Neurologic development of the newborn and young child in relation to maternal thyroid function

Lack of beneficiary effect of levothyroxine therapy of pregnant women with subclinical hypothyroidism in terms of neurodevelopment of their offspring

PURPOSE

Despite the beneficial effects of levothyroxine (LT4) therapy on pregnancy outcomes of women with subclinical hypothyroidism (SCH), its impact on the developmental status of offspring remains unclear. We aimed to assess the effects of LT4 therapy on the neurodevelopment of infants of SCH women in the first 3 years of life.

METHODS

A follow-up study was conducted on children born to SCH pregnant women who had participated in a single-blind randomized clinical trial (Tehran Thyroid and Pregnancy Study). In this follow-up study, 357 children of SCH mothers were randomly assigned to SCH + LT4 (treated with LT4 after the first prenatal visit and throughout pregnancy) and SCH-LT4 groups. Children born of euthyroid TPOAb-women served as the control group (n = 737). The neurodevelopment status of children was assessed in five domains (communication, gross motor, fine motor, problem-solving, and social-personal domains) using the Ages and Stages Questionnaires (ASQ) at the age of 3 years.

RESULTS

Pairwise comparisons of ASQ domains between euthyroid, SCH + LT4, and SCH-LT4 groups show no statistically significant difference between groups in the total score [median 25-75 total score: 265 (240-280); 270 (245-285); and 265 (245-285); P-value = 0.2, respectively]. The reanalyzing data using the TSH cutoff value of 4.0 mIU/L indicated no significant difference between groups in the score of ASQ in each domain or total score with TSH levels < 4.0 mIU/L, however, a statistically significant difference in the median score of the gross motor was observed between those SCH + LT4 with baseline TSH values ≥ 4.0 mIU/L and SCH-LT4 [60 (55-60) vs. 57.5 (50-60); P = 0.01].

CONCLUSIONS

Our study does not support the beneficiary effect of LT4 therapy for SCH pregnant women in terms of the neurological development of their offspring in the first three years of life.

Thyroid hormones regulate reelin expression in neuropsychiatric disorders

The incidence and prevalence of hypothyroidism in pregnancy have increased over the past two decades, leading to the occurrence of neuropsychiatric disorders. However, the underlying mechanisms of thyroid hormone (TH)-regulated gene expression and neuropsychiatric development during the postnatal period remain unknown. Recent achievements have shown that reelin, a large extracellular glycoprotein, plays a crucial role in neuronal migration and localization during the development of neocortex and cerebellar cortex, thereby participating in the development of neuropsychiatric diseases. Reelin-induced neuronal migration requires triiodothyronine (T3) from the deiodination of thyroxine (T4) by fetal brain deiodinases. Previous studies have reported decreased reelin levels and abnormal gene expression, which are the same as the pathological alternations in reelin-induced neuropsychiatric disorders including schizophrenia and autism. Low T3 in the fetal brain due to hypothyroxinemia during pregnancy may be detrimental to neuronal migration, leading to neuropsychiatric disorders. In this review, we focus on the reelin expression between hypothyroidism and neuropsychiatric disorders.

Preconception Counseling in Patients with Hypothyroidism and/or Thyroid Autoimmunity

Preconception counseling is an essential tool for preventing adverse pregnancy outcomes associated with thyroid dysfunction. The high prevalence of thyroid disease among women of reproductive age, and the increased risk of adverse pregnancy outcomes associated with thyroid dysfunction, emphasize the necessity for well-established screening and treatment criteria in the preconception period. We therefore conducted a literature review for relevant information on the screening, diagnosis and treatment of subclinical and overt hypothyroidism in women seeking pregnancy. While screening for thyroid disease is recommended only in the presence of risk factors, iodine supplementation should be recommended in most regions, with higher doses in areas with severe deficiency. Known hypothyroid women should be counseled about increasing their levothyroxine dose by 20–30% in the case of suspected or confirmed pregnancy (missed menstrual cycle or positive pregnancy test). Treating subclinical hypothyroidism appears to be beneficial, especially in the presence of autoimmunity or in patients undergoing artificial reproductive techniques. Regarding the management of TPOAb negative SCH women or euthyroid women with positive TPOAb, further research is necessary in order to make evidence-based recommendations.

