Identifying and treating subclinical thyroid dysfunction in pregnancy: emerging controversies

Description of thyroid disorders the year before conception: a population-based study

Objective

This study aimed to monitoring the prevalence of previously identified thyroid disorders and hypothyroidism monitoring before pregnancy.

Material and methods

A retrospective cross-sectional study of women whose pregnancies occurred between 2014 and 2016 was conducted, including 120,763 pregnancies in Catalonia (Spain). The presence of thyroid disorders in women was based on disease diagnostic codes and/or prescription of levothyroxine or antithyroid drugs. To evaluate the thyroid disorder diagnosis and monitoring, thyrotropin (TSH), free T4 (FT4), antiperoxidase antibody (TPOAb), and anti-TSH receptor antibody (TRAb) records were gathered and categorised according to the reference values of each laboratory.

Results

The prevalence of recorded thyroid disorders before the last menstrual period was 5.09% for hypothyroidism and 0.64% for hyperthyroidism,showing a significant increase with age. A thyroid monitoring test was not performed in the year before the last menstrual period in approximately 40% of women with a known thyroid disorder. Amongst the women with hypothyroidism who underwent a TSH test, 31.75% showed an above-normal result. Amongst women previously unknown to have thyroid disorders, 3.12% had elevated TSH levels and 0.73% had low TSH levels.

Conclusion

A high percentage of Catalan women with a known thyroid disorder were not properly monitored during the year before pregnancy. Amongst those monitored, more than one-third had TSH values outside the reference range. Therefore, it is important to evaluate women with thyroid disorders during pre-pregnancy visits.

Effect of levothyroxine treatment on fetal growth among women with mild subclinical hypothyroidism and thyroid peroxidase antibody negative: a cohort study

BACKGROUND

Some clinicians used levothyroxine (LT4) treatment for mild subclinical hypothyroidism (SCH) pregnant women (2.5 < thyroid-stimulating hormone (TSH) ≤ the pregnancy-specific reference range with normal free thyroxine (FT4) level) with thyroid peroxidase antibody negative (TPOAb^-), although the recent clinical guideline did not recommend it. It is unknown whether LT4 treatment for pregnant women with mild SCH and TPOAb^- have impact on fetal growth. Therefore, the aim of the study was to investigate the effect of LT4 treatment on fetal growth and birth weight among mild SCH pregnant women with TPOAb^-.

METHODS

This was a birth cohort study including 14,609 pregnant women between 2016 and 2019 in Tongzhou Maternal and Child Health Hospital of Beijing, China. Pregnant women were divided into 3 groups as follows: Euthyroid (n = 14,285, 0.03 ≤ TSH ≤ 2.5mIU/L, normal FT4), TPOAb^-; Untreated mild SCH with TPOAb^- (n = 248, 2.5 < TSH ≤ 2.9mIU/L, normal FT4, without LT4 treatment); Treated mild SCH with TPOAb^- (n = 76, 2.5 < TSH ≤ 2.9mIU/L, normal FT4, with LT4 treatment). The main outcome measures were Z-scores of fetal growth indicators (abdominal circumference (AC), biparietal diameter (BPD), femur length (FL), head circumference (HC), estimated fetal weight (EFW)), fetal growth restriction (FGR) and birth weight.

RESULTS

There was no difference in fetal growth indicators and birth weight between the untreated mild SCH women with TPOAb^- and the euthyroid pregnant women. But the HC Z-score was lower in the LT4 treated mild SCH women with TPOAb^-, compared with the euthyroid pregnant women (β = -0.223, 95%CI: -0.422, -0.023). The LT4 treated mild SCH women with TPOAb^- had lower fetal HC Z-score (β = -0.236, 95%CI: -0.457, -0.015), compared with the untreated mild SCH women with TPOAb^-.

CONCLUSIONS

We observed that LT4 treatment for mild SCH with TPOAb^- was associated with decreased fetal HC, which was not observed for untreated mild SCH women with TPOAb^-. The adverse effect of LT4 treatment for mild SCH with TPOAb^- provided new evidence for the recent clinical guideline.

Executive summary of the SEEN (Sociedad Española de Endocrinología y Nutrición[Spanish Society of Endocrinology and Nutrition])-SEGO (Sociedad Española deGinecología y Obstetricia [Spanish Society of Gynaecology and Obstetrics]) consensusdocument on the management of thyroid dysfunction during pregnancy

During pregnancy, thyroid function disorders are associated with multiple complications, both maternal and foetal. In recent years, numerous Clinical Practice Guidelines have been developed to facilitate the identification and correct management of thyroid disease in pregnant women. However, this proliferation of guidelines has led to confusion by proposing different cut-off points for reference values and different recommendations for similar situations. For this reason, the Sociedad Española de Endocrinología y Nutrición and the Sociedad Española de Ginecología y Obstetricia have prepared this Consensus Document, with the aim of creating a framework for joint action to unify criteria for the diagnosis and treatment of thyroid dysfunction in these patients. The document is structured to answer the most frequently asked questions in clinical practice, grouped into five sections: 1/Reference values for thyroid function tests and screening during pregnancy 2/Iodine nutrition 3/Hypothyroidism and pregnancy 4/Hyperthyroidism and pregnancy 5/ Thyroid autoimmunity.

