47 years. Median gestational age was 8 weeks 5 days. The median FT3, FT4 and TSH were 3.3 pg/mL, 1.25 ng/dL, and 1.40 mIU/L, respectively. Anti-TPO was elevated in 128 (27.8%) pregnant women. 99 (21.5%) women had sub-clinical hypothyroidism and 39 (39.4%) among them were positive for anti-TPO (P ≤ 0.001). 2 (0.4%) of women had overt hyperthyroidism, whereas 15 (3.3%) of the women had sub-clinical hyperthyroidism.

CONCLUSION

Considering the immense impact that maternal thyroid dysfunction has on maternal and fetal outcomes, prompt identification of thyroid dysfunction and its timely treatment is essential. Thus, universal screening of pregnant women for thyroid dysfunction should be considered especially in a country like India due to the high prevalence of thyroid dysfunction.

Obesity and risk of thyroid cancer: evidence from a meta-analysis of 21 observational studies

BACKGROUND

Several studies have evaluated the association between obesity and thyroid cancer risk. However, the results remain uncertain. In this study, we conducted a meta-analysis to assess the association between obesity and thyroid cancer risk.

MATERIAL/METHODS

Published literature from PubMed, EMBASE, Springer Link, Ovid, Chinese Wanfang Data Knowledge Service Platform, Chinese National Knowledge Infrastructure (CNKI), and Chinese Biology Medicine (CBM) were retrieved before 10 August 2014. We included all studies that reported adjusted risk ratios (RRs), hazard ratios (HRs) or odds ratios (ORs), and 95% confidence intervals (CIs) of thyroid cancer risk.

RESULTS

Thirty-two studies (n=12 620 676) were included in this meta-analysis. Obesity was associated with a significantly increased risk of thyroid cancer (adjusted RR=1.33; 95% CI, 1.24-1.42; I2=25%). In the subgroup analysis by study type, increased risk of thyroid cancer was found in cohort studies and case-control studies. In subgroup analysis by sex, both obese men and women were at significantly greater risk of thyroid cancer than non-obese subjects. When stratified by ethnicity, significantly elevated risk was observed in Caucasians and in Asians. In the age subgroup analysis, both young and old populations showed increased thyroid cancer risk. Subgroup analysis on smoking status showed that increased thyroid cancer risks were found in smokers and in non-smokers. In the histology subgroup analyses, increased risks of papillary thyroid cancer, follicular thyroid cancer, and anaplastic thyroid cancer were observed. However, obesity was associated with decreased risk of medullary thyroid cancer.

CONCLUSIONS

Our results indicate that obesity is associated with an increased thyroid cancer risk, except medullary thyroid cancer.

Establishment of Trimester-Specific Reference Intervals of Serum TSH & fT4 in a Pregnant Indian Population at North Kolkata

Reference intervals (RIs) of serum thyroid stimulating hormone (TSH) and free thyroxine (fT4) were determined in 402 healthy pregnant women by enzyme-linked immunosorbent assay (ELISA) technique after partitioning them into three trimesters. The reference population was chosen from a study population of 610 pregnant females by applying strict inclusion and exclusion criteria. The assays were done using proper quality control measures. RIs were calculated from the central 95 % of the distribution of TSH and fT4 values located between the lower reference limit of 2.5 percentile and upper reference limit of 97.5 percentile value 0.90 confidence intervals for the upper and lower reference limits were also determined. The reference intervals for TSH were 0.25-3.35 μIU/ml for the first trimester; 0.78-4.96 μIU/ml for the second trimester and 0.89-4.6 μIU/ml for the third trimester. Similarly, the reference intervals for fT4 for first, second and third trimesters were 0.64-2.0, 0.53-2.12 and 0.64-1.98 ng/dl respectively. The values thus obtained varied from those provided by the kit literature. In comparison to our derived reference intervals, the reference data from kit manufacturer under-diagnosed both subclinical hypo- and hyper-thyroidism within our pregnant reference population.

