Maternal total T4 during the first half of pregnancy: physiologic aspects and the risk of adverse outcomes in comparison with free T4

Physiological Changes in Pregnant Women Due to Hormonal Changes

Pregnancy affects many organ systems and causes significant physiological changes that are mainly caused by changes in hormone levels. This review explores the complex interactions between pregnancy-related hormonal changes and renal function, providing insights into the practical applications of these relationships. Extensive literature searches were conducted, combining data from several sources to produce thorough knowledge. Essential discoveries include changes in renal hemodynamics, calcium/phosphorus level variations, thyroid gland hypertrophy, changed function, and cardiovascular adaptations. The review also addresses how sex hormones affect immunological responses, emphasizing their importance for conditions like multiple sclerosis. Additionally impacted is the gastrointestinal tract, which results in symptoms like nausea and heartburn. Comprehending these physiological changes is essential for proficient therapeutic handling, guaranteeing the best possible health for both the mother and the fetus. The study emphasizes the importance of specialized medical treatment during pregnancy and calls for more investigation to clarify the intricacies of these physiological changes.

Association of Gestational Free and Total Triiodothyronine With Gestational Hypertension, Preeclampsia, Preterm Birth, and Birth Weight: An Individual Participant Data Meta-analysis

CONTEXT

Triiodothyronine (T3) is the bioactive form of thyroid hormone. In contrast to thyroid-stimulating hormone and free thyroxine, we lack knowledge on the association of gestational T3 with adverse obstetric outcomes.

OBJECTIVE

To investigate the associaiton of gestational free or total T3 (FT3 or TT3) with adverse obstetric outcomes.

METHODS

We collected individual participant data from prospective cohort studies on gestational FT3 or TT3, adverse obstetric outcomes (preeclampsia, gestational hypertension, preterm birth and very preterm birth, small for gestational age [SGA], and large for gestational age [LGA]), and potential confounders. We used mixed-effects regression models adjusting for potential confounders.

RESULTS

The final study population comprised 33 118 mother-child pairs of which 27 331 had data on FT3 and 16 164 on TT3. There was a U-shaped association of FT3 with preeclampsia (P = .0069) and a J-shaped association with the risk of gestational hypertension (P = .029). Higher TT3 was associated with a higher risk of gestational hypertension (OR per SD of TT3 1.20, 95% CI 1.08 to 1.33; P = .0007). A lower TT3 but not FT3 was associated with a higher risk of very preterm birth (OR 0.72, 95% CI 0.55 to 0.94; P = .018). TT3 but not FT3 was positively associated with birth weight (mean difference per 1 SD increase in TT3 12.8, 95% CI 6.5 to 19.1 g, P < .0001) but there was no association with SGA or LGA.

CONCLUSION

This study provides new insights on the association of gestational FT3 and TT3 with major adverse pregnancy outcomes that form the basis for future studies required to elucidate the effects of thyroid function on pregnancy outcomes. Based on the current study, routine FT3 or TT3 measurements for the assessment of thyroid function during pregnancy do not seem to be of added value in the risk assessment for adverse outcomes.

Associations of urinary non-persistent endocrine disrupting chemical biomarkers with early-to-mid pregnancy plasma sex-steroid and thyroid hormones

BACKGROUND/OBJECTIVES

Pregnant women are exposed to numerous endocrine disrupting chemicals (EDCs) that can affect hormonal pathways regulating pregnancy outcomes and fetal development. Thus, we evaluated overall and fetal sex-specific associations of phthalate/replacement, paraben, and phenol biomarkers with sex-steroid and thyroid hormones.

METHODS

Illinois women (n = 302) provided plasma for progesterone, estradiol, testosterone, free T4 (FT4), total T4 (TT4), and thyroid stimulating hormone (TSH) at median 17 weeks gestation. Women also provided up-to-five first-morning urine samples monthly across pregnancy (8-40 weeks), which we pooled to measure 19 phthalate/replacement metabolites (reflecting ten parent compounds), three parabens, and six phenols. We used linear regression to evaluate overall and fetal sex-specific associations of biomarkers with hormones, as well as weighted quantile sum and Bayesian kernel machine regression (BKMR) to assess cumulative associations, non-linearities, and chemical interactions.

