Gestational age-specific reference ranges from different laboratories misclassify pregnant women's thyroid status: comparison of two longitudinal prospective cohort studies

Defining Gestational Thyroid Dysfunction Through Modified Nonpregnancy Reference Intervals: An Individual Participant Meta-analysis

BACKGROUND

Establishing local trimester-specific reference intervals for gestational TSH and free T4 (FT4) is often not feasible, necessitating alternative strategies. We aimed to systematically quantify the diagnostic performance of standardized modifications of center-specific nonpregnancy reference intervals as compared to trimester-specific reference intervals.

METHODS

We included prospective cohorts participating in the Consortium on Thyroid and Pregnancy. After relevant exclusions, reference intervals were calculated per cohort in thyroperoxidase antibody-negative women. Modifications to the nonpregnancy reference intervals included an absolute modification (per .1 mU/L TSH or 1 pmol/L free T4), relative modification (in steps of 5%) and fixed limits (upper TSH limit between 3.0 and 4.5 mU/L and lower FT4 limit 5-15 pmol/L). We compared (sub)clinical hypothyroidism prevalence, sensitivity, and positive predictive value (PPV) of these methodologies with population-based trimester-specific reference intervals.

RESULTS

The final study population comprised 52 496 participants in 18 cohorts. Optimal modifications of standard reference intervals to diagnose gestational overt hypothyroidism were -5% for the upper limit of TSH and +5% for the lower limit of FT4 (sensitivity, .70, CI, 0.47-0.86; PPV, 0.64, CI, 0.54-0.74). For subclinical hypothyroidism, these were -20% for the upper limit of TSH and -15% for the lower limit of FT4 (sensitivity, 0.91; CI, 0.67-0.98; PPV, 0.71, CI, 0.58-0.80). Absolute and fixed modifications yielded similar results. CIs were wide, limiting generalizability.

CONCLUSION

We could not identify modifications of nonpregnancy TSH and FT4 reference intervals that would enable centers to adequately approximate trimester-specific reference intervals. Future efforts should be turned toward studying the meaningfulness of trimester-specific reference intervals and risk-based decision limits.

Levothyroxine for subclinical hypothyroidism during pregnancy: an updated systematic review and meta-analysis of randomized controlled trials

PURPOSE

We aimed to perform a systematic review and meta-analysis addressing the efficacy of levothyroxine therapy in pregnant women with subclinical hypothyroidism considering most recent evidence and subgroups of interest for clinical practice.

METHODS

PubMed, Embase, and Cochrane Central were searched from inception for randomized controlled trials (RCTs) comparing levothyroxine with placebo or no intervention in pregnant women with subclinical hypothyroidism. We used a random-effects model and conducted subgroup analyses based on thyroid peroxidase antibody status, thyroid stimulating hormone levels, fertility treatment, and recurrent miscarriage.

RESULTS

We included 11 RCTs comprising 2,749 pregnant women with subclinical hypothyroidism. Patients treated with levothyroxine (1,439; 52.3%) had significantly lower risk of pregnancy loss (risk ratio 0.69; 95% confidence interval 0.52-0.91; p < 0.01; 6 studies). However, there was no significant association between levothyroxine and live birth (risk ratio 1.01; 95% confidence interval 0.99-1.03; p = 0.29; 8 studies). No statistically significant interaction was observed across subgroups (p > 0.05).

CONCLUSION

Levothyroxine replacement therapy for subclinical hypothyroidism during pregnancy may decrease pregnancy loss when early prescribed. Nevertheless, further investigation is needed in patients with thyroid stimulating hormone above four milliunits per liter, especially when associated with recurrent miscarriage or infertility.

Developmental scores in offspring of women with subclinical hypothyroidism in pregnancy are affected by gender and thyrotropin cutoff

OBJECTIVES

Subclinical hypothyroidism (SCH) is defined by elevated thyrotropin (TSH) and normal level of thyroxine (T4). The definition of SCH and the cutoff for TSH normality in pregnancy are debated. In the present study, we assess offspring perinatal outcome, anthropometrics and early development in relation to different TSH levels.

METHODS

An observational study with 77 singleton-pregnant women included by thyroid screening before a planned cesarean section. Two TSH-cutoffs (3.0 and 3.7 mIU/L) defined euthyroid and SCH groups, and were applied to evaluate offspring anthropometrics, complication rates (maternal blood loss, Apgar-score, cord arterial-pH, admission to neonatal intensive care unit, perinatal hypoglycemia) and offspring development. Development was evaluated by Bayley-III test in a subsample at age 6 months (n=27) and 15 months (n=22).

RESULTS

Prevalence of SCH was 31.2 % at TSH-cutoff 3.0 mIU/L, and 16.9 % at TSH-cutoff 3.7 mIU/L. No differences in complications and anthropometrics were observed. In Bayley-III tests, cognitive score was decreased at 6 months (p=0.012) and at 15 months (p=0.056) by applying TSH-cutoff 3.0 mIU/L. At cutoff 3.7 mIU/L, motor score was decreased at 15 months (p=0.020). Male offspring had significantly lower cognitive scores at age 6 and 15 months (TSH-cutoff 3.0 mIU/L), and motor scores at age 15 months (TSH-cutoff 3.7 mIU/L).

CONCLUSIONS

The importance of the definition of thyroid normality in pregnancy is underlined. This study suggests that a gender-effect might be present in maternal thyroid disease, and that developmental differences exist if TSH-cutoff is low. Further research is needed.

Subclinical hypothyroidism in pregnancy - assessment of offspring thyroid status and mitochondrial robustness to stress

Subclinical hypothyroidism's clinical implications on pregnancy are controversial. Consequently, thyrotropin (TSH) cutoff-values for pregnancy are continuously a subject for debate. In subclinical hypothyroidism, altered levels of thyroid hormones may affect mitochondrial function.Objectives were i) to analyze thyroid hormone levels in offspring of women with and without subclinical hypothyroidism ii) to analyze mitochondrial "robustness" in terms of MTG/TMRM ratio in pregnant women and their offspring in relation to thyroid function and iii) to perform differentiate analyses on different TSH thresholds to determine the importance of cutoff-values to results.Pregnant women were included by blood collections prior to a planned cesarean section, and cord samples were collected after delivery. Thyroid status (analyzed by Siemens Healthcare Diagnostics by an electrochemical luminescent immunoassay based on LOCI-technology) grouped the women and their offspring in euthyroid or subclinical hypothyroid, with groups established from previous recommended third-trimester cutoff-value (TSH > 3.0 mIU/L) and the recently recommended cutoff-value in Denmark (TSH > 3.7 mIU/L). Flow cytometric measurements of mitochondrial function in mononuclear blood cells with the fluorophores TetraMethylRhodamine Methyl Ester (TMRM) and Mitotracker Green (MTG) were used to evaluate mitochondrial robustness as the MTG/TMRM ratio.No significant differences in mitochondrial robustness between euthyroid and subclinical hypothyroid cohorts were observed, irrespective of TSH-cutoff applied. Maternal and cord MTG/TMRM ratios were positively correlated. Cord-TSH was elevated in subclinical hypothyroid offspring, independent of TSH cutoff applied. Cord-TSH was associated with maternal TSH-level, maternal smoking and cord arterial-pH.