Trimester-specific reference ranges for thyroid hormones in Iranian pregnant women

Background. Due to many physiological changes during pregnancy, interpretation of thyroid function tests needs trimester-specific reference intervals for a specific population. There is no normative data documented for thyroid hormones on healthy pregnant women in Iran. The present survey was conducted to determine trimester-specific reference ranges for serum TSH, thyroxine (TT4), and triiodothyronine (TT3). Methods. The serum of 215 cases was analyzed for measurement of thyroid function tests by immunoassay method of which 152 iodine-sufficient pregnant women without thyroid autoantibodies and history of thyroid disorder or goiter were selected for final analysis. Reference intervals were defined as 5th and 95th percentiles. Results. Reference intervals in the first, second, and third trimesters were as follows: TSH (0.2–3.9, 0.5–4.1, and 0.6–4.1 mIU/l), TT4 (8.2–18.5, 10.1–20.6, and 9–19.4 μg/dl), and TT3 (137.8–278.3, 154.8–327.6, and 137–323.6 ng/dl), respectively. No correlation was found between TSH and TT4 or TT3. Significant correlation was found between TT4 and TT3 in all trimesters (r = 0.35, P < 0.001). Conclusion. The reference intervals of thyroid function tests in pregnant women differ among trimesters. Applying trimester-specific reference ranges of thyroid hormones is warranted in order to avoid misclassification of thyroid dysfunction during pregnancy.

Thyroid function in pregnant women: iodine deficiency after iodine enrichment program

OBJECTIVE

Significant changes in thyroid function occur during pregnancy which can complicate the interpretation of thyroid function tests. Therefore, normative gestational related reference ranges for thyroid hormones tests are required. The aim of this study was to determine the reference ranges for free triiodothyronine (FT3), free thyroxin (FT4) and thyroid stimulating hormone (TSH) in Iranian pregnant women.

METHODS

This study was a cross-sectional observational study conducted in the Obstetrics and Gynecology department, Akbarabadi University Hospital. A single blood sample from 584 pregnant women was analyzed for thyroid function. Serum levels of TSH, FT4, FT3, total T4 (TT4), T3 resin uptake (T3RU) and anti-thyroid peroxidase antibody (TPO Ab) were measured. Urinary iodine was determined in some cases. Reference intervals based on 2.5th and 97.5th percentiles were calculated.

RESULTS

The composition of reference population comprising 584 women included 162 in first trimester and 422 in the third trimester. The 2.5th and 97.5th percentiles values were used to determine the reference ranges for FT3, FT4, TT4, T3RU and TSH. These values were T3 1.4 and 2.9 pmol/L, FT4 7.1 and 18 pmol/L, TT4 7.2 and 13.5 µg/dL and TSH 0.5 and 3.9 µg/L, respectively. The level of urinary iodine in 80.5% of the subjects was less than normal.

CONCLUSIONS

Serum levels of thyroid hormones are different in Iranian population that could be due to racial differences or differences in iodine intake.

Establishment of the trimester-specific reference range for free thyroxine index

BACKGROUND

Accurate assessment of thyroid status during pregnancy is vital for maternal and fetal health. Because free thyroxine (FT4) values in pregnancy vary widely between methods, assessment of total T4 (TT4) and FT4 index (FT4I) may be superior to FT4 in pregnant women. However, trimester-specific reference intervals for FT4I have not yet been established. In this longitudinal self-sequential survey, we aimed at determining the trimester-specific reference range for FT4I in healthy Iranian women with singleton pregnancies.

METHODS

A total of 466 healthy pregnant women were evaluated. After exclusion of women with history, ultrasonographic, or laboratory evidence of any thyroid disorder or iodine deficiency and those who were positive for thyroid autoantibodies, 152 women entered the study. Serum thyrotropin (TSH), TT4, and triiodothyronine-resine uptake were measured by an immunoassay method. Reference intervals were defined as 5th and 95th percentiles, using the bootstrap-based procedure.