Thyroid autoimmunity and pregnancy in euthyroid women

Women with thyroid autoimmunity (TAI), predominately characterized by increased levels of thyroid peroxidase antibody (TPOAb), are at risk for developing pregnancy related complications. In this review, we discuss the importance of TAI during natal and perinatal stages. Before pregnancy, TAI is associated with higher mean serum TSH levels and certain causes of subfertility. During pregnancy, TAI increases the risk of an insufficient response of the thyroid to an increasing strain induced by pregnancy, and consequently (subclinical) hypothyroidism might develop. Euthyroid women with TAI have a higher rate of maternal and foetal complications, but it seems that causality cannot be pinned down to thyroid dysfunction alone. Almost half of the women known with TAI prior to pregnancy will also develop post-partum thyroiditis (PPT). However, any relation between PPT and post-partum depression remains uncertain. More research is required to explain possible associations between TAI and pregnancy morbidities, and studies should focus on a better understanding of TAI as such. Given the many unanswered questions, at present, it is not recommended to screen all (potentially) pregnant women for the presence of TAI.

[Thyroid disease during pregnancy]

Thyroid disease is the second most endocrinopathy during pregnancy 1. Thyroid dysfunction affects 2-3 % of pregnant women 2. Early diagnosis and initiation of therapy are important due to the potential complications in both mother and fetus. This article provides an overview of current recommendations regarding thyroid diagnostics and constellations during pregnancy that require therapy.

Association of Differential Metabolites With Small Intestinal Microflora and Maternal Outcomes in Subclinical Hypothyroidism During Pregnancy

Objective

To investigate the association of differential metabolites with small intestinal microflora and maternal outcomes in subclinical hypothyroidism (SCH) during pregnancy.

Methods

The plasma of pregnant women in the SCH group and control group was analyzed by liquid chromatography-mass spectrometry (LC-MS), obtaining differential metabolites. Then, methane and hydrogen breath tests were performed in both groups, and basic clinical data and maternal outcome information were collected. Finally, differential metabolites were analyzed for small intestinal bacterial overgrowth (SIBO) and pregnancy outcomes using Spearman correlation analysis.

Results

(1) Multivariate statistics: There were 564 different metabolites in positive ion mode and 226 different metabolites in negative ion mode. (2) The positive rate of the methane hydrogen breath test in the SCH group was higher than that in the control group (p<0.05). (3) KEGG pathway analysis revealed that differential metabolites were mainly involved in bile secretion, cholesterol metabolism, and other pathways. (4) Serum cholesterol (TC) and triglyceride (TG) levels and hypertensive disorder complicating pregnancy (HDCP) were higher in the SCH group (p<0.05), and newborn birth weight (BW) was lower than that in the control group (p<0.05). (5) SIBO was negatively correlated with glycocholic acid and BW, and positively correlated with TC. Glycocholic acid was negatively correlated with TG but positively correlated with BW. TG was positively correlated with HDCP.

Conclusion

Differential metabolites in the SCH group during pregnancy were disordered with small intestinal bacteria, which may affect pregnancy outcomes, and bile acids and cholesterol may be potential biomarkers for studying their mechanism of action.

Use of levothyroxine among pregnant women with subclinical hypothyroidism in the United Kingdom: A population-based assessment

Our study aimed to describe levothyroxine prescription patterns and trends over time among pregnant women with subclinical hypothyroidism (SCH) in the United Kingdom.

We used data from the Clinical Practice Research Datalink linked to its Pregnancy Register and the Hospital Episode Statistics database from 1998 to 2017. The study population included women with a diagnosis of SCH or an abnormal thyroid‐simulated hormone (TSH) level one year prior to or during pregnancy. We compared characteristics between women who received a prescription for levothyroxine during pregnancy and those who did not. We further described the timing, dose, duration, and temporal trends of levothyroxine prescriptions.

Our cohort included 6,757 pregnancies from 6,287 women with SCH, of whom 10% received levothyroxine during pregnancy. Among women who received levothyroxine, most received their first prescription during the first trimester (median gestational age: 7 weeks; interquartile range [IQR]: 0, 16) with a median daily dosage of 50 mcg (IQR: 50, 73). Levothyroxine prescription varied over time, decreasing from 23% of pregnant women in 1998 to 7.5% in 2003, remaining stable until 2014, and increasing to 12.5% in 2016. Smoking, diabetes, polycystic ovary syndrome, infertility, timing of SCH diagnosis, age, TSH level at diagnosis, and general practice regions were associated with prescription.