RESULTS

In women of relatively high socioeconomic status, several EDC biomarkers were associated with select hormones, without cumulative or non-linear associations with progesterone, FT4, or TT4. The biomarker mixture was negatively associated with estradiol (only at higher biomarker concentrations using BKMR), testosterone, and TSH, where each 10% mixture increase was associated with -5.65% (95% CI: -9.79, -1.28) lower testosterone and -0.09 μIU/mL (95% CI: -0.20, 0.00) lower TSH. Associations with progesterone, testosterone, and FT4 did not differ by fetal sex. However, in women carrying females, we identified an inverted u-shaped relationship of the mixture with estradiol. Additionally, in women carrying females, each 10% increase in the mixture was associated with 1.50% (95% CI: -0.15, 3.18) higher TT4, whereas in women carrying males, the mixture was associated with -1.77% (95% CI: -4.08, 0.58) lower TT4 and -0.18 μIU/mL (95% CI: -0.33, -0.03) lower TSH. We also identified select chemical interactions.

CONCLUSION

Some biomarkers were associated with early-to-mid pregnancy hormones. There were some sex-specific and non-linear associations. Future studies could consider how these findings relate to pregnancy/birth outcomes.

Physiologic Changes During Pregnancy and Impact on Small-Molecule Drugs, Biologic (Monoclonal Antibody) Disposition, and Response

Pregnancy is a unique physiological state that results in many changes in bodily function, including cellular, metabolic, and hormonal changes. These changes can have a significant impact on the way small-molecule drugs and monoclonal antibodies (biologics) function and are metabolized, including efficacy, safety, potency, and adverse effects. In this article, we review the various physiologic changes that occur during pregnancy and their effects on drug and biologic metabolism, including changes in the coagulation, gastrointestinal, renal, endocrine, hepatic, respiratory, and cardiovascular systems. Additionally, we discuss how these changes can affect the processes of drug and biologic absorption, distribution, metabolism, and elimination (pharmacokinetics), and how drugs and biologics interact with biological systems, including mechanisms of drug action and effect (pharmacodynamics) during pregnancy, as well as the potential for drug-induced toxicity and adverse effects in the mother and developing fetus. The article also examines the implications of these changes for the use of drugs and biologics during pregnancy, including consequences of suboptimal plasma drug concentrations, effect of pregnancy on the pharmacokinetics and pharmacodynamics of biologics, and the need for careful monitoring and individualized drug dosing. Overall, this article aims to provide a comprehensive understanding of the physiologic changes during pregnancy and their effects on drug and biologic metabolism to improve the safe and effective use of drugs.

Evaluating thyroid function in pregnant women

Thyroid hormones are primarily responsible for regulating the basal metabolic rate but also make important contributions to reproductive function and fetal development. Both hyper- and hypothyroidism in pregnancy have been associated with increased risks of complications that include preeclampsia and low birth weight, among others. Furthermore, thyroid hormone deficiency in the developing fetus results in neurodevelopmental delay. As the fetus is exclusively reliant on maternal thyroid hormone for most of the first trimester and requires continued maternal supply until birth, identifying maternal thyroid dysfunction is critically important. However, evaluating thyroid function in pregnancy is challenging because of the many physiological changes that affect concentrations of thyroid-related analytes. Increasing plasma human chorionic gonadotropin (hCG) concentrations in the second half of the first trimester elicit a corresponding transient decrease in thyroid-stimulating hormone (TSH), and continually increasing estradiol concentrations throughout pregnancy cause substantial increases in thyroxine-binding globulin (TBG) and total thyroxine (T4) relative to the nonpregnant state. Lastly, free T4 concentrations gradually decrease with increasing gestational age. For these reasons, it is essential to interpret thyroid function test results in the context of trimester-specific reference intervals to avoid misclassification of thyroid status. This review summarizes the effects of thyroid dysfunction prior to conception and during pregnancy and describes considerations for the laboratory assessment of thyroid function in pregnant women.

Association of thyroid dysfunction and autoantibody positivity with the risk of preterm birth: a hospital-based cohort study

BACKGROUND

Evidence for the association of thyroid dysfunction and autoantibody positivity with preterm birth remains controversial. We aimed to study the association of maternal thyroid dysfunction and autoantibody positivity with the risk of preterm birth.