Maternal Subclinical Hypothyroidism in Rats Impairs Spatial Learning and Memory in Offspring by Disrupting Balance of the TrkA/p75NTR Signal Pathway

Maternal subclinical hypothyroidism (SCH) during pregnancy can adversely affect the neurodevelopment of the offspring. The balance of nerve growth factor (NGF)-related tropomyosin receptor kinase A/p75 neurotrophin receptor (TrkA/p75^NTR) signaling in the hippocampus is important in brain development, and whether it affects cognitive function in maternal SCH’s offspring is not clear. In this study, we found that compared with the control (CON) group, expression of proliferation-related proteins [NGF, p-TrkA, phospho-extracellular signal-regulated kinase 1/2 (p-ERK1/2) and phospho-cAMP response element-binding protein (p-CREB)] decreased in the hippocampus of the offspring in the SCH group, overt hypothyroidism (OHT) group, and the group with levothyroxine (L-T₄) treatment for SCH from gestational day 17 (E17). In contrast, expression of apoptosis-related proteins [pro-NGF, p75^NTR, phospho-C-Jun N-terminal kinase (p-JNK), p53, Bax and cleaved caspase-3] was increased. The two groups with treatment with L-T₄ for SCH from E10 and E13, respectively, showed no significant difference compared with the CON group. L-T₄ treatment enhanced relative expression of NGF by increasing NGF/proNGF ratio in offspring from maternal SCH rats. In conclusion, L-T₄ treatment for SCH from early pregnancy dramatically ameliorated cognitive impairment via TrkA/p75^NTR signaling, which involved activation of the neuronal proliferation and inhibition of neuronal apoptosis in SCH rats’ offspring.

Thyroid function in neonates conceived after hysterosalpingography with iodinated contrast

STUDY QUESTION

Does exposure to preconceptional hysterosalpingography (HSG) with iodinated oil-based contrast affect neonatal thyroid function as compared to iodinated water-based contrast?

SUMMARY ANSWER

Preconceptional HSG with iodinated contrast did not influence the neonatal thyroid function.

WHAT IS KNOWN ALREADY

HSG is a commonly applied tubal patency test during fertility work-up in which either oil- or water-based contrast is used. Oil-based contrast contains more iodine compared to water-based contrast. A previous study in an East Asian population found an increased risk of congenital hypothyroidism (CH) in neonates whose mothers were exposed to high amounts of oil-based contrast during HSG.

STUDY DESIGN, SIZE, DURATION

This is a retrospective data analysis of the H2Oil study, a randomized controlled trial (RCT) comparing HSG with the use of oil- versus water-based contrast during fertility work-up. After an HSG with oil-based contrast, 214 women had an ongoing pregnancy within 6 months leading to a live birth compared to 155 women after HSG with water-based contrast.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Of the 369 women who had a live born infant, 208 consented to be approached for future research and 138 provided informed consent to collect data on the thyroid function tests of their offspring (n = 140). Thyroid function tests of these children were retrieved from the Dutch neonatal screening program, which includes the assessment of total thyroxine (T4) in all newborns, followed by thyroid-stimulating hormone only in those with a T4 level of ≤ -0.8 SD score. Furthermore, amount of contrast medium used and time between HSG and conception were compared between the two study groups.

MAIN RESULTS AND THE ROLE OF CHANCE

Data were collected from 140 neonates conceived after HSG with oil-based (n = 76) or water-based (n = 64) contrast. The median T4 concentration was 87.0 nmol/l [76.0-96.0] in the oil group and 90.0 nmol/l [78.0-106.0] in the water group (P = 0.13). None of the neonates had a positive screening result for CH.The median amount of contrast medium used was 9.0 ml [interquartile range (IQR), 6.0-11.8] in the oil-group and 10.0 ml [IQR, 7.5-14.0] in the water group (P = 0.43). No influence of the amount of contrast on the effect of contrast group on T4 concentrations was found (P-value for interaction, 0.37).

LIMITATIONS, REASONS FOR CAUTION

A relatively small sample size and possible attrition at follow-up are limitations of this study. Although our results suggest that the use of iodinated contrast media for HSG is safe for the offspring, the impact of a decrease in maternal thyroid function on offspring neurodevelopment could not be excluded, as data on maternal thyroid function after HSG and during conception were lacking.

WIDER IMPLICATIONS OF THE FINDINGS

As HSG with oil-based contrast does not affect thyroid function of the offspring, there is no reason to withhold this contrast to infertile women undergoing HSG. Future studies should investigate whether HSG with iodinated contrast influences the periconceptional maternal thyroid function and, consequently, offspring neurodevelopment.

STUDY FUNDING/COMPETING INTEREST(S)

This study received no funding. The original H2Oil RCT was an investigator-initiated study that was funded by the two academic institutions (Academic Medical Center and VU University Medical Center) of the Amsterdam UMC. The funders had no role in study design, collection, analysis and intrepretation of the data. I.R. reports receiving travel fee from Guerbet. C.B.L. reports speakers fee from Ferring in the past and research grants from Ferring, Merck and Guerbet. K.D. reports receiving travel fee and speakers fee from Guerbet. B.W.M. is supported by a NHMRC Practitioner Fellowship (GNT1082548). B.W.M. reports consultancy for ObsEva, Merck KGaA and Guerbet and travel and research grants from Merck KGaA and Guerbet. V.M. reports receiving travel fee and speakers fee as well as research grants from Guerbet. The other authors do not report conflicts of interest.