Few women with SCH received levothyroxine during pregnancy, and treatment varied by patient characteristics and geographical regions. These results highlight the need to increase awareness among healthcare providers and will guide future studies that explore barriers to initiating levothyroxine treatment for women with SCH during pregnancy.

A Clinical Debate: Subclinical Hypothyroidism

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Perinatal Outcomes and Risk Factors for Preterm Birth in Twin Pregnancies in a Chinese Population: A Multi-center Retrospective Study

Background: Twin pregnancies are associated with an increased risk of adverse maternal and neonatal outcomes, mainly owing to prematurity. Few studies have evaluated the risk factors for preterm birth (PTB) in Chinese population. The objective of this study is to present the short-term maternal-neonatal outcomes, investigating the potential risk factors associated with preterm birth in Chinese twin pregnancies.

Methods: A multi-center retrospective study of women pregnant with twins ≥28 weeks of gestation was conducted. Maternal and neonatal outcomes were analyzed. Logistic regression was used to identify potential risk factors for PTB before 37, 34, and 32 weeks, respectively.

Results: A total of 3,288 twin pregnancies and 6,576 neonates were included in 99,585 pregnancies. The rate of twin pregnancy was 3.3%, while the PTB rate before 37, 34, and 32 weeks among this population were 62.1, 18.8, and 10.4%, respectively. Logistic regression revealed that monochorionicity [Odds ratio (OR) 3.028, 95% confident interval (CI) 2.489–3.683, P < 0.001], gestational weight gain (GWG) <10 kg (OR 2.285, 95% CI 1.563–3.339, P < 0.001) and GWG between 10 and 15 kg (OR 1.478, 95% CI 1.188–1.839, P < 0.001), preeclampsia (PE) (OR 3.067, 95% CI 2.142–4.390, P < 0.001), and intrahepatic cholestasis of pregnancy (ICP) (OR 3.122, 95% CI 2.121–4.596, P < 0.001) were the risk factors for PTB before 37 weeks. Monochorionicity (OR 2.865, 95% CI 2.344–3.501, P < 0.001), age < 25 years (OR 1.888, 95% CI 1.307–2.728, P = 0.001), and GWG <10 kg (OR 3.100, 95% CI 2.198–4.372, P < 0.001) were risk factors for PTB before 34 weeks. Monochorionicity (OR 2.566, 95% CI 1.991–3.307, P < 0.001), age younger than 25 years (OR 1.964, 95% CI 1.265–3.048, P = 0.003), and GWG <10 kg (OR 4.319, 95% CI 2.931–6.364, P < 0.001) were the risk factors for PTB before 32 weeks.

Conclusions: Monochorionicity and GWG <10 kg were two major risk factors for PTB before 32, 34, and 37 weeks, whereas maternal age, PE, and ICP were also risk factors for PTB in specific gestational age.

Controversial Screening for Thyroid Dysfunction in Preconception and Pregnancy: An Evidence-Based Review

Objective: To evaluate the recommendations on the most adequate screening method (universal or selective) for thyroid dysfunction. Although thyroid dysfunction is a common disorder in fertile women and untreated cases may have negative maternal, fetal and neonatal outcomes, its screening in preconception and early pregnancy is controversial.

Materials and methods: An evidence-based review was conducted to identify publications since 2017 of American Thyroid Association (ATA) guidelines, according to the following Population, Intervention, Comparison, Outcomes and Study (PICOS): women in preconception or pregnancy without thyroid disease who underwent universal or selective screening for thyroid dysfunction. Study selection obeyed the PRISMA criteria.

Results: We included 15 of 325 publications. The 2017 ATA guidelines recommend selective screening in both preconception and pregnancy. The only two reviews on preconception recommended universal screening. For pregnancy, nine articles suggested universal screening, while a prospective study advocated selective screening. The main benefits advocated for universal screening were easy and low-cost tests; absence of missed diagnosis; safe and inexpensive treatment and its potential in preventing negative outcomes. Iodine deficiency is a decisive indication, but it was not evaluated in all clinical studies. Screening harms and knowledge gaps were the main arguments against universal screening. There are very few cost-effectiveness studies.

Conclusion: We recommend universal screening for thyroid dysfunction in early pregnancy, which is a distinct point of view from 2017 ATA guidelines (weak recommendation, low-quality evidence). It is not possible to make a formal recommendation for preconception (insufficient evidence). We strongly suggest an individualized analysis by each country.