METHOD

A hospital-based cohort study of 40,214 women was conducted. Gestational age-specific percentiles of the FT4 and TSH concentrations were used for the definition of thyroid dysfunction. Autoantibody positivity was identified when the concentration > the threshold. The association of thyroid dysfunction and autoantibody positivity with the risk of preterm birth was estimated.

RESULTS

No significant higher risk of preterm birth was found for women with variants of thyroid dysfunction or autoantibody positive than euthyroid women. Sensitivity and stratification analyses indicated that thyroperoxidase antibody (TPOAb) positivity in the first trimester (odds ratio [OR], 1.49; 95% confidence interval [CI], 1.17-1.90) and overt hypothyroidism restricted to women negative for TPOAb (OR, 4.94; 95%CI: 1.64-14.84) was associated with an increased risk of preterm birth. Modification effects of gestational age were found for women who had the test ≤18 and > 18 weeks. Continuous FT4 measurements tested ≤18 weeks of gestation were associated with a higher risk of preterm birth (OR, 1.13, 95% CI: 1.00-1.28), while a negative relationship for FT4 concentrations tested > 18 weeks of gestation (OR = 0.68, 95% CI: 0.48-0.97).

CONCLUSIONS

Some specific thyroid function abnormalities were associated with an increased risk of preterm birth. Interaction between gestational age and FT4 concentration on the risk of preterm birth was identified, with a critical node of 18 weeks of gestation.

Biomarkers of Exposure to Phthalate Mixtures and Adverse Birth Outcomes in a Puerto Rico Birth Cohort

BACKGROUND

Humans are exposed to complex mixtures of phthalate chemicals from a range of consumer products. Previous studies have reported significant associations between individual phthalate metabolites and pregnancy outcomes, but mixtures research is limited.

OBJECTIVES

We used the Puerto Rico Testsite for Exploring Contamination Threats longitudinal pregnancy cohort to investigate associations between phthalate metabolite mixtures and pregnancy outcomes.

METHODS

Women (n=462 carrying females, n=540 carrying males) provided up to three urine samples throughout gestation (median 18, 22, and 26 wk), which were analyzed for 13 phthalate metabolites. Pregnancy outcomes including preterm birth (PTB), spontaneous PTB, small and large for gestational age (SGA, LGA), birth weight z-score, and gestational age at delivery were abstracted from medical records. Environmental risk scores (ERS) were calculated as a weighted linear combination of the phthalates from ridge regression and adaptive elastic net, which are variable selection methods to handle correlated predictors. Birth outcomes were regressed on continuous ERS. We assessed gestational average and visit-specific ERS and stratified all analyses by fetal sex. Finally, we used Bayesian kernel machine regression (BKMR) to explore nonlinear associations and interactions between metabolites.

RESULTS

Differences in metabolite weights from ridge and elastic net were apparent between birth outcomes and between fetal sexes. An interquartile range increase in gestational average phthalate ERS was associated with increased odds of PTB [male odds ratio (OR)=1.56; 95% confidence interval (CI): 1.08, 2.27; female OR=1.91; 95% CI: 1.23, 2.98], spontaneous PTB (male OR=2.32; 95% CI: 1.46, 3.68; female OR=2.00; 95% CI: 1.04, 3.82), and reduced gestational age at birth (male β=-0.39 wk, 95% CI: -0.62, -0.15; female β=-0.29 wk, 95% CI: -0.52, -0.05). Analyses by study visit suggested that exposure at ∼22 wk (range 20-24 wk) was driving those associations. Bivariate plots from BKMR analysis revealed some nonlinear associations and metabolite interactions that were different between fetal sexes.

DISCUSSION

These results suggest that exposure to phthalate mixtures was associated with increased risk of early delivery and highlight the need to study mixtures by fetal sex. We also identified various metabolites displaying nonlinear relationships with measures of birth weight. https://doi.org/10.1289/EHP8990.

Association between Maternal Thyroxine and Risk of Fetal Congenital Heart Defects: A Hospital-Based Cohort Study

BACKGROUND

Evidence for the association between maternal thyroxine concentration and the risk of fetal congenital heart defects (CHDs) is absent. We aimed to study the association of maternal free and total thyroxine (FT4 and TT4) concentrations and the free-to-total thyroxine proportion (FTT4P, %) with the risk of CHD.