TRIAL REGISTRATION NUMBER

Netherlands Trial Register NTR 7526 (Neonates born after the H2Oil study), NTR 3270 (original H2Oil study), www.trialregister.nl.

Thyroid hormone replacement therapy in pregnancy and motor function, communication skills, and behavior of preschool children: The Norwegian Mother, Father, and Child Cohort Study

PURPOSE

Limited research has focused on the association between prenatal thyroid hormone replacement therapy (THRT) and motor function, communication skills, and behavior in preschool children. Here, we estimated the association between THRT during pregnancy and the first trimester and these developmental outcomes.

METHODS

This study was based on the Norwegian Mother, Father, and Child Cohort Study (MoBa) and other national registries. We included mother-child pairs exposed to THRT during pregnancy (n = 663), after delivery (n = 728), or unexposed (n = 28 040). Exposure to THRT was defined according to filled prescriptions. Child outcomes, presented as T-score differences, were parent-reported using the Ages and Stages Questionnaire, Strengths and Difficulties Questionnaire, and Child Behavior Checklist.

RESULTS

Of 29 431 mother-child pairs, 2.3% were prenatally exposed to THRT. We found no difference between prenatally exposed and unexposed children in regards to gross motor function (β: 0.17, 95% CI -1.19, 1.54), fine motor function (β: -0.17, 95% CI -1.14, 0.80), communication (β: -0.31, 95% CI -1.58, 0.96), externalizing (β: -0.03, 95% CI -1.07, 1.01), internalizing (β: 0.89, 95% CI -0.20, 1.97), or social behaviors (β: -0.04, 95% CI -0.92, 0.84). Somatic complaints were higher in THRT-exposed children (β: 0.98, 95% CI 0.08, 1.87), and children whose mothers were exposed after delivery had more sleep problems than unexposed children (β: 0.99, 95% CI 0.24, 1.74).

CONCLUSIONS

Children prenatally exposed to THRT have developmental outcomes as positive as unexposed children on motor function, communication, and behavior. The association with somatic complaints and sleep were not clinically relevant.

Biochemical and Ultrasound Characteristics of Subclinical Hypothyroid Patients in North of Jordan: Who Was Treated?

BACKGROUND

Early diagnosis and management of subclinical hypothyroidism (SCH) are important to avoid the risk of developing overt hypothyroidism. This study aimed to evaluate patients with subclinical hypothyroidism (SCH), in regard to their biochemical characteristics, and ultrasound features, and factors associated with initiating treatment for this condition.

METHODS

This was a retrospective study, which reviewed the data of patients who visited the Endocrinology clinic of a tertiary hospital in Jordan, King Abdullah University Hospital. Patients who visited the clinic with SCH over 1 year, Jan 2016-Dec 2016, were included. The charts were reviewed again 2 years later to check patients who started L-thyroxine for the different indications of treatment of SCH. Thyroid function tests (free T3, free T4, and TSH) and thyroid peroxidase antibodies (TPO-Ab) were found to be measured for all cases (n=287), among whom, thyroid ultrasound was done for 43 patients.

RESULTS

Most patients were females (88.1%). Mean age was 42.36 (±15.36 years). Positive TPO-Ab status was associated with higher TSH (p=0.056), lower free T4 levels (p= 0.012), and more patients treated with L- thyroxine for SCH in 2 years (p=0.001). On ultrasound, hypoechogenicity was more predominant among TPO-Ab positive patients than TPO-Ab negative patients (78% vs 30%).

CONCLUSION

SCH patients with positive TPO-Abs were more likely to be treated for this condition based on the various indications, and more likely to have had hypoechogenicity on ultrasound. Hence, thyroid ultrasonography and TPO-Ab status should be implemented early in evaluating and treating patients with SCH.