RESULTS

Mean values in the first, second, and third trimesters were 1.7±1.5, 1.9±1.8, and 1.9±1.8 mIU/L for TSH; 12.9±3, 14.4±3.1, and 13.6±3.3 μg/dL for TT4; and 12.8±3.5, 14.2±3.3, and 13.5±3.8 for FT4I, respectively. Reference intervals in the first, second, and third trimesters were as follows (respectively): TSH-0.2-3.9, 0.5-4.1, and 0.6-4.1 mIU/L; TT4-8.2-18.5, 10.1-20.6, and 9-19.4 μg/dL; and FT4I-8.5-19, 9.7-21, and 8.7-20.4. Serum TSH had no significant correlation with TT4. Serum TSH had a significant but weak correlation with FT4I only in the first trimester (r=-0.24, p=0.006).

CONCLUSION

This study, for the first time, establishes the trimester-specific reference intervals for FT4I in a reference population of normal iodine-sufficient pregnant Iranian women.

Gestational changes of thyroid function and urinary iodine in thyroid antibody-negative Japanese women

Iodine is an essential nutrient for thyroid hormone synthesis, and iodine deficiency especially in pregnant and lactating women results in serious damage to their infants. To characterize iodine nutrition throughout gestation by using a food frequency questionnaire (FFQ) and urinary iodine concentration (UIC) measurement, and to establish appropriate gestational age-specific reference ranges for serum TSH and FT₄ in thyroid autoantibody (ThAb) negative euthyroid Japanese women, a total number of 563 pregnant women including 422 subjects with negative ThAbs, 105 postpartum women and their 297 newborn infants were included in the study. Dietary iodine intake (DII) was evaluated by FFQ. Serum TSH, FT₄ and UIC were sequentially determined in the three trimesters of pregnancy and at the 31st postpartum day. The overall median UICs throughout pregnancy and in the postpartum period were 224.0 and 135.0 μg/L, respectively, suggesting sufficient iodine nutrition. The median DII was 842.4 μg/day in pregnant women. The median UIC in the first trimester (215.9 μg/L) significantly decreased in the second trimester (136.0 μg/L). The prevalence of pregnant women with a UIC below 150 μg/L was 31.6% and that in lactating women with a UIC below 100 μg/L was 33.3%. The pattern of gestational change in serum TSH and FT₄ was comparable to that in iodine-sufficient areas. A substantial percentage of women might be at risk for iodine deficiency if there is a restriction of iodine-rich foods. However, iodine supplementation for pregnant women must be carefully balanced against the risk of iodine excess particularly in Japan. Further research in larger samples is needed.

First- and Second-Trimester Reference Intervals for Thyroid Hormones during Pregnancy in "Rhea" Mother-Child Cohort, Crete, Greece

Estimation and interpretation of thyroid function tests in pregnant women is of utmost importance for maternal, fetal and neonatal health. Our objective was to calculate laboratory- and geography-specific reference intervals for thyroid hormones during pregnancy in an iodine-sufficient area of the Mediterranean, Crete, Greece. This project was performed in the context of “Rhea” mother-child cohort. Fulfillment of extensive questionnaires and estimation of free triiodothyronine (fT3), free thyroxine (fT4), thyroid-stimulating hormone (TSH), and antithyroid antibodies were performed. The reference population was defined using inclusion criteria regarding thyroidal, obstetric, and general medical status of women. Reference interval for TSH was 0.05–2.53 μIU/mL for the first and 0.18–2.73 μIU/mL for the second trimester. 6,8% and 5,9% of women in the first and second trimester, respectively, had TSH higher than the upper reference limit. These trimester-specific population-based reference ranges are essential in everyday clinical practice for the correct interpretation of thyroid hormone values and accurate classification of thyroid disorders.