METHODS

The study was a hospital-based cohort study of 52,047 women who received a universal thyroid function test between 2012 and 2016. CHD was screened by ultrasound between 20 and 24 weeks of gestation or diagnosed until the 42^nd day of birth. Adjusted odds ratios (ORs) of fetal CHD were estimated for maternal FT4 and TT4 concentrations or the FTT4P by multivariate logistic regression.

RESULTS

A total of 41,647 women with singleton pregnancies were included for the analysis and 215 CHD cases were detected. The FT4 concentration was significantly associated with a higher risk of CHDs (OR, 1.04, 95% confidence interval (CI): 1.01 to 1.07). Each 1% higher FTT4P was related to a 1.41-fold (95% CI: 0.27 to 3.59) higher risk of CHDs. The association became stronger for women with a thyroid function test performed between 12 and 18 weeks of gestation (OR = 1.05 (95% CI: 1.01 to 1.09) for the FT4 concentration and 3.32 (95% CI: 1.43 to 7.73) for the FTT4P).

CONCLUSIONS

A higher FT4 concentration or FTT4P, measured between 12 and 18 weeks of gestation, was associated with an increased risk of CHDs. These findings may provide new insights into the mechanisms of CHDs and evidence for clinical decisions related to thyroid function tests.

Physiological changes in pregnancy and their influence on the endocrine investigation

BACKGROUND

Physiological changes in pregnancy may result in significant alterations in endocrine hormone profiles, serum and urine electrolytes and endocrine gland morphology on imaging. Pregnancy-specific pathophysiological processes may also affect the results for endocrine tests. Investigation of endocrine disorders in pregnancy requires knowledge of these changes and awareness of the safety of dynamic hormone testing and imaging for the mother and foetus.

OBJECTIVE

This review seeks to outline the important physiological changes in pregnancy affecting reference intervals of basal and dynamic endocrine tests in pregnancy and the scenarios in which these changes are clinically significant, the pregnancy-specific disorders that may affect the investigation of endocrine disorders, and the safety of dynamic testing and imaging.

CONCLUSION

Awareness of the effect of physiological changes, and the potential impact of pregnancy-specific disorders of endocrine tests, and the safety of imaging is crucial to the management of endocrine disorders in pregnancy.

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.

Gestational Hormone Concentrations Are Associated With Timing of Delivery in a Fetal Sex-Dependent Manner

BACKGROUND

Early delivery remains a significant public health problem that has long-lasting impacts on mother and child. Understanding biological mechanisms underlying timing of labor, including endocrine disruption, can inform prevention efforts.

METHODS

Gestational hormones were measured among 976 women in PROTECT, a longitudinal birth cohort in Puerto Rico. We evaluated associations between hormone concentrations at 18 and 26 weeks gestation and gestational age at birth, while assessing effect modification by fetal sex. Exploratory analyses assessed binary outcomes of overall preterm birth (PTB, <37 weeks gestation) and the spontaneous PTB subtype, defined as preterm premature rupture of membranes, spontaneous preterm labor, or both. Multivariable logistic and linear regressions were fit using visit-specific hormone concentrations, and fetal sex-specific effects were estimated using interaction terms. Main outcome models were adjusted for maternal age, education, marital status, alcohol consumption, environmental tobacco smoke exposure, and pre-pregnancy body mass index (BMI). Exploratory models adjusted for maternal age and education.

RESULTS

We observed reduced gestational age at birth with higher circulating CRH (β: -2.73 days, 95% CI: -4.97, -0.42), progesterone (β: -4.90 days, 95% CI: -7.07, -2.73), and fT4 concentrations (β: -2.73 days, 95% CI: -4.76, -0.70) at 18 weeks specifically among male fetuses. Greater odds of overall and spontaneous PTB were observed among males with higher CRH, estriol, progesterone, total triiodothyronine (T3), and free thyroxine (fT4) concentrations. Greater odds of PTB among females was observed with higher testosterone concentrations.

CONCLUSIONS

Various associations between hormones and timing of delivery were modified by fetal sex and timing of hormone measurement. Future studies are needed to understand differential mechanisms involved with timing of labor between fetal sexes.

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.

Total T4 rise in pregnancy: a relook?

Background

Total T4 (TT4) measurement is preferred to free T4 (FT4) especially in last part of pregnancy. Guidelines by American Thyroid Association, European Thyroid Association and Endocrine Society state that TT4 increases 1.5 times pre-pregnant levels after week 16 of pregnancy. However, this is based on a small study conducted 40 years ago which used radioimmunoassay for determination in changes in TT4.