Systemic endocrinopathies (thyroid conditions and diabetes): impact on postnatal life of the offspring

Fetal programming may influence childhood and adult life, determining the risk of specific diseases. During earlier stages of pregnancy, the transfer of maternal thyroid hormones to the fetus is vital for adequate neurologic development. The presence of severe maternal thyroid dysfunction, particularly severe iodine deficiency, is devastating, leading to irreversible neurologic sequelae. Moreover, mild maternal thyroid conditions, such as a mild-to-moderate iodine deficiency, may also lead to milder neurologic and behavioral conditions later during the life of the offspring. Maternal dysglycemia due to pregestational or gestational diabetes mellitus is another common situation in which fetal development encounters a hostile environment. Hyperglycemia in utero may trigger metabolic conditions in the offspring, including abnormalities of glucose tolerance and weight excess. Physicians assisting pregnant women have to be aware about these conditions, because they may go unnoticed if not properly screened. Because an early diagnosis and appropriate management may prevent most of the possible negative consequences for the progeny, the prevention, early diagnosis, and proper management of these endocrine conditions should be offered to all women undergoing pregnancy. Here, we comprehensively review the current evidence about the effects of maternal thyroid dysfunction and maternal dysglycemia on the cognitive function and carbohydrate metabolism in the offspring, two prevalent conditions of utmost importance for the child's health and development.

Longitudinal analysis reveals early-pregnancy associations between perfluoroalkyl sulfonates and thyroid hormone status in a Canadian prospective birth cohort

Serum perfluoroalkyl acids (PFAAs) have been linked to disruption of maternal thyroid hormone homeostasis, but results have varied between studies which we hypothesized was due to timing of the thyroid hormone measurements, variability in PFAA isomer patterns, or presence of other stressors. In a longitudinal study design, we investigated the time-dependency of associations between PFAA isomers and thyroid hormones during pregnancy and post-partum while considering thyroid peroxidase antibody (TPOAb) status and mercury (Hg) co-exposure. In participants of a prospective Canadian birth cohort (n = 494), free thyroxine (FT4), free triiodothyronine (FT3), thyroid stimulating hormone (TSH) and TPOAb were quantified in maternal plasma collected in each trimester and 3-months postpartum, and 25 PFAAs (15 linear and 10 branched) and Hg were quantified in samples collected during the second trimester. Perfluorohexane sulfonate (PFHxS) and total branched isomers of perfluorooctane sulfonate (PFOS) were positively associated with TSH in mixed-effect models, with strongest associations early in gestation. Throughout pregnancy and post-partum, PFHxS was inversely associated with FT4, consistent with elevated TSH, while Hg was inversely associated with FT3. In TPOAb-positive women, negative associations were found between PFUnA and FT4, and 1m-PFOS and TSH, supporting previous studies that thyroid disorder could increase susceptibility to PFAA-mediated hormone dysregulation. Hg did not confound associations but was a significant interaction term, revealing further positive associations between PFOS isomers (∑3m+4m-PFOS) and TSH. Higher perfluoroalkyl sulfonate exposures were associated with higher TSH and/or lower FT4, strongly suggestive that PFHxS and branched PFOS isomers are risk factors for subclinical maternal hypothyroidism. Isomer-specific analysis is important in future studies, as crude measures of 'total-PFOS' masked the associations of branched isomers. A concerning result was for PFHxS which had consistent negative associations with FT4 at all time points and a positive association with TSH in early pregnancy when fetal development is most sensitive to disruption.

Fluoride Exposure Induces Inhibition of Sodium-and Potassium-Activated Adenosine Triphosphatase (Na+, K+-ATPase) Enzyme Activity: Molecular Mechanisms and Implications for Public Health

In this study, several lines of evidence are provided to show that Na + , K + -ATPase activity exerts vital roles in normal brain development and function and that loss of enzyme activity is implicated in neurodevelopmental, neuropsychiatric and neurodegenerative disorders, as well as increased risk of cancer, metabolic, pulmonary and cardiovascular disease. Evidence is presented to show that fluoride (F) inhibits Na + , K + -ATPase activity by altering biological pathways through modifying the expression of genes and the activity of glycolytic enzymes, metalloenzymes, hormones, proteins, neuropeptides and cytokines, as well as biological interface interactions that rely on the bioavailability of chemical elements magnesium and manganese to modulate ATP and Na + , K + -ATPase enzyme activity. Taken together, the findings of this study provide unprecedented insights into the molecular mechanisms and biological pathways by which F inhibits Na + , K + -ATPase activity and contributes to the etiology and pathophysiology of diseases associated with impairment of this essential enzyme. Moreover, the findings of this study further suggest that there are windows of susceptibility over the life course where chronic F exposure in pregnancy and early infancy may impair Na + , K + -ATPase activity with both short- and long-term implications for disease and inequalities in health. These findings would warrant considerable attention and potential intervention, not to mention additional research on the potential effects of F intake in contributing to chronic disease.

Maternal hypothyroidism and future pediatric neurological morbidity of the offspring

BACKGROUND

Maternal hypothyroidism in pregnancy has been associated with neurocognitive impairment in exposed children, ranging from psychomotor-developmental delay to lower IQ scores.