Reference values and the effect of clinical parameters on thyroid hormone levels during early pregnancy

OBJECTIVE

Thyroid dysfunction is a common endocrine problem during pregnancy; correct diagnosis and appropriate treatments are essential to avoid adverse pregnancy outcomes. Besides, it is vital to identify and quantify the major risk factors for gestational thyroid dysfunction, including thyroid autoimmunity, human chorionic gonadotropin (HCG) concentration, body mass index (BMI) and parity. The study objective was to establish reference ranges during early pregnancy and to explore the relationship between risk factors and thyroid stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyroxine (FT3).

DESIGN, PATIENTS AND MEASUREMENTS

To establish the reference ranges of thyroid hormone during early pregnancy in China and to identify the risk factors for thyroid dysfunction, woman in the first trimester of pregnancy (4-12 weeks gestation) were recruited. After excluding thyroid peroxidase antibody (TPO-Ab) positive and/or thyroglobulin antibody (TG-Ab) positive women, previous thyroid disease, a lack of iodine intake, reference values were calculated by 2.5th to 97.5th percentiles.

RESULTS

After exclusion of TPO-Ab and/or TG-Ab positive women, reference values were as follows: TSH, 0.11-3.67 mIU/l; FT3, 3.19-5.91 pmol/l; FT4 10.95-16.79 pmol/l. Higher BMI was associated with lower FT4 concentrations (P=0.005). In multiple regression analysis, TSH was significantly and positively associated with TG (P=0.03). Maternal parity and maternal age may be risk factors for the abnormal thyroidal response to hCG concentrations.

CONCLUSIONS

Our study defined first trimester-specific reference ranges for serum TSH, FT4, FT3 in a Chinese population, and demonstrated that BMI ≥23kg/m2, maternal parity ≥3 and maternal age ≥30 years may increase the risk of thyroid dysfunction.

Thyroid hormones in ovarian follicular fluid: Association with oocyte retrieval in women undergoing assisted fertilization procedures

Objective:

Our aim was to analyze the role of thyroid hormones in follicular fluid (FF) in relation to the number of oocytes retrieved in women recruited for an assisted fertilization procedure.

Methods:

Retrospective cohort study of 51 women 37.5±3.3 years, range 29-42, evaluated after a controlled ovarian stimulation protocol in a University Hospital. FF was sampled by transvaginal ultrasound-guided aspiration after ovarian hyperstimulation and we measured T3 (T3f), T4 (T4f), TSH (TSHf) and free T4 (T4ff). The oocyte maturation rate was calculated as: Number of metaphase II oocytes/Number of oocytes retrieved x 100. Statistical analysis was performed using the SPSS-19 software.

Results:

Hormone levels in FF were: TSHf 1.3µIU/ml (0.4 - 2.7), T3f: 1.52±0.46 nmol/L, T4f 88.8±30.9nmol/L and T4ff: 15.44±2.57pmol/L. The number of oocytes recovered was dependent onT4f following the equation: Log (oocyte) = 0.379+0.042*T4f (r:0.352, p=0.012). After a logistic regression model analysis, T3f showed a tendency to be associated with the OMR: OR (95 % CI)= 0.977 (0.954 to 1.001), p=0.057.

Conclusions:

The correlation found between thyroid hormones and the number of oocytes retrieved suggests an interaction between thyroid and gonadal axes in relation to follicular development.

Effect of levothyroxine supplementation on pregnancy loss and preterm birth in women with subclinical hypothyroidism and thyroid autoimmunity: a systematic review and meta-analysis

BACKGROUND

Subclinical hypothyroidism (SCH) and thyroid autoimmunity (TAI) are associated with adverse pregnancy outcomes such as pregnancy loss and preterm birth. However, the ability of levothyroxine (LT4) supplementation to attenuate the risks of these outcomes remains controversial.

OBJECTIVE AND RATIONALE

This systematic review and meta-analysis was conducted to determine the effect of LT4 supplementation on pregnancy loss rate (PLR) and preterm birth rate (PBR) among pregnant women with SCH and TAI.

SEARCH METHODS

A systematic literature search of the PubMed, EMBASE, Web of Science and Cochrane Controlled Trials Register databases and Clinicaltrials.gov was performed to identify all relevant English studies published up to April 2018. The following terms were used for the search: [subclinical hypothyroidism OR thyroid autoimmunity OR thyroperoxidase antibody (TPO-Ab) OR thyroglobulin antibodies (Tg-Ab)] AND (levothyroxine OR euthyrox) AND [pregnancy outcome OR miscarriage OR abortion OR pregnancy loss OR preterm birth OR premature delivery OR early labo(u)r]. The reference lists of the relevant publications were also manually searched for related studies. Published manuscripts were included if they reported data on pregnancy loss, preterm birth or both. We separately analysed the pooled effects of LT4 supplementation on PLR and PBR in women with SCH and TAI.