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.

Pregnancy disrupts the accuracy of automated fT4 immunoassays

Objective

Thyroid hormone measurements are often performed in pregnant women, as hypo- and hyperthyroidism during pregnancy can severely affect the fetus. Serum free thyroxine (fT4) measurements are well known for their analytical challenges, due to low serum concentrations and the subtle equilibrium between free and bound T4 (to thyroid-binding globulin (TBG), transthyretin and albumin). Pregnant women have high TBG concentrations due to an increase in human chorionic gonadotropin (hCG) and estrogen and lower albumin concentrations which change the equilibrium and may affect the validity of fT4 measurements in their samples. As accurate serum fT4 measurements in pregnant women are important for the long-term health of the fetus, we aimed to evaluate the accuracy of several fT4 immunoassays in the serum of pregnant women.

Methods

FT4 was measured in healthy controls and pregnant women using a candidate-reference method (LC-MS/MS) and five commercially available automated immunoassays (Alinity (Abbott), Atellica (Siemens), Cobas (Roche), Lumipulse (Fujirebio) and UniCel DXI (Beckman Coulter)). Method comparisons (Bland Altman plots and Passing and Bablok analyses) were performed.

Results

Serum samples from both healthy controls (n = 30) and pregnant women (n = 30; mean gestational age, 24.8 weeks) were collected. The fT4 immunoassays deviated +7 to +29% more from the LC-MS/MS in serum samples of pregnant women than healthy controls (falsely high).

Conclusions

Our results indicate that immunoassays overestimate fT4 in pregnant women, which might lead to an overestimation of thyroid status. Physicians and laboratory specialists should be aware of this phenomenon to avoid drawing false conclusions about thyroid function in pregnant women.

Maternal hypothyroidism and adverse outcomes of pregnancy

OBJECTIVE

Hypothyroidism has been associated with pregnancy complications, but uncertainty prevail regarding the severity and the role of thyroid autoimmunity. This study aimed to evaluate adverse pregnancy outcomes by exposure to maternal hypothyroidism and thyroid autoimmunity.

DESIGN

Retrospective cohort study.

PATIENTS

14,744 singleton pregnancies from the North Denmark Region Pregnancy Cohort (2011-2015).

MEASUREMENTS

Maternal thyroid stimulating hormone (TSH), thyroid peroxidase antibodies (TPO-Ab), and thyroglobulin antibodies (Tg-Ab) were retrospectively measured in early pregnancy blood samples (ADVIA Centaur XPT, Siemens Healthineers). Adjusted odds ratio (aOR) with 95% confidence interval (CI) was used to estimate associations between maternal hypothyroidism (TSH cut-offs: 6.0 and 10 mIU/L), thyroid autoimmunity (TPO-Ab cut-off: 60 U/ml, Tg-Ab cut-off: 33 U/ml), and adverse pregnancy outcomes.

RESULTS

Pregnancy outcomes were 93.2% live births, 6.5% spontaneous abortions, and 0.3% stillbirths. The frequency of spontaneous abortion was 6.5% when TSH was below 6.0 mIU/L, 6.5% when above 6.0 mIU/L (aOR 1.0 [95% CI: 0.5-2.0]), and 12.5% when above 10 mIU/L (aOR: 2.0 [95% CI: 0.8-5.2]). For outcome of preterm birth, the frequency was 5.4% when TSH was below 6.0 mIU/L, 7.8% when above 6.0 mIU/L (aOR 1.5 [95% CI: 0.7-2.9]), and 11.4% when above 10 mIU/L (aOR: 2.6 [95% CI: 0.9-7.3]). No association was found between thyroid autoantibodies and spontaneous abortion (TPO-Ab: aOR: 1.0 [0.8-1.3], Tg-Ab: 1.0 [0.8-1.2]) or preterm birth (TPO-Ab: aOR: 1.0 [0.8-1.2], Tg-Ab: 0.9 [0.7-1.2]).

CONCLUSION

A high frequency of adverse pregnancy outcomes was seen among pregnancies exposed to maternal TSH above 10 mIU/L, whereas no association with thyroid autoantibodies was seen.

Association of Thyroid Peroxidase Antibodies and Thyroglobulin Antibodies with Thyroid Function in Pregnancy: An Individual Participant Data Meta-Analysis