OBJECTIVE

To investigate the long-term neurological morbidity of children to hypothyroid mothers during pregnancy.

STUDY DESIGN

A population-based cohort study was performed including all deliveries occurring in a period of 20 years at a tertiary medical center. We excluded multiple pregnancies, fetuses with congenital malformations, perinatal mortality cases and women lacking prenatal care from the study. Neurological-related hospitalizations of children (up to 18 years) were evaluated using neurological morbidities that were predefined by ICD-9 codes. Kaplan-Meier survival curve was used to compare cumulative hospitalization rate in exposed and unexposed children. A Cox regression model was used to control for confounders.

RESULTS

During the study period, 217,910 deliveries met the inclusion criteria. Of them, 1.1% (n = 2403) were in mothers with known hypothyroidism during pregnancy. The Kaplan-Meier survival curve demonstrated a significantly higher cumulative incidence of neurological-related hospitalizations in the hypothyroidism group (log rank p = 0.007). Total hospitalization rate per person years was significantly higher in the maternal hypothyroidism group (5.5 vs. 3.1, HR =1.37, 95% CI 1.10-1.73, p = 0.007). The Cox regression model controlled for various possible confounders including maternal age, maternal obesity, birth weight, preterm birth, maternal diabetes, hypertensive disorders, induction of labor and mode of delivery, found maternal hypothyroidism to be independently associated with pediatric neurological morbidity in these children (adjusted HR =1.33, 95% CI 1.05-1.68, p = 0.01).

CONCLUSION

Maternal hypothyroidism in pregnancy is independently associated with long-term pediatric neurological morbidity of the offspring.

Evaluation of the impact of levothyroxine treatment on the psychomotor developmental status of three-year-old children born to mothers with mild thyroid impairment; Tehran Thyroid and pregnancy study: study protocol for a randomized clinical trial

Background

Despite the known adverse effects of maternal overt hypothyroidism on the neurocognitive development of children, there is uncertainty regarding the impact of gestational thyroid dysfunction or autoimmune thyroiditis on infant/child neurological development. This study aims to evaluate the impact of levothyroxine (LT4) treatment on the psychomotor developmental status of three-year-old children born to mothers with mild thyroid impairment (subclinical hypothyroidismwith/without autoimmune thyroiditis).

Methods/Design

This is a follow-up study of the Tehran Thyroid and Pregnancy Study, a randomized trial in which subclinical hypothyroid pregnant women were assigned to an intervention group (treated with levothyroxine) or a control group (received no treatment). The primary outcome for the purpose of the present study is the developmental status of the children, aged three years, in five domains (communication, gross motor, fine motor, problem-solving, and social–personal domains) using the Ages and Stages Questionnaire (ASQ).

Discussion

The study is designed to assess the developmental status of children born to mothers with mild thyroid impairment (subclinical hypothyroidism with/without autoimmune thyroiditis). This study is one of the limited studies available in this field and has the potential to facilitate much-needed information for related public health policies.

Trial registration

Iranian Registry of Clinical Trials, IRCT2017090314849N5. Registered on 11 September 2017. Iranian Registry of Clinical Trials, IRCT2017090414849N6. Registered on 14 October 2017.

Electronic supplementary material

The online version of this article (10.1186/s13063-018-3130-5) contains supplementary material, which is available to authorized users.

Thyroid function and thyroid disorders during pregnancy: a review and care pathway

PURPOSE

To review the literature on thyroid function and thyroid disorders during pregnancy.

METHODS

A detailed literature research on MEDLINE, Cochrane library, EMBASE, NLH, ClinicalTrials.gov, and Google Scholar databases was done up to January 2018 with restriction to English language about articles regarding thyroid diseases and pregnancy.

RESULTS

Thyroid hormone deficiencies are known to be detrimental for the development of the fetus. In particular, the function of the central nervous system might be impaired, causing low intelligence quotient, and mental retardation. Overt and subclinical dysfunctions of the thyroid disease should be treated appropriately in pregnancy, aiming to maintain euthyroidism. Thyroxine (T4) replacement therapy should reduce thyrotropin (TSH) concentration to the recently suggested fixed upper limits of 2.5 mU/l (first and second trimester) and 3.0 mU/l (third trimester). Overt hyperthyroidism during pregnancy is relatively uncommon but needs prompt treatment due to the increased risk of preterm delivery, congenital malformations, and fetal death. The use of antithyroid drug (methimazole, propylthiouracil, carbimazole) is the first choice for treating overt hyperthyroidism, although they are not free of side effects. Subclinical hyperthyroidism tends to be asymptomatic and no pharmacological treatment is usually needed. Gestational transient hyperthyroidism is a self-limited non-autoimmune form of hyperthyroidism with negative antibody against TSH receptors, that is related to hCG-induced thyroid hormone secretion. The vast majority of these patients does not require antithyroid therapy, although administration of low doses of β-blocker may by useful in very symptomatic patients.