Thyroid function and pregnancy: before, during and beyond

Thyroid disturbances are common in women during the reproductive years of their lives. Autoimmunity and altered iodine status together account for a high proportion of the abnormalities. Autoimmune thyroid disease is present in around 4% of young females, and up to 15% are at risk because they are thyroid antibody-positive. There is a strong relationship between thyroid immunity on the one hand and infertility, miscarriage, and thyroid disturbances in pregnancy and postpartum on the other hand. Suboptimal iodine status affects a large proportion of the world's population, and pregnancy further depletes iodine stores. There is controversy surrounding the degree to which iodine should be supplemented and the duration of supplementation. Recent studies have helped to clarify the relationship between maternal thyroid status and neuropsychological development of the child. The role of other environmental factors including smoking and selenium status is also now recognised. Universal screening for thyroid hormone abnormalities is not routinely recommended at present. However, measurement of thyroid function and autoantibodies should certainly be considered in those who are at high risk of thyroid disease and in those whose pregnancy is otherwise high risk. The practicing clinician needs to be aware of the thyroid changes which accompany pregnancy.

Challenges in interpretation of thyroid function tests in pregnant women with autoimmune thyroid disease

Physiological changes during gestation are important to be aware of in measurement and interpretation of thyroid function tests in women with autoimmune thyroid diseases. Thyroid autoimmune activity is decreasing in pregnancy. Measurement of serum TSH is the first-line screening variable for thyroid dysfunction also in pregnancy. However, using serum TSH for control of treatment of maternal thyroid autoimmunity infers a risk for compromised foetal development. Peripheral thyroid hormone values are highly different among laboratories, and there is a need for laboratory-specific gestational age-related reference ranges. Equally important, the intraindividual variability of the thyroid hormone measurements is much narrower than the interindividual variation (reflecting the reference interval). The best laboratory assessment of thyroid function is a free thyroid hormone estimate combined with TSH. Measurement of antithyroperoxidase and/or TSH receptor antibodies adds to the differential diagnosis of autoimmune and nonautoimmune thyroid diseases.

Is hyperthyroidism underestimated in pregnancy and misdiagnosed as hyperemesis gravidarum?

Thyroid changes are considered to be normal events that happen as a large maternal multiorganic adjustment to pregnancy. However, hyperthyroidism occurs in pregnancy with clinical presentation similar to hyperemesis gravidarum (HG) and pregnancy itself. Moreover, 10% of women with HG will continue to have symptoms throughout the pregnancy suggesting that the underlying cause might not be elevation of human chorionic gonadotropin in the first trimester. Variable frequency of both hyperthyroidism and HG worldwide might suggest the puzzlement of inclusion criteria for both diagnoses enhanced by the alternation of thyroid hormone levels assessed in normal pregnancy. Increased number of hyperthyroidism among women population without the expected rise in gestational hyperthyroidism encouraged us for creating the hypotheses that hyperthyroidism could be underestimated in normal pregnancy and even misdiagnosed as HG. This hypothesis, if confirmed, might have beneficial clinical implications, such as better detection of hyperthyroidism in pregnancies, application of therapy when needed with the reduction of maternal or fetal consequences.

A study to establish gestation-specific reference intervals for thyroid function tests in normal singleton pregnancy

OBJECTIVE

To establish gestation-specific reference intervals for thyroid function tests in normal singleton pregnancy.

STUDY DESIGN

Cross-sectional observational study performed in the Obstetric and Gynaecology department, West Middlesex University Hospital. A single blood sample from 335 pregnant women at various gestations of pregnancy was analysed for thyroid function. FT4, fT3, TSH values at each gestation of pregnancy were calculated.

RESULTS

From the fT3, fT4 and TSH results, a 95% reference interval was calculated for each hormone for each week of pregnancy.

CONCLUSION

We calculated gestation-specific reference intervals for thyroid function tests throughout pregnancy to facilitate clinical management of thyroid disease in pregnancy.