Objectives: Thyroid autoimmunity is common in pregnant women and associated with thyroid dysfunction and adverse obstetric outcomes. Most studies focus on thyroid peroxidase antibodies (TPOAbs) assessed by a negative-positive dichotomy and rarely take into account thyroglobulin antibodies (TgAbs). This study aimed at determining the association of TPOAbs and TgAbs, respectively, and interdependently, with maternal thyroid function. Methods: This was a meta-analysis of individual participant cross-sectional data from 20 cohorts in the Consortium on Thyroid and Pregnancy. Women with multiple pregnancy, pregnancy by assisted reproductive technology, history of thyroid disease, or use of thyroid interfering medication were excluded. Associations of (log2) TPOAbs and TgAbs (with/without mutual adjustment) with cohort-specific z-scores of (log2) thyrotropin (TSH), free triiodothyronine (fT3), total triiodothyronine (TT3), free thyroxine (fT4), total thyroxine (TT4), or triiodothyronine:thyroxine (T3:T4) ratio were evaluated in a linear mixed model. Results: In total, 51,138 women participated (51,094 had TPOAb-data and 27,874 had TgAb-data). Isolated TPOAb positivity was present in 4.1% [95% confidence interval, CI: 3.0 to 5.2], isolated TgAb positivity in 4.8% [CI: 2.9 to 6.6], and positivity for both antibodies in 4.7% [CI: 3.1 to 6.3]. Compared with antibody-negative women, TSH was higher in women with isolated TPOAb positivity (z-score increment 0.40, CI: 0.16 to 0.64) and TgAb positivity (0.21, CI: 0.10 to 0.32), but highest in those positive for both antibodies (0.54, CI: 0.36 to 0.71). There was a dose-response effect of higher TPOAb and TgAb concentrations with higher TSH (TSH z-score increment for TPOAbs 0.12, CI: 0.09 to 0.15, TgAbs 0.08, CI: 0.02 to 0.15). When adjusting analyses for the other antibody, only the association of TPOAbs remained statistically significant. A higher TPOAb concentration was associated with lower fT4 (p < 0.001) and higher T3:T4 ratio (0.09, CI: 0.03 to 0.14), however, the association with fT4 was not significant when adjusting for TgAbs (p = 0.16). Conclusions: This individual participant data meta-analysis demonstrated an increase in TSH with isolated TPOAb positivity and TgAb positivity, respectively, which was amplified for individuals positive for both antibodies. There was a dose-dependent association of TPOAbs, but not TgAbs, with TSH when adjusting for the other antibody. This supports current practice of using TPOAbs in initial laboratory testing of pregnant women suspected of autoimmune thyroid disease. However, studies on the differences between TPOAb- and TgAb-positive women are needed to fully understand the spectrum of phenotypes.

Classification of maternal thyroid function in early pregnancy using repeated blood samples

Objective

The assessment of maternal thyroid function in early pregnancy is debated. It is well-established that pregnancy-specific reference ranges preferably should be used. We speculated if the use of repeated blood samples drawn in early pregnancy would influence the classification of maternal thyroid function.

Methods

Pregnant women with repeated early pregnancy blood samples were identified in the North Denmark Region Pregnancy Cohort. Each sample was used for the measurement of TSH, free T4 (fT4), thyroid peroxidase antibodies (TPO-Ab), and thyroglobulin antibodies (Tg-Ab) (ADVIA Centaur XPT, Siemens Healthineers). Method- and pregnancy week-specific reference ranges were used for the classification of maternal thyroid function.

Results

Among 1466 pregnancies included, 89 women had TSH above the upper reference limit in the first sample (median pregnancy week 8) and 44 (49.4%) of these similarly had high TSH in the second sample (median week 10). A total of 47 women had TSH below the lower reference limit in the first sample and 19 (40.4%) of these similarly had low TSH in the second sample. Regarding women classified with isolated changes in fT4 in the first sample, less than 20% were similarly classified as such in the second sample. The percentage agreement between the samples was dependent on the level of TSH in the first sample and the presence of TPO- and Tg-Ab.

Conclusion

In a large cohort of pregnant women, the classification of maternal thyroid function varied considerably with the use of repeated blood samples. Results emphasize a focus on the severity of thyroid function abnormalities in pregnant women.

Classification of Thyroid Dysfunction in Pregnant Women Differs by Analytical Method and Type of Thyroid Function Test

CONTEXT

Physiological alterations challenge the assessment of maternal thyroid function in pregnancy. It remains uncertain how the reference ranges vary by week of pregnancy, and how the classification of disease varies by analytical method and type of thyroid function test.

DESIGN

Serum samples from Danish pregnant women (n = 6282) were used for the measurement of thyrotropin (TSH), total and free thyroxine (T4), total and free 3,5,3'-triiodothyronine (T3), and T-uptake using "Method A" (Cobas 8000, Roche Diagnostics). TSH and free T4 were also measured using "Method B" (ADVIA Centaur XP, Siemens Healthineers).

MAIN OUTCOME MEASURES

Pregnancy week- and method-specific reference ranges were established among thyroid antibody-negative women (n = 4612). The reference ranges were used to classify maternal thyroid function, and results were compared by analytical method and type of thyroid function test.

RESULTS

The reference ranges for TSH showed a gradual decrease during pregnancy weeks 4 to 14, a gradual increase was observed for total T4, total T3, and T-uptake, whereas free T4 and free T3 showed less variation. When TSH and free T4 were used, Method A classified 935 (14.9%) with abnormal thyroid function, Method B a total of 903 (14.4%), and the methods agreed on 554 individuals. When TSH and total T4 were used, 947 (15.1%) were classified with abnormal thyroid function, and classifications by either total T4 or free T4 agreed on 584 individuals.

CONCLUSIONS

Even when pregnancy week- and method-specific reference ranges were established, the classification of maternal thyroid dysfunction varied considerably by analytical method and type of thyroid function test.

Turning to Thyroid Disease in Pregnant Women

Thyroid disease in pregnant women needs attention from a clinical and scientific standpoint due to the potential severe adverse consequences. It is well-established that overt thyroid disease in pregnant women should be treated to prevent maternal and fetal complications, but routine testing for overt thyroid function test abnormalities has not been implemented. In contrast, the scientific focus has shifted towards smaller aberrations in maternal thyroid function including subclinical thyroid disease and isolated deviations in maternal thyroxine. In this focused review, we touch upon the assessment of maternal thyroid function in pregnancy and how the historical advancements in thyroid function tests parallel with the thyroid function test abnormalities described. Furthermore, we discuss how the scientific focus has evolved and how the field could turn in view of the existing discrepancies between results of observational studies and randomized controlled trials.

Thyroid function abnormalities and thyroid autoantibodies in Danish pregnant women

OBJECTIVE

Abnormal thyroid function in pregnant women is a matter of concern. Knowledge on the occurrence of known and unidentified thyroid function abnormalities in a large unselected cohort of pregnant women is warranted as part of the debate on benefits and risks of routine testing.

DESIGN

Cohort study.

PARTICIPANTS

A total of 14 323 pregnant women in the North Denmark Region, who had a blood sample drawn as part of the prenatal screening program in early pregnancy (2011-2015).

MEASUREMENTS

TSH, free thyroxine, thyroid peroxidase and thyroglobulin antibodies were measured in the stored blood samples using an automatic immunoassay (ADVIA Centaur XPT, Siemens Healthineers). Cohort-, method- and week-specific reference ranges were used for classification of maternal thyroid function, and a cut-off of 60 U/mL was used for thyroid autoantibodies. Information in Danish nationwide registers was used to identify diagnosed and treated maternal thyroid disease.