CONCLUSIONS

Normal maternal thyroid function is essential in pregnancy to avoid adverse maternal and fetal outcomes.

Hypothyroidism during pregnancy: Controversy over screening and intervention

Thyroid hormones are critical for foetal neurological development and maternal health. Maternal hypothyroidism during pregnancy is associated with adverse impact on health of the mother as well as the progeny. Reduced thyroid hormone levels predispose the child to develop mental retardation and cognitive delay in early life. In the mother, hypothyroidism during pregnancy is associated with spontaneous abortion, placental abruption, preterm delivery and hypertensive disorders. Therefore, screening and therapeutic intervention is justified to prevent foetal as well as maternal co-morbidities. In view of impact of such a large-scale screening and intervention program on limited healthcare resources, it is debatable if a targeted rather than universal screening program will result in comparable outcomes. In addition, there is an ongoing debate regarding best evidence-based practice for the management of isolated hypothyroxinaemia, subclinical hypothyroidism and euthyroid women with autoimmune hypothyroidism. We have carried out a review of the literature; firstly, to determine whether universal screening for asymptomatic women in early pregnancy would be cost-effective. Secondly, we have retrospectively reviewed the literature to analyse the evidence regarding the impact of therapeutic intervention in women with subclinical hypothyroidism.

Subclinical Hypothyroidism in Women Planning Conception and During Pregnancy: Who Should Be Treated and How?

Subclinical hypothyroidism (SCH), a mild form of hypothyroidism defined as elevated TSH with normal free thyroxine levels, is a common diagnosis among women of reproductive age. In some, but not all, studies, it has been associated with infertility, an increased risk of adverse pregnancy and neonatal outcomes, and possibly with an increased risk of neurocognitive deficits in offspring. Despite well-established recommendations on treatment of overt hypothyroid pregnant women, a consensus has not yet been reached on whether to treat women with SCH. This review focuses on examining the evidence informing the clinical strategy for using levothyroxine (LT4) in women with SCH during pregnancy and those who are planning conception. A crucial first step is to accurately diagnose SCH using the appropriate population-based reference range. For pregnant women, if this is unavailable, the recommended TSH upper normal limit cutoff is 4.0 mIU/L. There is evidence supporting a decreased risk for pregnancy loss and preterm delivery for pregnant women with TSH > 4.0 mIU/L receiving LT4 therapy. LT4 treatment has been associated with better reproductive outcomes in women with SCH undergoing artificial reproductive techniques, but not in those who are attempting natural conception. Thyroid function tests need to be repeated throughout pregnancy to monitor LT4 therapy. In addition to potential harms, LT4 contributes to treatment burden. During a consultation, clinicians and patients should engage in a careful consideration of the current evidence in the context of the patients’ values and preferences to determine whether LT4 therapy initiation is the best next step.

Developmental milestones at one year for the offspring of mothers with congenital hypothyroidism: a population-based study

OBJECTIVE

Maternal thyroid dysfunction during pregnancy is associated with neurodevelopmental impairment in the offspring. No data are currently available for the offspring of patients treated early for congenital hypothyroidism (CH). The aim of this study was to investigate motor and language milestones at one year of age in a population-based registry of children born to young women with CH.

DESIGN AND METHODS

We assessed 110 children born to mothers with CH, and 1367 children from the EDEN French population-based birth cohort study prospectively, at the age of one year, with identical questionnaires. Outcomes were assessed in terms of scores for childhood developmental milestones relating to mobility, motor coordination, communication, motricity and language skills.

RESULTS

After adjustment for confounding factors, children born to mothers with CH were found to have a higher risk of poor motor coordination than those of the EDEN cohort (OR: 4.18, 95% CI: 2.52-6.93). No differences were identified for the other four domains investigated. Children born to mothers with gestational diabetes have a higher risk of low motor coordination score than their peers (OR: 2.10, 95% CI: 1.21-3.66). Children born to mothers with TSH ≥ 10 IU/L during the first six months of pregnancy were more likely to have low motricity or communication skills scores than those born to mothers with lower TSH concentrations (56% vs 21% for each score, P < 0.04).

CONCLUSIONS

Maternal CH may have slight adverse effects on some developmental milestones in the child at one year of age, particularly for children born to mothers with uncontrolled hypothyroidism. However, it remains unclear whether these adverse effects modify subsequent neurodevelopment.

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.