OUTCOMES

Overall, 13 eligible studies including 7970 women were included in the meta-analysis. Eight and five of these studies were randomized controlled trials (RCTs) and retrospective studies, respectively. The pooled results indicated that LT4 supplementation significantly decreased the PLR [relative risk (RR) = 0.56, 95% confidence interval (CI): 0.42-0.75, I2 = 1%, 12 studies] and PBR (RR = 0.68, 95% CI: 0.51-0.91, I2 = 21%, eight studies) in women with SCH and/or TAI. We further found that LT4 supplementation significantly decreased the risk of pregnancy loss (RR = 0.43, 95% CI: 0.26-0.72, P = 0.001, I2 = 0%) but not of preterm birth (RR = 0.67, 95% CI: 0.41-1.12, P = 0.13, I2 = 0%) in women with SCH. Furthermore, LT4 supplementation significantly decreased the risks of both pregnancy loss (RR = 0.63, 95% CI: 0.45-0.89, P = 0.009, I2 = 0%) and preterm birth (RR = 0.68 95% CI: 0.48-0.98, P = 0.04, I2 = 46%) in women with TAI. These results were consistent when only RCTs were included in the analysis. Further, in women with SCH, LT4 supplementation reduced the risk of pregnancy loss in pregnancies achieved by assisted reproduction (RR = 0.27, 95% CI: 0.14-0.52, P < 0.001, I2 = 14%) but not in naturally conceived pregnancies (RR = 0.60, 95% CI: 0.28-1.30, P = 0.13, I2 = 0%). By contrast, in women with TAI, LT4 supplementation reduced the risks of both pregnancy loss (RR = 0.61, 95% CI: 0.39-0.96, P = 0.03, I2 = 0%) and preterm birth (RR = 0.49, 95% CI: 0.30-0.79, P = 0.003, I2 = 0%) in naturally conceived pregnancies but not in pregnancies achieved by assisted reproduction (RR = 0.68, 95% CI: 0.40-1.15, P = 0.15, I2 = 0% for pregnancy loss and RR = 1.20, 95% CI: 0.68-2.13, P = 0.53, I2 not applicable for preterm birth).

WIDER IMPLICATIONS

This meta-analysis confirmed the beneficial effects of LT4 supplementation, namely the reduced risks of pregnancy loss and preterm birth, among pregnant women with SCH and/or TAI. The different effects of LT4 supplementation on naturally conceived pregnancies and pregnancies achieved by assisted reproduction in women with SCH and/or TAI suggest that these women should be managed separately. Due to the limited number of studies included in this meta-analysis, especially in the subgroup analysis, further large RCTs and fundamental studies are warranted to confirm the conclusions and better clarify the molecular mechanism underlying these associations.

Slightly elevated thyrotropin levels in pregnancy in our clinical practice

OBJECTIVE

The aim of this study was to assess the incidence of obstetric and neonatal complications in pregnant women with "normal" thyroid-stimulating hormone (TSH) levels in the first trimester (group A) and to compare them with those with "slightly elevated" TSH (SET) levels treated with levothyroxine (group B2) or not treated (group B1).

METHODS

A total of 2375 women who had been performed laboratory tests in their first trimester of pregnancy were detected at our hospital between April 2015 and August 2017. Of these, 469 patients with SET were prospectively detected and randomized to groups B1 (227) and B2 (242). They were monitored prospectively until 6 months after delivery. Data of the control group (n=1906, group A) were retrospectively reviewed. A total of 1745 women were analyzed. Variables assessed included demographic and clinical characteristics and complications of pregnancy and delivery.

RESULTS

A, B1, and B2 had similar clinical characteristics. There were no statistically significant differences in complications between the three groups during pregnancy, except in that natural deliveries were more common in group A as compared to group B1 (76.8% vs. 68.7%, p 0.017) and group B2 (66.3%), p<0.002). There were more induced deliveries in groups B1 (35.8%), and B2 (36.2%) than in group A (18.4%), p<0.01. Although the recommended TSH level was achieved in the second and third trimesters, no benefit could be found of treatment of SET.

CONCLUSION

Although there were less natural deliveries and more induced deliveries in patients with SET, treatment with levothyroxine could not reverse this situation, despite achievement of levels considered appropriate in the second and third trimester.