RESULTS

Overall, 15.2% had thyroid function abnormalities in the early pregnancy and 14.9% were thyroid peroxidase and/or thyroglobulin antibody positive. Among women with known thyroid disease (n = 365), the frequency of abnormal thyroid function was 45.7%, and 62.8% in women (n = 172) who received current treatment in the pregnancy. When maternal thyroid disease was diagnosed in the years following pregnancy (n = 313), 46.7% had abnormal thyroid function and 54.3% were thyroid peroxidase and/or thyroglobulin antibody positive in the early pregnancy.

CONCLUSION

Thyroid function abnormalities and thyroid autoantibodies were common in Danish pregnant women, particularly in women with known or later diagnosed thyroid disease, which raises concern about inadequately treated and unidentified abnormal thyroid function.

Management of thyrotoxicosis during pregnancy

Thyrotoxicosis during pregnancy should be adequately managed and controlled to prevent maternal and fetal complications. The evaluation of thyroid function in pregnant women is challenged by the physiological adaptations associated with pregnancy, and the treatment with antithyroid drugs (ATD) raises concerns for the pregnant woman and the fetus. Thyrotoxicosis in pregnant women is mainly of autoimmune origin, and the measurement of thyroid stimulating hormone-receptor antibodies (TRAb) plays a key role. TRAb helps to distinguish the hyperthyroidism of Graves' disease from gestational hyperthyroidism in early pregnancy, and to evaluate the risk of fetal and neonatal hyperthyroidism in late pregnancy. Furthermore, the measurement of TRAb in early pregnancy is recommended to evaluate the need for ATD during the teratogenic period of pregnancy. Observational studies have raised concern about the risk of birth defects associated with the use of ATD in early pregnancy and challenged the clinical management and choice of treatment.

Thyroid Screening During Early Pregnancy and the Need for Trimester Specific Reference Ranges: A Cross-Sectional Study in Lahore, Pakistan

Background

Derangements in thyroid hormone levels can cause multiple complications in the mother and the foetus. Thyroid stimulating hormone (TSH) and free thyroxine (free T4 or FT4) levels are used to screen for maternal thyroid dysfunction; these should be compared with population based trimester-specific reference ranges. Our goal was: to determine the prevalence of various thyroid derangements, in early pregnancy, according to the current reference ranges available; to determine the need for trimester specific reference ranges for the local population.

Methods

A multi-centric, cross sectional population survey was conducted in Lahore, Pakistan. Serum TSH and FT4 levels were measured at the hormone lab of the Pathology department of Combined Military Hospital (CMH) Lahore. The results were entered and analysed using Statistical Package for the Social Sciences (SPSS) version 23. 

Results

In the 293 women sampled, mean FT4 and TSH levels were 15.03 (±5.62) pmol/L and 2.53 (±6.82) mIU/L respectively. According to the laboratory specific reference ranges, the prevalence of overt hyperthyroidism was 4.10%, (mean TSH= 0.03mIU/L); subclinical hyperthyroidism was 16.38%, (mean TSH= 0.17mIU/L); normal 70.65%, (mean TSH = 1.29mIU/L); subclinical hypothyroidism 4.44%, (mean TSH= 15.11mIU/L); overt hypothyroidism 4.44%, (mean TSH = 20.60mIU/L).

Conclusion

Our study showed a significant prevalence of thyroid dysfunction in the first trimester of pregnancy, and therefore highlights the need for more rigorous thyroid screening of women, in early pregnancy. There is a need to monitor these women in order to reduce maternal and foetal complications. Trimester specific reference ranges for thyroid hormones need to be developed in Pakistan.

Pregnancy Week-Specific Reference Ranges for Thyrotropin and Free Thyroxine in the North Denmark Region Pregnancy Cohort

BACKGROUND

Physiological changes in maternal thyroid function during pregnancy necessitate the use of pregnancy-specific reference ranges. Dynamic changes in thyrotropin (TSH) within the first trimester of pregnancy have been reported, but more evidence is needed to substantiate the findings. The objective of this study was to estimate pregnancy week-specific reference ranges for maternal TSH and free thyroxine (fT4) in early pregnancy.

METHODS

The study consecutively recruited serum residues from blood samples collected as part of the prenatal screening in the North Denmark Region, 2011-2015. TSH, fT4, thyroid peroxidase antibodies (TPOAb), and thyroglobulin antibodies (TgAb) were measured using an ADVIA Centaur XPT immunoassay. The reference cohort included 10,337 pregnant women who had no thyroid disease or other autoimmune diseases and were TPOAb- and TgAb negative. The main outcome measures were lower and upper reference limits (2.5th and 97.5th percentiles) for TSH and fT4 stratified by week of pregnancy.

RESULTS

Blood samples were drawn in pregnancy weeks 4-20 (median week 10), and 92% of the pregnancies ended with a live birth. TSH varied considerably in the first trimester of pregnancy, and the levels were highest in early pregnancy (weeks 4-6: 0.6-3.7 mIU/L) followed by a gradual decline to lower levels in weeks 9-11 (0.1-2.8 mIU/L) and 12-14 (0.03-2.8 mIU/L). Maternal fT4 showed less variation (weeks 4-6: 12-20 pmol/L; weeks 9-11: 13-21 pmol/L; weeks 12-14: 13-20 pmol/L).

CONCLUSIONS

The results corroborate dynamic week-specific changes in maternal TSH in early pregnancy. The use of uniform lower and upper reference limits for TSH in early pregnancy may be too simple.

Frequency and outcomes of maternal thyroid function abnormalities in early pregnancy

Thyroid function in pregnant women is of clinical importance considering the crucial role of thyroid hormones during fetal brain development, but the current level of evidence is insufficient to recommend for or against the routine testing of thyroid function in pregnant women. As part of this debate, it is important to evaluate the frequency of undiagnosed and untreated thyroid function abnormalities in pregnant women and to address challenges related to the biochemical assessment of maternal thyroid function in early pregnancy. A hypothesis of fetal programming by maternal thyroid disease has been proposed, but more evidence in humans is needed to extend the hypothesis and to evaluate child neurodevelopmental outcomes after in utero exposure to different abnormalities in maternal thyroid function. The nationwide registers in the Nordic countries provide unique opportunities within reproductive epidemiology to study the impact of various in utero exposures, and stored blood samples from pregnant women in nationwide birth cohorts provide a valuable source for the establishment of pregnancy specific reference ranges. This review addresses the frequency and outcomes of thyroid function abnormalities in pregnant women mainly focusing on observational studies that combine data from the Danish nationwide registers and biological specimens from the Danish National Birth Cohort. Dynamic changes in the reference range of maternal TSH and free T4 during the first trimester of pregnancy are described and discussed. A high frequency of unidentified maternal thyroid function abnormalities is illustrated, and outcomes of child neurodevelopment are evaluated according to subtypes and severity of maternal thyroid dysfunction.