Controlled Antenatal Thyroid Screening II: Effect of Treating Maternal Suboptimal Thyroid Function on Child Cognition

CONTEXT AND OBJECTIVE

The Controlled Antenatal Thyroid Screening (CATS) study investigated treatment of suboptimal gestational thyroid function (SGTF) on childhood cognition and found no difference in intelligence quotient (IQ) at 3 years between children of treated and untreated SGTF mothers. We have measured IQ in the same children at age 9.5 years and included children from normal gestational thyroid function (normal-GTF) mothers.

DESIGN, SETTING, AND PARTICIPANTS

One examiner, blinded to participant group, assessed children's IQ (Wechsler Intelligence Scale for Children, Fourth Edition UK), long-term memory, and motor function (Developmental Neuropsychological Assessment II) from children of 119 treated and 98 untreated SGTF mothers plus children of 232 mothers with normal-GTF. Logistic regression explored the odds and percentages of an IQ < 85 in the groups.

RESULTS

There was no difference in IQ < 85 between children of mothers with normal-GTF and combined SGTF, i.e., treated and untreated (fully adjusted odds ratio [OR] = 1.15 [95% confidence interval (CI) 0.52, 2.51]; P = 0.731). Furthermore, there was no significant effect of treatment [untreated OR = 1.33 (95% CI 0.53, 3.34); treated OR = 0.75 (95% CI 0.27, 2.06) P = 0.576]. IQ < 85 was 6.03% in normal-GTF, 7.56% in treated, and 11.22% in untreated groups. Analyses accounting for treated-SGTF women with free thyroxine > 97.5th percentile of the entire CATS-I cohort revealed no significant effect on a child's IQ < 85 in CATS-II. IQ at age 3 predicted IQ at age 9.5 (P < 0.0001) and accounted for 45% of the variation.

CONCLUSIONS

Maternal thyroxine during pregnancy did not improve child cognition at age 9.5 years. Our findings confirmed CATS-I and suggest that the lack of treatment effect may be a result of the similar proportion of IQ < 85 in children of women with normal-GTF and SGTF.

Maternal hypothyroxinaemia in early pregnancy and problem behavior in 5-year-old offspring

INTRODUCTION

There is evidence, though not consistent, that offspring born to mothers with subtle decreases in thyroid function early in their pregnancies may be at risk of cognitive impairments and attention problems. However, other types of problem behavior have not been addressed thus far. We tested whether maternal thyroid function in early pregnancy is associated with several types of problem behavior in offspring at age 5-6 years.

METHODS

This was a longitudinal study that included the data of 2000 mother-child pairs from the Amsterdam Born Children and their Development study. At a median gestational age of 12.9 (interquartile range: 11.9-14.1) weeks, maternal blood was sampled for assessment of free T4 and TSH. Overall problem behavior, hyperactivity/inattention, conduct problems, emotional problems, peer relationship problems and prosocial behavior were measured at age 5-6 years using the Strengths and Difficulties Questionnaire, which was filled out by both parents and teachers.

RESULTS

Maternal hypothyroxinaemia <5th percentile was associated with a 1.70 (95% confidence interval (CI): 1.01-2.86) increased odds of teacher-reported hyperactivity/inattention after adjustment for confounders. By increasing the cut-off level to <10th percentile, the odds ratio became 1.47 (95% CI: 0.99-2.20). There were no associations between maternal thyroid function parameters and hyperactivity/inattention as reported by parents, nor with teacher or parent reports of other types of problem behavior.

CONCLUSIONS

Our results partially confirm previous observations, showing that early disruptions in the maternal thyroid hormone supply may be associated with ADHD symptoms in offspring. Our study adds that there is no evidence for an effect on other types of problem behavior.

Management of Neonates Born to Mothers With Graves' Disease

Neonates born to mothers with Graves' disease are at risk for significant morbidity and mortality and need to be appropriately identified and managed. Because no consensus guidelines regarding the treatment of these newborns exist, we sought to generate a literature-based management algorithm. The suggestions include the following: (1) Base initial risk assessment on maternal thyroid stimulating hormone (TSH) receptor antibodies. If levels are negative, no specific neonatal follow-up is necessary; if unavailable or positive, regard the newborn as "at risk" for the development of hyperthyroidism. (2) Determine levels of TSH-receptor antibodies in cord blood, or as soon as possible thereafter, so that newborns with negative antibodies can be discharged from follow-up. (3) Measurement of cord TSH and fT4 levels is not indicated. (4) Perform fT4 and TSH levels at day 3 to 5 of life, repeat at day 10 to 14 of life and follow clinically until 2 to 3 months of life. (5) Use the same testing schedule in neonates born to mothers with treated or untreated Graves' disease. (6) When warranted, use methimazole (MMI) as the treatment of choice; β-blockers can be added for sympathetic hyperactivity. In refractory cases, potassium iodide may be used in conjunction with MMI. The need for treatment of asymptomatic infants with biochemical hyperthyroidism is uncertain. (7) Assess the MMI-treated newborn on a weekly basis until stable, then every 1 to 2 weeks, with a decrease of MMI (and other medications) as tolerated. MMI treatment duration is most commonly 1 to 2 months. (8) Be cognizant that central or primary hypothyroidism can occur in these newborns.