Materials and methods

A cross-sectional study was undertaken to find reference interval for thyroid function in different trimester of pregnancy with special reference to look at the degree of elevation of TT4 as compared to non-pregnant women. Two hundred non-pregnant women (excluding oral contraceptive users) and 600 pregnant women (200 from each trimester) aged 18–40 years were consecutively recruited starting from around 6th week of pregnancy having confirmed singleton pregnancy diagnosed at 8th week by ultrasound. The exclusion criteria included: (1) a personal or family history of thyroid disease; (2) presence of goiter or nodule confirmed by ultrasound; (3) anti-TPO antibody positive state (titre > 35 IU/ml). All subjects were tested for urinary spot iodine concentration and those with UIC < 150 μg/L were excluded. Finally, thyroid function tests (TSH, FT4, TT4, TT3) of 168 non-pregnant women and 163, 153 and 148 women at 1st, 2nd and 3rd trimester respectively were analysed..

Results

Total T4 (mean ± SD, μg/dl) in non pregnant women and in different trimesters was 8.95 ± 1.71, 9.71 ± 2.39, 12.11 ± 1.55, 11.83 ± 1.49 respectively. Rise in TT4 occurred between 10-18th week. The mean TT4 in second trimester increased by 25% as compared with the value at 6-9th week and by 35% as compared to non-pregnant value.

Conclusion

Rise in total T4 in second trimester pregnancy is only around 25% as compared to first trimester value and 35% than the non-pregnant value. Hence multiplying non-pregnant T4 value by 1.5 may actually over-diagnose maternal hypothroxinemia and lead to inappropriate diagnosis and treatment of isolated maternal hypothyroxinemia in a significant proportion of subjects.

Interpretation of thyroid function tests during pregnancy

Thyroid hormones are crucial for normal pregnancy and fetal development. Large physiological changes occur during pregnancy, posing challenges for the correct interpretation of thyroid function tests. TSH concentrations are the principal first test to rule out thyroid disease taking into account trimester-specific reference ranges. Free T4 (FT4) measurements by immuno-assays may be subject to interference by endogenous and exogenous factors. The relevance of measuring free T3 (FT3) during pregnancy is unclear. Thyroid autoimmunity is well-reflected by the presence of antibodies against TPO. TPO-antibody positivity is associated with an increased risk of adverse pregnancy outcomes.

The impact of isolated maternal hypothyroxinemia during the first and second trimester of gestation on pregnancy outcomes: an intervention and prospective cohort study in China

OBJECTIVES

To explore the effect of isolated maternal hypothyroxinemia (IMH) during the first and second trimester of gestation on pregnancy outcomes. To explore whether levothyroxine (L-T4) treatment of women who had IMH identified in the first trimester improves pregnancy outcomes.

METHODS

Women in the early pregnancy in the iodine-sufficient area (n = 3398) were recruited to this prospective cohort study (ChiCTR-TRC-12002326). Serum thyroid-stimulating hormone (TSH), free thyroxine (FT4), and thyroid peroxidase antibody (TPOAb) were detected. Women with IMH before 12 weeks chose to receive L-T4 or remain untreated. The L-T4 dose was adjusted to attain a normal FT4 and TSH level. Pregnancy outcomes were evaluated during follow-up.

RESULTS

IMH in the first trimester was not associated with increased risk of adverse pregnancy outcome compared with controls. The incidence of macrosomia (p = 0.022) and gestational hypertension (p = 0.018) was significantly higher in IMH identified in the second trimester of gestation compared with controls. IMH identified in the second trimester of gestation was a risk factor for macrosomia [adjusted odds ratio (aOR) 1.942, 95% CI 1.076-3.503, p = 0.027] and gestational hypertension (aOR 4.203, 95% CI 1.611-10.968, p < 0.01), when body mass index in the early pregnancy was < 25 kg/m².

CONCLUSIONS

IMH in the first trimester did not increase the risk of adverse outcomes irrespective of whether women received L-T4 treatment. However, IMH identified in the second trimester was associated with increased risk of adverse pregnancy outcome. The results suggest that thyroid function follow-up during the second trimester is necessary, even if thyroid function is normal during the first trimester.