Hypothyroidism during pregnancy and its association to perinatal and obstetric morbidity: a review

There is currently no consensus among the different scientific societies on screening for thyroid dysfunction in the first trimester of pregnancy. Indeed, diagnosis and treatment of subclinical hypothyroidism during pregnancy are controversial, as no cut-off value for thyrotropin (TSH) is universally accepted. TSH measurement may be influenced by different factors throughout pregnancy, but especially during the first trimester. The association between overt hypothyroidism during pregnancy and obstetric and perinatal complications is well established. It is also accepted that thyroid hormones are important for neurodevelopment of the offspring. However, there is no scientific evidence available about the impact of subclinical hypothyroidism and its treatment during the first trimester of pregnancy on children's neurodevelopment. In recent years, studies conducted in the offspring of mothers with subclinical hypothyroidism have reported new biochemical parameters which may eventually serve as biomarkers of offspring neurodevelopment and which are more reproducible and are measured at an earlier time than the conventional clinical tests.

Establishment of trimester-specific reference range for thyroid hormones during pregnancy

OBJECTIVE

Physiological gestational changes are associated with alterations in thyroid function which require different biochemical interpretation from that of non-pregnant women and necessitate established pregnancy-specific reference ranges. We aimed to identify the trimester-specific ranges of thyroid markers in a healthy population of pregnant Iranian women.

METHODS

In this self-sequential study, data were extracted from The Tehran Thyroid and Pregnancy Study; a total of 314 women were tested during the 1st, 2nd and 3rd trimesters for serum levels of thyrotropin (TSH), thyroxine (T4), free thyroxine index (FT4I) and thyroid peroxidase antibody (TPOAb). Trimester-specific reference intervals for TSH, T4 and FT4I and first trimester reference range for TPOAb were estimated. The normal and modulus exponential-normal models were fitted by maximum likelihood using STATA software. The 2.5th and 97.5th percentiles of thyroid parameters were determined and used as reference intervals.

RESULTS

Mean±SD age of participants was 26.8±5.2years. Estimated reference intervals for TSH, T4 and FT4I in the 1st, 2nd and 3rd trimesters corresponding to the 2.5th and 97.5th percentiles were 0.14-6.14, 0.43-4.64, 0.63-3.9μIU/ml; 78.01-215.19, 93.23-243.87, 89.61-211.37nmol/L; and 1.73-4.53, 1.96-5.64, 1.72-4.30, respectively. Reference interval for TPOAb in the 1st trimester was 1.40-38.02IU/mL. Median of TSH was low in the 1st trimester, and gradually increased until 2nd trimester, followed by a slight decrease onward. A decreasing trend in TSH levels was observed in higher centiles with advancing gestational age.

CONCLUSION

This study provides trimester-specific reference ranges for some common thyroid markers among healthy Iranian women in an iodine sufficient area, to prevent biochemical misinterpretations during pregnancy.

Prenatal Diagnosis of Resistance to Thyroid Hormone and Its Clinical Implications

CONTEXT

Resistance to thyroid hormone-β (RTH-β) is an autosomal dominant disorder characterized by reduced sensitivity of target tissues to thyroid hormones (THs). Individuals with RTH-β have high TH levels usually due to mutations in the TH receptor-β (THRB) gene. The management of RTH-β during pregnancy is challenging, as wild-type (WT) fetuses born to RTH-β mothers have low birth weight and suppressed postnatal thyroid-stimulating hormone (TSH), due to intrauterine exposure to excess TH.

OBJECTIVE

To determine birth weight and postnatal TSH of WT fetuses carried by mothers with RTH-β whose fT4 levels were maintained below 20% of the upper limit of normal (ULN).

DESIGN

Retrospective chart review.

SETTING

Academic institution in collaboration with off-site hospitals and private practices.

PATIENTS

Thirteen women harboring THRB gene mutations were evaluated during 18 pregnancies.

INTERVENTION

Prenatal genetic diagnosis by amniocentesis. Women carrying WT fetuses were given the option of treatment with antithyroid medication by their treating physicians with the aim to avoid serum fT4 levels above 20% of the ULN.

RESULTS

No significant difference was found in birth weight corrected for gestational age and in serum TSH levels at birth between WT and RTH-β infants born to RTH-β mothers.

CONCLUSIONS

Prenatal diagnosis may play an important role in the management of RTH-β during pregnancy. Aiming for maternal fT4 levels not above 50% of the ULN in RTH-β mothers carrying WT fetuses seems to be a prudent approach that prevents the otherwise expected low birth weight and postnatal TSH suppression.

Thyroid disease in pregnancy: new insights in diagnosis and clinical management

Adequate thyroid hormone availability is important for an uncomplicated pregnancy and optimal fetal growth and development. Overt thyroid disease is associated with a wide range of adverse obstetric and child development outcomes. An increasing number of studies now indicate that milder forms of thyroid dysfunction are also associated with these adverse pregnancy outcomes. The definitions of both overt and subclinical thyroid dysfunction have changed considerably over the past few years, as new data indicate that the commonly used fixed upper limits of 2.5 mU/l or 3.0 mU/l for thyroid-stimulating hormone (TSH) are too low to define an abnormal thyroid function. Furthermore, some studies now show that the reference ranges are not necessarily the best cut-off for identifying pregnancies at high risk of adverse outcomes. In addition, data suggest that thyroid peroxidase autoantibody positivity and high or low concentrations of human chorionic gonadotropin seem to have a more prominent role in the interpretation of thyroid dysfunction than previously thought. Data on the effects of thyroid disease treatment are lacking, but some studies indicate that clinicians should be aware of the potential for overtreatment with levothyroxine. Here, we put studies from the past decade on reference ranges for TSH, determinants of thyroid dysfunction, risks of adverse outcomes and options for treatment into perspective. In addition, we provide an overview of the current views on thyroid physiology during pregnancy and discuss strategies to identify high-risk individuals who might benefit from levothyroxine treatment.