Practice Variation in the Care of Subclinical Hypothyroidism During Pregnancy: A National Survey of Physicians in the United States

Evidence regarding the effects of subclinical hypothyroidism (SCH) on adverse pregnancy outcomes and the ability of levothyroxine (LT4) treatment to prevent them is unclear. Available recommendations for the management of SCH during pregnancy are inconsistent. We conducted a nationwide survey among physicians assessing their knowledge of and current practices in the care of SCH in pregnancy and compared these with the most recent American Thyroid Association (ATA) recommendations. In this cross-sectional study, an online survey was sent to active US members of the Endocrine Society. This survey included questions about current practices and clinical scenarios aimed at assessing diagnostic evaluation, initiation of therapy, and follow-up in pregnant women with SCH. In total, 162 physicians completed the survey. ATA guidelines were reviewed by 76%, of whom 53% indicated that these guidelines actually changed their practice. Universal screening was the preferred screening approach (54%), followed by targeted screening (30%). For SCH diagnosis, most respondents (52%) endorsed a TSH level >2.5 mIU/L as a cutoff, whereas 5% endorsed a population-based cutoff as recommended by the ATA. The decision to initiate treatment varied depending on the specific clinical scenario; however, when LT4 was initiated, respondents expected a small/very small reduction in maternofetal complications. In conclusion, despite recently updated guidelines, there is still wide variation in clinical practices regarding the care of women with SCH in pregnancy. Highly reliable randomized trials are required to evaluate the effectiveness of the most uncertain treatment practices on the care of pregnant women with SCH.

Subclinical hypothyroidism in pregnancy

PURPOSE OF REVIEW

Subclinical hypothyroidism (SCH) is a common diagnosis among women of reproductive age. The importance of sufficient maternal thyroid supply during pregnancy is well known. Nevertheless, the effects of SCH during pregnancy and the efficacy of its treatment on maternofetal outcomes are not well established. This review discusses the recent evidence on SCH in pregnancy and how this evidence is reflected in current clinical care.

RECENT FINDINGS

Recent observational studies have found a positive association between SCH during pregnancy and adverse maternal, neonatal and offspring outcomes, mainly in thyroid peroxidase autoantibody positive women. Although interventional studies have shown a benefit of levothyroxine (LT4) treatment on selected pregnancy outcomes, there was no effect on offspring neurodevelopment.

SUMMARY

Current evidence strengthens the association between SCH with both maternofetal and offspring adverse outcomes. An earlier and more individualized diagnostic assessment taking into consideration predictors of thyroid dysfunction and major risk factors for complications could result in better management of SCH during pregnancy. The effectiveness of LT4 on improving maternofetal and long-term offspring outcomes is still not fully elucidated.

Hypothyroidism in Pregnancy

Thyroid hormone is essential for pregnancy and ensuring fetal development. Pregnancy also places substantial demands on the thyroid axis. Overt hypothyroidism is associated with substantial adverse obstetric and offspring outcomes and requires treatment. Borderline thyroid dysfunction is common in women and associated with adverse obstetric and offspring outcomes, although benefits of screening for and treating borderline thyroid function are unclear. Many women are established on thyroid hormone replacement before pregnancy and doses need increasing during pregnancy. Care is taken to prevent overreplacement. Universal thyroid screening in pregnancy is being undertaken in several countries, although it remains a matter of debate.

Individualised requirements for optimum treatment of hypothyroidism: complex needs, limited options

Levothyroxine (LT4) therapy has a long history, a well-defined pharmacological profile and a favourable safety record in the alleviation of hypothyroidism. However, questions remain in defining the threshold for the requirement of treatment in patients with subclinical hypothyroidism, assessing the dose adequacy of the drug, and selecting the best treatment mode (LT4 monotherapy versus liothyronine [LT3]/LT4 combinations) for subpopulations with persisting complaints. Supplied as a prodrug, LT4 is enzymatically converted into the biologically more active thyroid hormone, triiodothyronine (T3). Importantly, tetraiodothyronine (T4) to T3 conversion efficiency may be impaired in patients receiving LT4, resulting in a loss of thyroid-stimulating hormone (TSH)-mediated feed-forward control of T3, alteration of the interlocking equilibria between serum concentrations of TSH, free thyroxine (FT4), and free triiodothyonine (FT3), and a decrease in FT3 to FT4 ratios. This downgrades the value of the TSH reference system derived in thyroid health for guiding the replacement dose in the treatment situation. Individualised conditionally defined setpoints may therefore provide appropriate biochemical targets to be clinically tested, together with a stronger focus on clinical presentation and future endpoint markers of tissue thyroid state. This cautionary note encompasses the use of aggregated statistical data from clinical trials which are not safely applicable to the individual level of patient care under these circumstances.

Screening for Thyroid Dysfunction in Pregnancy With Targeted High-Risk Case Finding: Can It Be Improved?

CONTEXT AND OBJECTIVE

Targeted screening is proposed for the detection of thyroid dysfunction in pregnant women rather than universal screening (US). We aimed to determine the detection rate of subclinical hypothyroidism (SCH) and overt hypothyroidism (OH) based on American Thyroid Association guidelines (ATA-GL) and whether it could be improved.