[Reference interval of serum thyroid hormones in healthy Korean adults]

OBJECTIVES

This study was conducted to determine the reference interval of serum thyroid hormones (TSH, FT3, FT4) in healthy Korean adults.

METHODS

Health examination data from 1,591 healthy Korean adults who visited an university hospital were analyzed. Patients with specific health conditions capable of altering laboratory results were excluded from the study. Serum thyroid hormones were measured using IMMULITE 2000 (DPC, USA, 2002). Subjects were 18-65 years old; 911 were male, and 690 were female.

RESULTS

The arithmetic means of TSH, FT3, and FT4 values for male subjects were 1.28+/-1.84 microIU/ml, 3.23+/-0.57 pg/ml, and 1.42+/-0.22 ng/dl, respectively. In female subjects, the arithmetic means of TSH, FT3, and FT4 values were 1.49+/-2.08 microIU/ml, 3.08+/-0.54 pg/ml, and 1.29 +/-0.24 ng/dl, respectively. The arithmetic mean FT4 value for males decreased with age (p<0.01). The arithmetic mean FT3 value for females increased with age (p<0.01). The arithmetic mean thyroid hormone values of all study subjects differed significantly based on season. The arithmetic mean of male FT4 decreased with increasing BMI (p<0.01). The arithmetic mean of female FT3 increased with increasing BMI (p<0.01). The reference intervals recommended by the IMMULITE 2000 manufacturer are 0.40-4.00 microIU/ml for TSH, 1.80-4.20 pg/ml for FT3, and 0.80-1.90 ng/dl for FT4 (same values for both genders).

CONCLUSIONS

There was a significant difference in the interval of thyroid hormones between males and females, but the reference interval of IMMULITE 2000 was not established by gender. There is a need to reestablish the reference interval for thyroid hormones in Korean healthy adults.

Establishment of reference range for thyroid hormones in normal pregnant Indian women

BACKGROUND

Interpretation of thyroid function tests during pregnancy needs trimester-related reference intervals from pregnant populations with minimal risk for thyroid dysfunction. While India has become iodine sufficient after two decades of salt iodisation, there is no normative data for thyroid function from healthy pregnant women of this country.

AIMS AND OBJECTIVES

To determine trimester-specific reference ranges for free triiodothyronine (FT(3)), free thyroxine (FT(4)) and thyrotropin (TSH) from healthy pregnant Indian women.

DESIGN

Cross-sectional study in a reference population of pregnant women.

SETTING

Primary care level obstetric department in India.

POPULATION

Women with uncomplicated pregnancy in any trimester.

METHODS

Five hundred and forty-one apparently healthy pregnant women with uncomplicated single intrauterine gestations reporting to the Armed Forces Clinic in any trimester were consecutively recruited. Clinical examination, thyroid ultrasound for echogenicity and nodularity and estimation of FT(3), FT(4), TSH and antithyroid antibodies (antithyroperoxidase [anti-TPO] and antithyroglobulin [anti-Tg]) using electrochemiluminescence technique were carried out. From this entire sample, a disease- and risk-free reference population was obtained by excluding those with any known factor that could affect thyroid function or those who were being treated for thyroid dysfunction.

MAIN OUTCOME MEASURE

None.

RESULTS

Of the 541 consecutive pregnant women in different trimesters enrolled for the study, 210 women were excluded. The composition of reference population comprising 331 women was 107 in first trimester, 137 in second trimester and 87 in third trimester. The 5th and 95th percentiles values were used to determine the reference ranges for FT(3), FT(4) and TSH. The trimester-wise values in the first, second and third trimesters were: FT(3) (1.92-5.86, 3.2-5.73 and 3.3-5.18 pM/l), FT(4) (12-19.45, 9.48-19.58 and 11.32-17.7 pM/l) and TSH (0.6-5.0, 0.44-5.78 and 0.74-5.7 iu/ml), respectively. Analysis of mean, median values for FT(3), FT(4) and TSH between each trimester showed no significant difference in FT(3) and TSH values (95% CI). However, FT(4) showed significant variation between trimesters with values decreasing with advancing gestational age (P value: first versus second = 0.015, first versus third = 0.003 and second versus third = not significant). Women with antibody positivity and hypoechogenicity of thyroid gland had significantly higher TSH values when compared with women with antibody negativity and normoechogenicity.