Increase in thyroglobulin antibody and thyroid peroxidase antibody levels, but not preterm birth-rate, in pregnant Danish women upon iodine fortification

OBJECTIVE

The presence of thyroid antibodies in pregnancy has been associated with preterm birth. In the non-pregnant population, the implementation of the Danish iodine fortification program has increased the prevalence of thyroid antibodies. This study investigated the prevalence of thyroid peroxidase antibodies (TPOAbs) and thyroglobulin antibodies (TgAbs) in pregnant Danish women before, during and after implementation of the iodine fortification program and association with preterm birth.

DESIGN

Comparative cohort study of 1368 pregnancies from three cohorts gathered before (1996-1998), during (2000-2003) and after (2008-2009) the iodine fortification program.

METHODS

In cohort 1 (n = 297), TPOAbs were measured (DYNOtest (BRAHMS)). In cohorts 2 (n = 148) and 3 (n = 923), both TPOAbs and TgAbs were measured (Kryptor immunofluorescent assay (BRAHMS)). The prevalence and effect of antibody positivity were explored using three cut-offs: TPOAbs and/or TgAbs >100 kU/L, TPOAbs and/or TgAbs >60 kU/L and TPOAbs >30 and/or TgAbs >20 kU/L. National preterm birth data were extracted from the National Birth Registry.

RESULTS

In the three cohorts, TPOAb levels >60 kU/L were found in 5.4, 8.1 and 12.0% (χ²(2, n = 1367) = 11.7, P = 0.003) respectively, and TPOAbs and/or TgAbs >60 kU/L in 8.1 and 16.2% in cohorts 2 and 3 respectively (χ²(2, n = 1070) = 6.5, P = 0.01). TgAb levels (>20 kU/L) had increased plenty-fold from cohort 2 to 3 (χ²(1, n = 1071) = 136.5, P < 0.001). Preterm birth occurred in 4.1% of all pregnancies with no effect from antibody positivity (TPOAbs and/or TgAbs >60 kU/L, χ²(1, n = 1039) = 0.0, P = 0.98, aOR = 1.1, 95% CI (0.4-2.7)). The national preterm birth-rate showed no increase over the same period.

CONCLUSIONS

Thyroid antibody positivity in Danish pregnant women has more than doubled upon the implementation of the iodine fortification program without an increase in preterm birth-rate.

Patients with subclinical hypothyroidism before 20 weeks of pregnancy have a higher risk of miscarriage: A systematic review and meta-analysis

Objective

To evaluate the relationship between subclinical hypothyroidism (SCH) and the risk of miscarriage before 20 weeks of pregnancy.

Methods

Literature databases were searched, including the PubMed, Web of Science, Embase and Cochrane databases, from January 1, 1980, to December 31, 2015. The following search terms were used: subclinical hypothyroidism, hypothyroidism, thyroid dysfunction, thyroid hypofunction, subclinical thyroid disease, thyroid dysfunction, pregnancy loss, abortion and miscarriage. Studies comparing the prevalence of miscarriage in pregnant women with SCH with those who were euthyroid were selected. From the studies matched, the relative risk (RR) and corresponding 95% confidence interval (95% CI) were calculated to yield outcomes. All the statistical analyses were performed using Review Manager (Revman) Version 5.3 and Stata Version 12.0 software. The publication bias of the studies was assessed by forest plot and Begg’s test, while the stability of the results was evaluated by sensitivity analysis.

Results

Nine articles satisfying the inclusion criteria were analysed. Compared to euthyroid pregnant women, patients with non-treated SCH had a higher prevalence of miscarriage (RR = 1.90, 95% CI1.59–2.27, P<0.01). Additionally, SCH patients in the international diagnostic criteria group were more likely to suffer miscarriages than those in the ATA diagnostic criteria group (χ² = 11.493, P<0.01). Moreover, there was no difference between patients with treated SCH and euthyroid women (RR = 1.14, 95% CI0.82–1.58, P = 0.43). Compared to isolated SCH women, the miscarriage risk of SCH patients with thyroid autoimmunity (TAI) was obviously higher (RR = 2.47, 95% CI1.77–3.45, P<0.01), and isolated SCH patients also had a higher prevalence of miscarriages than euthyroid women (RR = 1.45, 95% CI1.07–1.96, P = 0.02).A heterogeneity test, forest plot and Begg’s test suggested that there was no significant heterogeneity or publication bias among the included articles, while the result of sensitivity analysis showed that our study exhibited high stability.

Conclusion

SCH is a risk factor for miscarriage in women before 20 weeks of pregnancy, and early treatments can reduce the miscarriage rate. Regardless of the diagnostic criteria used, the miscarriage rate increased as long as a pregnant woman was confirmed to have SCH. The results show that the omission diagnostic rate may increase when the ATA diagnostic criteria are used. In addition, SCH patients with TAI have a higher prevalence of miscarriage, while isolated SCH patients also have a higher miscarriage rate than euthyroid women. Thus, we recommend early treatments to avoid adverse pregnancy outcomes and complications.

Reference Values for TSH and Free Thyroid Hormones in Healthy Pregnant Women in Poland: A Prospective, Multicenter Study

OBJECTIVES

The diagnosis and treatment of thyroid diseases in pregnant women remains a challenge. Various medical associations recommend establishing the reference intervals for thyroid hormones by a local laboratory. Considering differences within geophysical, socioeconomic conditions, and iodine prophylaxis in various populations, it is advisable to assess reference intervals for thyroid hormones specific to a region of residence. The objective was to assess trimester-specific reference intervals for TSH, fT₃, and fT₄ for pregnant women in the Polish population.

METHODS AND RESULTS

We conducted a prospective study in 4 centers representing different regions of Poland (Krakow, Warsaw, Poznan, and Bialystok). Our study included consecutive, healthy pregnant women (172 patients), with an age range of 27-47 years. All women had a negative history for thyroid diseases, normal thyroid peroxidase antibody levels, and proper iodine prophylaxis. All newborns had TSH levels in the appropriate reference range. Serum TSH, fT₃, fT₄, and thyroid-peroxidase antibodies were measured in each trimester. The reference intervals were calculated using the percentile method, as recommended by the International Federation of Clinical Chemistry. The reference values calculated were 0.009-3.177, 0.05-3.442, and 0.11-3.53 mIU/L for TSH; 3.63-6.55, 3.29-5.45, and 3.1-5.37 pmol/L for fT₃; and 11.99-21.89, 10.46-16.67, and 8.96-17.23 pmol/L for fT₄ in consecutive trimesters of pregnancy. Reference intervals for pregnant women when compared to the general population showed a lower concentration of TSH in every trimester of pregnancy and lower fT₄ in the 2nd and 3rd trimesters.