DESIGN, SETTING, AND PARTICIPANTS

Cross-sectional study of 1832 pregnant women in a single center. Thyroid function (TSH and free T4) and iron status were determined. The high-risk group (HRG) included women with one or more ATA-GL risk factors and the low-risk group (LRG) included women without. Participants with other risk factors [body mass index (BMI) 30 to 39.9 kg/m2, Caucasian background] were classified as HRG+ and those with iron deficiency as HRG++.

RESULTS

The HRG included 64% of women and the LRG included 36% (P < 0.001). Of all participants, 4.5% had SCH and 0.5% OH. The detection rate of SCH and OH was comparable between the LRG and HRG (46% vs 54% and 25% vs 75%; P = 0.560 and 0.157, respectively). In the HRG, the detection rate of SCH was lower than that of US (54% vs 100%; P < 0.001), but that of OH was comparable (75%; P = 0.596). The detection rate of SCH in the HRG+ and HRG++ was comparable to that in the US group (81% and 88% vs 100%; P = 0.220 and 0.439, respectively).

CONCLUSIONS

Targeted high-risk case finding screening was not effective for the detection of SCH but performed better for OH. When obesity in the range BMI 30 to 39.9 kg/m2 and a Caucasian background were included as risk factors, the detection rate of SCH became comparable with that of US.

Risk factors for gestational diabetes: An umbrella review of meta-analyses of observational studies

BACKGROUND/OBJECTIVE

Gestational diabetes mellitus (GDM) is a common pregnancy complication, with complex disease mechanisms, and several risk factors may contribute to its onset. We performed an umbrella review to summarize the evidence from meta-analyses of observational studies on risk factors associated with GDM, evaluate whether there are indications of biases in this literature and identify which of the previously reported associations are supported by convincing evidence.

METHODS

We searched PubMed and ISI Web of Science from inception to December 2018 to identify meta-analyses examining associations between putative risk factors for GDM. For each meta-analysis we estimated the summary effect size, the 95% confidence interval, the 95% prediction interval, the between-study heterogeneity, evidence of small-study effects, and evidence of excess-significance bias.

RESULTS

Thirty eligible meta-analyses were identified, providing data on 61 associations. Fifty (82%) associations had nominally statistically significant findings (P<0.05), while only 15 (25%) were significant at P<10-6 under the random-effects model. Only four risk factors presented convincing evidence:, low vs. normal BMI (cohort studies), BMI ~30-35 kg/m2 vs. normal BMI, BMI >35 kg/m2 vs. normal BMI, and hypothyroidism.

CONCLUSIONS

The compilation of results from synthesis of observational studies suggests that increased BMI and hypothyroidism show the strongest consistent evidence for an association with GDM. Diet and lifestyle modifications in pregnancy should be tested in large randomized trials. Our findings suggest that women with known thyroid disease may be offered screening for GDM earlier in pregnancy.

Zebrafish duox mutations provide a model for human congenital hypothyroidism

Thyroid dyshormonogenesis is a leading cause of congenital hypothyroidism, a highly prevalent but treatable condition. Thyroid hormone (TH) synthesis is dependent on the formation of reactive oxygen species (ROS). In humans, the primary sources for ROS production during thyroid hormone synthesis are the NADPH oxidases DUOX1 and DUOX2. Indeed, mutations in DUOX1 and DUOX2 have been linked with congenital hypothyroidism. Unlike humans, zebrafish has a single orthologue for DUOX1 and DUOX2. In this study, we investigated the phenotypes associated with two nonsense mutant alleles, sa9892 and sa13017, of the single duox gene in zebrafish. Both alleles gave rise to readily observable phenotypes reminiscent of congenital hypothyroidism, from the larval stages through to adulthood. By using various methods to examine external and internal phenotypes, we discovered a strong correlation between TH synthesis and duox function, beginning from an early larval stage, when T₄ levels are already noticeably absent in the mutants. Loss of T₄ production resulted in growth retardation, pigmentation defects, ragged fins, thyroid hyperplasia/external goiter and infertility. Remarkably, all of these defects associated with chronic congenital hypothyroidism could be rescued with T₄ treatment, even when initiated when the fish had already reached adulthood. Our work suggests that these zebrafish duox mutants may provide a powerful model to understand the aetiology of untreated and treated congenital hypothyroidism even in advanced stages of development.

This article has an associated First Person interview with the first author of the paper.

Summary: Zebrafish harbouring two loss-of-function alleles of the single duox gene exhibit various adult phenotypes reminiscent of human congenital hypothyroidism.