Recent recommendations from ATA guidelines to define the upper reference range for serum TSH in the first trimester match reference ranges for pregnant women in Rio de Janeiro

OBJECTIVES

American Thyroid Association (ATA)'s new guidelines recommend use of population-based trimester-specific reference range (RR) for thyrotropin (TSH) in pregnancy. The aim of this study was to determine first trimester TSH RR for a population of pregnant women in Rio de Janeiro State.

SUBJECTS AND METHODS

Two hundred and seventy pregnant women without thyroid illness, defined by National Academy of Clinical Biochemistry, and normal iodine status were included in this sectional study. This reference group (RG) had normal median urinary iodine concentration (UIC = 219 μg/L) and negative anti-thyroperoxidase antibodies (TPOAb). Twin pregnancy, trophoblastic disease and use of drugs or supplements that influence thyroid function were excluded. In a second step, we defined a more selective reference group (SRG, n = 170) by excluding patients with thyroiditis pattern on thyroid ultrasound and positive anti-thyroglobulin antibodies. This group also had normal median UIC. At a final step, a more selective reference group (MSRG, n = 130) was defined by excluding any pregnant women with UIC < 150 μg/L.

RESULTS

In the RG, median, 2.5th and 97.5th percentiles of TSH were 1.3, 0.1, and 4.4 mIU/L, respectively. The mean age was 270 ± 5.0 and the mean body mass index was 25.6 ± 5.2 kg/m2. In the SRG and MSRG, 2.5th and 975th percentiles were 0.06 and 4.0 (SRG) and 0.1 and 3.6 mIU/L (MSRG), respectively.

CONCLUSIONS

In the population studied,TSH upper limit in the first trimester of pregnancy was above 2.5 mIU/L. The value of 3.6 mIU/L, found when iodine deficiency and thyroiditis (defined by antibodies and ultrasound characteristics) were excluded, matches recent ATA guidelines.

Changes in biochemical tests in pregnancy and their clinical significance

Interpretation of laboratory investigations relies on reference intervals. Physiological changes in pregnancy may result in significant changes in normal values for many biochemical assays, and as such results may be misinterpreted as abnormal or mask a pathological state. The aims of this review are as follows: 1. To review the major physiological changes in biochemical tests in normal pregnancy. 2. To outline where these physiological changes are important in interpreting laboratory investigations in pregnancy. 3. To document the most common causes of abnormalities in biochemical tests in pregnancy, as well as important pregnancy-specific causes.

Iron Deficiency May Predict Greater Risk for Hypothyroxinemia: A Retrospective Cohort Study of Pregnant Women in China

BACKGROUND

Pregnant women are highly vulnerable to iron deficiency (ID) due to the increased iron needs during pregnancy. ID decreases circulating thyroid hormone concentrations likely through impairment of iron-dependent thyroid peroxidase. The present study aimed to explore the association between ID and hypothyroxinemia in a retrospective cohort of pregnant women in China.

METHODS

To investigate the relationship between ID and hypothyroxinemia, 723 pregnant women were retrospectively analyzed, including 675 and 309 women in the second and third trimesters, respectively. Trimester-specific hypothyroxinemia was defined as free thyroxine (fT4) levels below the 2.5th percentile of the reference range with normal serum thyrotropin (TSH) or TSH higher than the 97.5th percentile of the reference range in each trimester of pregnancy. Serum TSH, fT4, thyroid peroxidase antibodies, thyroglobulin antibodies, serum ferritin, soluble transferrin receptor, and urinary iodine concentrations were measured. Serum ferritin, soluble transferrin receptor, and total body iron were used to indicate the nutritional iron status.

RESULTS

Cross-sectional multiple linear regression analysis showed that iron status was positively associated with serum fT4 levels in the first and second trimesters of pregnancy, but not in the third trimester. Logistic regression analysis showed that ID was an independent risk factor for hypothyroxinemia (odds ratio = 14.86 [confidence interval 2.31-95.81], p = 0.005 in the first trimester and odds ratio = 3.36 [confidence interval 1.01-11.21], p = 0.048 in the second trimester). The prospective analysis showed that pregnant women with ID during the first trimester of pregnancy had lower serum fT4 levels and a higher rate of hypothyroxinemia in the second or third trimester than those without ID.