CONCLUSIONS

Using appropriate trimester-specific reference intervals may improve care of pregnant women by preventing misdiagnosis and inadequate treatment.

Comparison of the Reference Intervals Used for the Evaluation of Maternal Thyroid Function During Pregnancy Using Sequential and Nonsequential Methods

BACKGROUND

Maternal thyroid dysfunction is common during pregnancy, and physiological changes during pregnancy can lead to the overdiagnosis of hyperthyroidism and misdiagnosis of hypothyroidism with nongestation-specific reference intervals. Our aim was to compare sequential with nonsequential methods for the evaluation of thyroid function in pregnant women.

METHODS

We tested pregnant women who underwent their trimester prenatal screening at our hospital from February 2011 to September 2012 for serum thyroid stimulating hormone (TSH) and free thyroxine (FT4) using the Abbott and Roche kits. There were 447 and 200 patients enrolled in the nonsequential and sequential groups, respectively. The central 95% range between the 2.5th and the 97.5th percentiles was used as the reference interval for the thyroid function parameter.

RESULTS

The nonsequential group exhibited a significantly larger degree of dispersion in the TSH reference interval during the 2nd and 3rd trimesters as measured using both the Abbott and Roche kits (all P < 0.05). The TSH reference intervals were significantly larger in the nonsequential group than in the sequential group during the 3rd trimester as measured with both the Abbott (4.95 vs. 3.77 mU/L, P < 0.001) and Roche kits (6.62 vs. 5.01 mU/L, P = 0.004). The nonsequential group had a significantly larger FT4 reference interval as measured with the Abbott kit during all trimesters (12.64 vs. 5.82 pmol/L; 7.96 vs. 4.77 pmol/L; 8.10 vs. 4.77 pmol/L, respectively, all P < 0.05), whereas a significantly larger FT4 reference interval was only observed during the 2nd trimester with the Roche kit (7.76 vs. 5.52 pmol/L, P = 0.002).

CONCLUSIONS

It was more reasonable to establish reference intervals for the evaluation of maternal thyroid function using the sequential method during each trimester of pregnancy. Moreover, the exclusion of pregnancy-related complications should be considered in the inclusion criteria for thyroid function tests.

ENDOCRINOLOGY IN PREGNANCY: Pregnancy and the incidence, diagnosing and therapy of Graves' disease

Thyroid hormones are essential developmental factors, and Graves' disease (GD) may severely complicate a pregnancy. This review describes how pregnancy changes the risk of developing GD, how early pregnancy by several mechanisms leads to considerable changes in the results of the thyroid function tests used to diagnose hyperthyroidism, and how these changes may complicate the diagnosing of GD. Standard therapy of GD in pregnancy is anti-thyroid drugs. However, new studies have shown considerable risk of birth defects if these drugs are used in specific weeks of early pregnancy, and this should be taken into consideration when planning therapy and control of women who may in the future become pregnant. Early pregnancy is a period of major focus in GD, where pregnancy should be diagnosed as soon as possible, and where important and instant change in therapy may be warranted. Such change may be an immediate stop of anti-thyroid drug therapy in patients with a low risk of rapid relapse of hyperthyroidism, or it may be an immediate shift from methimazole/carbimazole (with risk of severe birth defects) to propylthiouracil (with less risk), or maybe to other types of therapy where no risk of birth defects have been observed. In the second half of pregnancy, an important concern is that not only the mother with GD but also her foetus should have normal thyroid function.

Managing hyperthyroidism in pregnancy: current perspectives

Hyperthyroidism in women who are of childbearing age is predominantly of autoimmune origin and caused by Graves' disease. The physiological changes in the maternal immune system during a pregnancy may influence the development of this and other autoimmune diseases. Furthermore, pregnancy-associated physiological changes influence the synthesis and metabolism of thyroid hormones and challenge the interpretation of thyroid function tests in pregnancy. Thyroid hormones are crucial regulators of early development and play an important role in the maintenance of a normal pregnancy and in the development of the fetus, particularly the fetal brain. Untreated or inadequately treated hyperthyroidism is associated with pregnancy complications and may even program the fetus to long-term development of disease. Thus, hyperthyroidism in pregnant women should be carefully managed and controlled, and proper management involves different medical specialties. The treatment of choice in pregnancy is antithyroid drugs (ATDs). These drugs are effective in the control of maternal hyperthyroidism, but they all cross the placenta, and so need careful management and control during the second half of pregnancy considering the risk of fetal hyper- or hypothyroidism. An important aspect in the early pregnancy is that the predominant side effect to the use of ATDs in weeks 6-10 of pregnancy is birth defects that may develop after exposure to available types of ATDs and may be severe. This review focuses on four current perspectives in the management of overt hyperthyroidism in pregnancy, including the etiology and incidence of the disease, how the diagnosis is made, the consequences of untreated or inadequately treated disease, and finally how to treat overt hyperthyroidism in pregnancy.

Impact of thyroid autoimmunity on cumulative delivery rates in in vitro fertilization/intracytoplasmic sperm injection patients

OBJECTIVE

To predict the impact of thyroid autoimmunity (TAI) on the probability of delivery after a defined number of treatment cycles, using analysis of cumulative delivery rates in patients with and without TAI.

DESIGN

Retrospective cohort study performed at the Center for Reproductive Medicine and Department of Endocrinology, University Hospital of Brussels, approved by the institutional review board of the hospital.

SETTING

University hospital.

PATIENT(S)

All patients who started their first IVF/intracytoplasmic sperm injection cycle at our fertility center between January 1, 2010 and December 31, 2011 were included.

MAIN OUTCOME MEASURE(S)

Live birth delivery after 25 weeks' gestation was taken as the primary endpoint of our study Cumulative delivery rates were calculated for both groups until six treatment cycles.

INTERVENTION(S)

All patients (in both groups) received the usual IVF treatment protocols (i.e., antagonist or agonist protocol).

RESULT(S)

In total 2,406 women who consulted our center were included. We included 333 patients with TAI and 2019 patients without TAI. In the TAI group the crude cumulative delivery rate after six cycles was 47%, whereas the expected cumulative delivery rate was 65%. In our control the crude cumulative delivery rate after six cycles was 47%, whereas the expected cumulative delivery rate was 76%.