Effect of Thyroid Hormones on Neurons and Neurodevelopment

This review focuses on the current knowledge of the effects of thyroid hormones on central nervous system differentiation and development in animals and the human fetal brain. The outcomes of children with congenital hypothyroidism and of newborns with hypothyroid pregnant mothers are emphasized, focusing on how therapies could affect and especially improve the outcomes.

The Impact of Subclinical Hypothyroidism on Adverse Perinatal Outcomes and the Role of Thyroid Screening in Pregnancy

Subclinical hypothyroidism (SCH) is a mild form of hypothyroidism that is common among women of childbearing age. The impact of SCH on adverse perinatal outcomes is unclear and universal screening for thyroid function before or during pregnancy is also much debated. In the present retrospective cohort study on 7,587 women from Shanghai, we assessed whether SCH was associated with adverse perinatal outcomes. The relationship between the risks of adverse outcomes and the time of screening and LT4 treatment status for SCH were also evaluated. SCH was associated with hypertensive disorders of pregnancy (HDP) [odds ratio (OR): 4.04; 95% confidence interval (CI): 1.85-8.84; P = 0.000]. After classification into four different groups based on the time of screening for thyroid function, the increased likelihood of HDP persisted in those diagnosed with SCH in the first and second trimesters (OR: 9.69; 95% CI: 1.73-54.48; P = 0.01 and OR: 3.66; 95% CI: 1.07-12.57, P = 0.03, respectively). The diagnosis of SCH in the preconception period and the third trimester was not significantly associated with HDP and other adverse perinatal outcomes. Five out of 120 (5/120) treated women (4.17%) vs. 4/45 untreated women (8.89%) developed HDP, 4/5 were treated after conception. The results indicate that during pregnancy, SCH conferred an increased risk of HDP, particularly in women diagnosed with the disorder in the first and second trimesters.

A 2018 Italian and Romanian Survey on Subclinical Hypothyroidism in Pregnancy

OBJECTIVES

Pregnancy induces changes in thyroid function, and thyroid dysfunction during gestation is associated with adverse outcomes. We examined the management of subclinical hypothyroidism and chronic autoimmune thyroiditis in pregnancy among Italian and Romanian endocrinologists.

METHODS

Members of the Associazione Medici Endocrinologi (AME) and Romanian Society of Endocrinology (RSE) were invited to participate in a web-based survey investigating the topic.

RESULTS

A total of 902 individuals participated in the survey, 759 of whom completed all sections. Among the respondents, 85.1% were aware of the 2017 American Thyroid Association guidelines about thyroid disease and pregnancy, and 82.9% declared that thyroid-stimulating hormone (TSH) screening at the beginning of pregnancy should be warranted. In a patient negative for peroxidase antibodies, 53.6% considered 2.5 mIU/L and 26.2% considered 4.0 mIU/L as the upper normal limit of TSH, and 50% would treat a patient with TSH 3.5 mIU/L with levothyroxine. About 20% did not suggest iodine supplementation. Isolated hypothyroxinemia detected in the first trimester would be treated by 40.8%. In patients undergoing ovarian stimulation, a TSH < 2.5 mIU/L would be targeted by 70%.

CONCLUSIONS

Respondents globally appeared well informed about the management of thyroid autoimmunity and subclinical hypothyroidism in pregnancy. A more aggressive attitude in implementing iodine supplementation would be desirable. Most endocrinologists were convinced about an evident association between mild thyroid impairment and adverse outcomes in pregnancy, thus using a TSH value of 2.5 mIU/L as the threshold for diagnosing hypothyroidism and starting levothyroxine in pregnant women.

Thyroid Screening in Early Pregnancy: Pros and Cons

Universal thyroid screening in pregnancy is a key debate in thyroidology and obstetrics. It is well-established that thyroid hormones are essential for maintaining pregnancy and optimal fetal development. Thyroid dysfunction is common in women of child-bearing age and also results in substantial adverse obstetric and child neurodevelopmental outcomes. Furthermore, thyroid dysfunction is readily diagnosed with reliable blood tests and easily corrected with inexpensive and available treatments. Screening only high-risk patients appears to miss the majority of cases and economic models show that compared to high-risk screening, universal screening is cost effective even if only overt hypothyroidism was assumed to have adverse obstetric effects. As a result, several countries now implement universal screening. Opponents of universal thyroid screening argue that asymptomatic borderline thyroid abnormalities such as subclinical hypothyroidism and isolated hypothyroxinemia form the bulk of cases of thyroid dysfunction seen in pregnancy and that there is a lack of high quality evidence to support their screening and correction. This review critically appraises the literature, examines the pros and cons of universal thyroid screening using criteria laid down by Wilson and Jungner. It also highlights the growing evidence for universal thyroid screening and indicates the key challenges and practicalities of implementation.