CONCLUSIONS

ID appears to be a risk factor to predict hypothyroxinemia in the first and second trimesters of pregnancy, but not in the third trimester. Pregnant women with ID in the first and second trimesters should be regarded as a high-risk group for maternal hypothyroxinemia.

The upper limit for TSH during pregnancy: why we should stop using fixed limits of 2.5 or 3.0 mU/l

Physiological changes necessitate the use of pregnancy-specific reference ranges for TSH and FT4 to diagnose thyroid dysfunction during pregnancy. Although many centers use fixed upper limits for TSH of 2.5 or 3.0 mU/L, this comment describeds new data which indicate that such cut-offs are too low and may lead to overdiagnosis or even overtreatment. The new guidelines of the American Thyroid Association have considerably changed recommendations regarding thyroid function reference ranges in pregnancy accordingly. Also a stepwise approach to interpreting these guidelines is discussed as well as the relevant role of FT4 in diagnosis.

Maternal thyroid hormone insufficiency during pregnancy and risk of neurodevelopmental disorders in offspring: A systematic review and meta-analysis

BACKGROUND

In the last 2 decades, several studies have examined the association between maternal thyroid hormone insufficiency during pregnancy and neurodevelopmental disorders in children and shown conflicting results.

AIM

This systematic review aimed to assess the evidence for an association between maternal thyroid hormone insufficiency during pregnancy and neurodevelopmental disorders in children. We also sought to assess whether levothyroxine treatment for maternal thyroid hormone insufficiency improves child neurodevelopment outcomes.

METHODS

We performed systematic literature searches in MEDLINE, EMBASE, PSYCinfo, CINAHL, AMED, BNI, Cochrane, Scopus, Web of Science, GreyLit, Grey Source and Open Grey (latest search: March 2017). We also conducted targeted web searching and performed forwards and backwards citation chasing. Meta-analyses of eligible studies were carried out using the random-effects model.

RESULTS

We identified 39 eligible articles (37 observational studies and 2 randomized controlled trials [RCT]). Meta-analysis showed that maternal subclinical hypothyroidism and hypothyroxinaemia are associated with indicators of intellectual disability in offspring (odds ratio [OR] 2.14, 95% confidence interval [CI] 1.20 to 3.83, P = .01, and OR 1.63, 95% CI 1.03 to 2.56, P = .04, respectively). Maternal subclinical hypothyroidism and hypothyroxinaemia were not associated with attention deficit hyperactivity disorder, and their effect on the risk of autism in offspring was unclear. Meta-analysis of RCTs showed no evidence that levothyroxine treatment for maternal hypothyroxinaemia or subclinical hypothyroidism reduces the incidence of low intelligence quotient in offspring.

LIMITATIONS

Although studies were generally of good quality, there was evidence of heterogeneity between the included observational studies (I² 72%-79%).

CONCLUSION

Maternal hypothyroxinaemia and subclinical hypothyroidism may be associated with intellectual disability in offspring. Currently, there is no evidence that levothyroxine treatment, when initiated 8- to 20-week gestation (mostly between 12 and 17 weeks), for mild maternal thyroid hormone insufficiency during pregnancy reduces intellectual disability in offspring.

Pregnancy outcomes are not altered by variation in thyroid function within the normal range in women free of thyroid disease

OBJECTIVE

In the recently revised guidelines on the management of thyroid dysfunction during pregnancy, treatment with thyroid hormone (LT4) is not recommended in women without thyroid autoimmunity (TAI) and TSH levels in the range 2.5-4.0 mIU/L, and in a recent study in that particular group of pregnant women, more complications were observed when a treatment with LT4 was given. The objective of the study was therefore to investigate whether variation in thyroid function within the normal (non-pregnant) range in women free of thyroid disease was associated with altered pregnancy outcomes?

DESIGN

Cross-sectional data analysis of 1321 pregnant women nested within an ongoing prospective collection of pregnant women's data in a single centre in Brussels, Belgium.

METHODS

Thyroid peroxidase antibodies (TPO-abs), thyroid-stimulating hormone (TSH), free T4 (FT4) and ferritin levels were measured and baseline characteristics were recorded. Women taking LT4, with TAI and thyroid function outside the normal non-pregnant range were excluded. Pregnancy outcomes and baseline characteristics were correlated with all TSH and FT4 levels within the normal range and compared between two groups (TSH cut-off < and ≥2.5 mIU/L).