CONCLUSION(S)

Our study did not confirm an influence of TAI status in patients undergoing fertility treatment on cumulative delivery rates after six IVF/intracytoplasmic sperm injection cycles.

Thyroid function and autoimmunity in Danish pregnant women after an iodine fortification program and associations with obstetric outcomes

OBJECTIVE

Aberrations in maternal thyroid function and autoimmunity during pregnancy have been associated with negative obstetric outcome. In Denmark, a national iodine fortification program was implemented in the year 2000 with the aim to alleviate the mild-moderate iodine deficiency. Following the iodine implementation, there has been an increase in thyroid autoimmunity in the background population. This study investigates the thyroid status of pregnant Danish women following the iodine fortification program, and a possible association with preterm delivery.

DESIGN

Historical cohort study of 1278 randomly selected pregnant Danish women attending the national Down's syndrome screening program.

METHODS

The main outcome measures were thyroid status according to laboratory- and gestational-age-specific reference intervals, and association with risk of abnormal obstetric outcome. Antibody-positivity was defined as an antibody-level (thyroid peroxidase and/or thyroglobulin antibodies) above 60 U/ml.

RESULTS

Establishing laboratory-specific gestational-age-dependent reference intervals, we found a prevalence of maternal thyroid dysfunction of 10%-15.8% by use of the cut-off suggested by the American Thyroid Association. Thyroid dysfunction was significantly associated with antibody-positivity (P<0.05). No associations were found between preterm delivery and thyroid dysfunction (adjusted OR 0.6, 95% CI: 0.1-2.3) or autoimmunity (adjusted OR 1.1, 95% CI: 0.4-2.7).

CONCLUSIONS

After the implementation of the Danish iodine fortification program, the prevalence of thyroid dysfunction and autoimmunity in Danish pregnant women is high - even higher by use of pre-established reference intervals from international consensus guidelines. However, no associations were found with abnormal obstetric outcome. Large randomized controlled trials are needed to clarify the benefit of treating slight aberrations in pregnant women's thyroid function.

Pregnancy outcomes and relationship to treatment adequacy in women treated early for congenital hypothyroidism: a longitudinal population-based study

CONTEXT

Untreated hypothyroidism is associated with a higher risk of adverse obstetric and neonatal outcomes. Pregnancy complications have yet to be evaluated in patients treated early for congenital hypothyroidism (CH).

OBJECTIVE

This study aimed to investigate pregnancy outcomes and their determinants in a population-based registry of young adult women with CH.

SETTING AND DESIGN

In total, 1748 subjects were diagnosed with CH in the first 10 years after the introduction of neonatal screening in France; 1158 of these subjects completed a questionnaire on fecundity at a mean age of 25.3 years. We analyzed all declared singleton pregnancies ending after greater than 22 weeks of gestation before the initial survey (n = 207 pregnancies) and in the 3 years following the initial survey (prospective study, n = 174 pregnancies). The reference group comprised 7245 subjects from the French National Perinatal Survey.

MAIN OUTCOME MEASURES

Pregnancy outcomes. Serum TSH concentrations and thyroid hormone requirements.

RESULTS

In both the overall and prospective analyses, CH was associated with gestational hypertension, emergency cesarean delivery, induced labor for vaginal delivery, and prematurity. For the prospective population with CH, the adjusted odds ratios (aOR) (95% confidence interval [CI]) were 2.19 (1.26-3.81), 1.88 (1.17-3.02), 1.58 (1.12-2.24), and 1.85 (1.06-3.25), respectively. TSH concentrations at least 10 mIU/l during the first 3 or 6 months of pregnancy were associated with a higher risk of preterm delivery (aOR, 5.6; 95% CI, 1.6-20.0) and fetal macrosomia (aOR, 4.5; 95% CI, 1.03-20.1), respectively, whereas no such relationship was observed for TSH concentrations of 5.0-9.9 mIU/l.

CONCLUSION

CH may result in adverse pregnancy outcomes. These nationwide data suggest that better thyroid disease management is required, particularly during the first two trimesters of pregnancy, together with vigilant monitoring.

Update on a new controversy in endocrinology: isolated maternal hypothyroxinemia

Isolated hypothyroxinemia (IH) is defined as a thyroxine level in the lower 5th (severe IH) or 10th percentile (mild IH) of the pregnancy-related reference range and a normal TSH. The etiology of IH remains unknown. This review aims to evaluate the biochemical criteria used to define IH in different published studies and to discuss potential maternal as well as fetal outcomes and whether treatment during early pregnancy can prevent the eventual adverse effects. For the current literature a better standardization of free thyroxine assays is needed, as well as the use of appropriated trimester-specific reference intervals for thyroid function tests. Today no study demonstrates a benefit from treating early pregnant IH women on perinatal and fetal outcomes.

Thyrotoxicosis of Pregnancy

Thyrotoxicosis presenting during pregnancy is a common clinical problem and can be challenging to differentiate between physiologic patterns of thyroid dysfunction during gestation and intrinsic hyperthyroidism. This review provides a summary of the differential diagnosis, clinical presentation, diagnostic options, potential adverse effects of maternal thyrotoxicosis to the fetus, and treatment recommendations for thyrotoxicosis arising in pregnancy.

Conservative management of pregnancy in patients with resistance to thyroid hormone associated with Hashimoto's thyroiditis

BACKGROUND

Resistance to thyroid hormone (RTH) is a rare thyroid disorder characterized by elevated free thyroid hormones with non-suppressed thyrotropin (TSH). Guidelines for the management of pregnancy in patients with RTH are not well defined. Chorionic villus biopsy is sometimes proposed to manage treatment based on the genotype of the fetus.

PATIENT FINDINGS

A woman with RTH (c1243C>T, pR320C mutation in the thyroid hormone receptor β (THRB gene)) associated with Hashimoto's thyroiditis (HT) had three successful pregnancies. During the pregnancies, the mother was treated with levothyroxine (LT4). She never underwent chorionic villus sampling. The babies had normal birth weights. The first child harbored the THRB mutation.

SUMMARY AND CONCLUSIONS

The management of pregnancies in patients with RTH and the indication for chorionic villus sampling are discussed in these cases. In RTH patients, pregnancies must be planned and closely followed. There is no need for prenatal diagnosis of RTH if the patient, due to limited thyroidal reserve, cannot produce excess of thyroid hormones to harm a normal fetus. The more common challenge in RTH remains how to best manage high maternal thyroid hormone levels, and whether or not to lower thyroid hormone levels based on the genotype of the fetus.