CONCLUSIONS

Reference ranges of FT(3), FT(4) and TSH have been established for pregnant Indian women using 5th and 95th percentiles.

Gestation-specific thyroxine and thyroid stimulating hormone levels in the United States and worldwide

BACKGROUND

Euthyroid women experience dramatic changes in the demand for thyroid hormone production as early as the first trimester of pregnancy. These changes are important for fetal neurodevelopment and organ development as well as maternal health and succesful full term pregnancy. Therefore, gestation-specific reference intervals assist in appropriate clinical management of thyroid disease in pregnancy to ensure maternal and fetal health.

OBJECTIVE

To determine trimester-specific levels of serum thyroxine (T4) and thyroid stimulating hormone (TSH) in the U.S. population based on the National Health and Nutrition Survey III and compare these with published trimester-specific T4 and TSH means and medians obtained in other countries worldwide.

METHODS

Trimester-specific means and medians for T4 and TSH were determined for the U.S. population based on the National Health and Nutrition Survey III database (1988-1994). These were compared with trimester-specific means and medians of other countries in the published literature.

RESULTS

Mean serum T4 levels for the U.S. population were 141.35, 152.95, and 142.65 nmol/L in the three trimesters, respectively, whereas mean serum TSH levels were 0.91, 1.03, and 1.32 mIU/L.

CONCLUSIONS

Gestation-specific mean T4 and TSH levels for the representative U.S. population are well within the trimester-specific reference intervals. T4 and TSH measured during pregnancy in longitudinal and cross-sectional studies of populations worldwide demonstrate that, in some populations, T4 and TSH levels are outside the normal trimester-specific reference intervals.

Tandem mass spectrometry improves the accuracy of free thyroxine measurements during pregnancy

OBJECTIVE

Pregnancy is a time of rapidly changing demands on the thyroid axis, and knowledge of thyroid hormone levels, especially during the first trimester, is important for ensuring maternal and fetal health. The thyroid hormone assays currently in use become more inaccurate at extremes of binding protein concentrations and when heterophilic antibodies are present. Pregnancy is characterized by both these conditions, making accurate determination of free thyroid hormone levels by conventional direct analog immunoassay methods difficult. The objective of this study was to characterize the performance of a novel tandem mass spectrometric assay for free thyroxine during the physiologic conditions of pregnancy.

DESIGN

Healthy women without a history of thyroid abnormalities were recruited from the obstetrics and gynecology and endocrinology clinics of a university medical center and their thyroid status was monitored. Free thyroxine levels were assessed by both immunoassay and tandem mass spectrometry during the course of their pregnancy. Serum thyrotropin levels were also measured. The distributions of free thyroid concentrations obtained by the two assays were compared.

MAIN OUTCOME

The tandem mass spectrometry and immunoassay values did not correlate well with each other. However, tandem mass spectrometry values correlated well with the current gold standard equilibrium dialysis values. Moreover, the good agreement between equilibrium dialysis and tandem mass spectrometry was maintained across all weeks of gestation.

CONCLUSIONS

We conclude that tandem mass spectrometry has a superior performance to immunoassay for the measurement of free thyroxine during pregnancy. Furthermore, it is ideally suited to generating trimester-specific reference intervals for free thyroxine levels. Future studies will determine if it is a better assay to use in most clinical circumstances.