RESULTS

Tobacco use was associated with higher serum TSH levels (OR: 1.38; CI 95%: 1.08-1.74); P = 0.009. FT4 levels were inversely correlated with age and BMI (rho = -0.096 and -0.089; P < 0.001 and 0.001 respectively) and positively correlated with ferritin levels (rho = 0.097; P < 0.001). Postpartum haemorrhage (>500 mL) was inversely associated with serum FT4 levels (OR: 0.35; CI 95%: 0.13-0.96); P = 0.040. Also 10% of women free of thyroid disease had serum TSH levels ≥2.5 mIU/L.

CONCLUSIONS

Variation in thyroid function during the first trimester within the normal (non-pregnant) range in women free of thyroid disease was not associated with altered pregnancy outcomes. These results add evidence to the recommendation against LT4 treatment in pregnant women with high normal TSH levels and without TPO antibodies.

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.

Thyroid Allostasis-Adaptive Responses of Thyrotropic Feedback Control to Conditions of Strain, Stress, and Developmental Programming

The hypothalamus-pituitary-thyroid feedback control is a dynamic, adaptive system. In situations of illness and deprivation of energy representing type 1 allostasis, the stress response operates to alter both its set point and peripheral transfer parameters. In contrast, type 2 allostatic load, typically effective in psychosocial stress, pregnancy, metabolic syndrome, and adaptation to cold, produces a nearly opposite phenotype of predictive plasticity. The non-thyroidal illness syndrome (NTIS) or thyroid allostasis in critical illness, tumors, uremia, and starvation (TACITUS), commonly observed in hospitalized patients, displays a historically well-studied pattern of allostatic thyroid response. This is characterized by decreased total and free thyroid hormone concentrations and varying levels of thyroid-stimulating hormone (TSH) ranging from decreased (in severe cases) to normal or even elevated (mainly in the recovery phase) TSH concentrations. An acute versus chronic stage (wasting syndrome) of TACITUS can be discerned. The two types differ in molecular mechanisms and prognosis. The acute adaptation of thyroid hormone metabolism to critical illness may prove beneficial to the organism, whereas the far more complex molecular alterations associated with chronic illness frequently lead to allostatic overload. The latter is associated with poor outcome, independently of the underlying disease. Adaptive responses of thyroid homeostasis extend to alterations in thyroid hormone concentrations during fetal life, periods of weight gain or loss, thermoregulation, physical exercise, and psychiatric diseases. The various forms of thyroid allostasis pose serious problems in differential diagnosis of thyroid disease. This review article provides an overview of physiological mechanisms as well as major diagnostic and therapeutic implications of thyroid allostasis under a variety of developmental and straining conditions.

Risk factors and a clinical prediction model for low maternal thyroid function during early pregnancy: two population-based prospective cohort studies

BACKGROUND

Low maternal thyroid function during early pregnancy is associated with various adverse outcomes including impaired neurocognitive development of the offspring, premature delivery and abnormal birthweight.

AIM

To aid doctors in the risk assessment of thyroid dysfunction during pregnancy, we set out to investigate clinical risk factors and derive a prediction model based on easily obtainable clinical variables.

METHODS

In total, 9767 women during early pregnancy (≤18 week) were selected from two population-based prospective cohorts: the Generation R Study (N = 5985) and the ABCD study (N = 3782). We aimed to investigate the association of easily obtainable clinical subject characteristics such as maternal age, BMI, smoking status, ethnicity, parity and gestational age at blood sampling with the risk of low free thyroxine (FT4) and elevated thyroid stimulating hormone (TSH), determined according to the 2·5th-97·5th reference range in TPOAb negative women.

RESULTS

BMI, nonsmoking and ethnicity were risk factors for elevated TSH levels; however, the discriminative ability was poor (range c-statistic of 0·57-0·60). Sensitivity analysis showed that addition of TPOAbs to the model yielded a c-statistic of 0·73-0·75. Maternal age, BMI, smoking, parity and gestational age at blood sampling were risk factors for low FT4, which taken together provided adequate discrimination (range c-statistic of 0·72-0·76).

CONCLUSIONS

Elevated TSH levels depend predominantly on TPOAb levels, and prediction of elevated TSH levels is not possible with clinical characteristics only. In contrast, the validated clinical prediction model for FT4 had high discriminative value to assess the likelihood of low FT4 levels.