Thyroid medications during pregnancy

Euthyroid women experience dramatic changes in their thyroid physiology in order to accommodate the presence of placental and fetal tissues. These adaptations to the pregnant state make it crucial to develop reliable trimester-specific intervals for thyroid parameters. Use of non-pregnant reference intervals could lead to erroneous assessment of thyroid status in this rapidly changing hormonal environment. Only with a full appreciation of physiologic changes in thyroid parameters during a euthyroid pregnancy, can thyroid dysfunction be appropriately diagnosed and managed. Iodine sufficiency during pregnancy can be achieved with supplementation using a multivitamin. Both hypothyroidism and hyperthyroidism should be diagnosed using the appropriate reference intervals for pregnancy. Hypothyroid women are best treated with a specific brand of levothyroxine. Hypothyroidism should ideally be treated prior to conception. If newly recognized during pregnancy, it should be fully treated as early as possible. Frequent monitoring of thyroid status is essential as many women demonstrate an increased requirement for thyroid hormone during the first trimester. Although mild hyperthyroidism may be well tolerated during pregnancy, overt hyperthyroidism requires treatment. Thionamides are the mainstay of therapy. Following their initiation, close monitoring is required to avoid maternal and fetal hypothyroidism. There are occasional circumstances when other medical therapy or surgical therapy may be employed for hyperthyroidism. Thyroidectomy is generally safe in the second trimester in an appropriately prepared woman. There is limited data about the role and safety of oral contrast agents, iodine, amiodarone, and perchlorate. Radioiodine therapy is contradicted during pregnancy.

Association between the severity of Hashimoto's disease and the functional +874A/T polymorphism in the interferon-gamma gene

CD8+ CD25+-activated cytotoxic T cells and anti-thyroglobulin antibodies (TgAb) are independently involved in the severity of Hashimoto's disease (HD). Interferon gamma (IFN-gamma) activates cytotoxic T cells. To evaluate the hypothesis that the functional +874A/T polymorphism in the gene encoding IFN-gamma is associated with the severity of HD, we examined the frequencies of this polymorphism in 34 HD patients who developed hypothyroidism (severe HD); 22 untreated, euthyroid HD patients (mild HD); 49 patients with intractable Graves' disease (GD); 16 GD patients in remission; and 57 healthy volunteers. Frequency of the +874T allele, which is associated with high IFN-gamma production, was higher in patients with severe HD than in those with mild HD (odds ratio [OR], 3.5; 95% confidence interval [CI], 1.0-12.4; p = 0.047), but there was no difference in the frequency between GD patients. The difference in the frequency of +874T was observed in the subset of patients with HD negative for TgAb (OR, 8.4; 95% CI, 1.2-57.3; p = 0.029) but not in the subset of patients with HD positive for TgAb. Our data indicate that the +874A/T polymorphism in the IFN-gamma gene is associated with severity of HD.

Thyroid hormones status during pregnancy in normal Iranian women

Pregnancy is associated with significant, but reversible changes in thyroid function studies, which are among the most profound seen as a result of a normal physiologic state. The present study was carried out to find out alterations in thyroid function tests in each trimester in normal pregnant women as compared to non-pregnant women in Tabriz-Iran. A case-control study designed with 229 normal pregnant women that randomly selected from the first (64 samples), the second (92 samples), and the third (73 samples) trimesters and 250 randomly selected non-pregnant healthy female controls. Age range in both groups was 16-40 years. Thyroid function tests carried out by measuring serum levels of thyroid stimulating hormone (TSH), free and total thyroxin (FT(4), TT(4)), and free and total triiodothyronine (FT(3), TT(3)) by commercially available radio immunoassay kits. We found that mean TT(4) increased progressively during pregnancy. Our study showed increasing in serum levels of TT(3) in the second trimester and then declining during the third trimester compared with non-pregnant women. We showed that FT(4) strongly decreased during the third trimester. Free T(3) showed declining in the second and third trimesters. Mean TSH did not show significant difference in each trimester compared with non-pregnant women. The thyroid function tests in pregnancy should be interpreted against gestational age-related reference intervals to avoid mis-interpretation of thyroid function during pregnancy.