The impact of thyroid abnormalities during pregnancy on subsequent neuropsychological development of the offspring: a meta-analysis

OBJECTIVE

To investigate the relationship between specific thyroid abnormalities in women during pregnancy and the subsequent neuropsychological development of their offspring.

METHODS

A systematic literature search of PubMed, Embase and Web of Science was conducted. Eligible studies were case-control or cohort study that explored this association with euthyroid thyroid abnormalities during pregnancy. The outcomes included intelligence scores and motor scores. Weighted mean differences (WMDs) and 95% confidence intervals (CIs) were calculated and heterogeneity was assessed with Cochrane Q chi-square test and I(2) statistics. A fixed-effects or random-effects model was used to pool the estimates according to the heterogeneity among the included studies.

RESULTS

Six studies, involving 4449 participants, were included. Children of women with thyroid abnormalities had mean intelligence score of 6.27 points and motor score of 5.99 points lower than that of children of euthyroid women. Subgroup analysis suggested that, children of women with hypothyroxinaemia, subclinical hypothyroidism and positive TPOAb had mean intelligence scores of 5.69 points, 8.76 points and 10.55 points, and mean motor scores of 4.19 points, 9.98 points and 9.03 points lower than those of the controls, respectively.

CONCLUSIONS

The thyroid abnormalities in pregnant women may adversely affect neuropsychological development of their offspring.

Maternal and Child's Thyroid Function and Child's Intellect and Scholastic Performance

BACKGROUND

Maternal hypothyroidism and/or hypothyroxinemia have been associated with child's poor neuropsychological development, but the results have been inconsistent.

METHODS

The Northern Finland Birth Cohort 1986 included all expected births within a year (9362 women, 9479 children) from the two northernmost provinces of Finland. Maternal serum samples (n = 5791) were obtained in early pregnancy (M ± SD = 10.7 ± 2.8 weeks' gestation), and serum samples from their children were obtained at 16 years of age (n = 5829). All samples were analyzed for thyrotropin, free thyroxine (fT4), and thyroid peroxidase antibodies. The children's school performance was evaluated by their main teachers at eight years of age, as well as by the adolescents themselves at 16 years of age. Data on possible severe intellectual deficiency and mild cognitive limitation were collected from healthcare records and registries for all children. Logistic regression estimated the odds of poor school performance or severe intellectual deficiency/mild cognitive limitation associated with exposure to maternal thyroid dysfunction. The odds of poor school performance associated with the adolescents' own thyroid function at age 16 were also estimated. Results are presented as odds ratios (OR) with confidence intervals (CI), adjusted for maternal/family covariates and child's sex.

RESULTS

Girls of mothers with subclinical hypothyroidism had more self-evaluated difficulties in mathematics than did girls of euthyroid mothers (OR 1.62 [CI 1.06-2.49]). Boys of hypothyroxinemic mothers repeated a school class more often than did boys of euthyroid mothers (OR 5.46 [CI 1.19-25.06]). Adolescents of hyperthyroid mothers had increased odds of poor self-evaluated performance in mathematics (OR 1.61 [CI 1.01-2.49]). Maternal thyroid dysfunction did not increase the odds of a child having severe intellectual deficiency/mild cognitive limitation. At 16 years of age, girls with hyperthyroidism by laboratory measurements had more difficulties in Finnish language (OR 2.82 [CI 1.42-5.61]) than did euthyroid girls. Boys with hypothyroxinemia by laboratory measurement had higher odds of having difficulties in Finnish and/or mathematics (OR 2.13 [CI 1.26-3.62]) than did euthyroid boys.

CONCLUSIONS

Maternal thyroid dysfunction during early pregnancy was associated with poorer scholastic performance of the adolescent. Additionally, adolescents' own thyroid dysfunction was associated with difficulties in school performance assessed by self-evaluation.

The second wave of the Controlled Antenatal Thyroid Screening (CATS II) study: the cognitive assessment protocol

BACKGROUND

Children whose mothers had low thyroid hormone levels during pregnancy have been reported to have decreased cognitive function. The reported research is part of the follow-on study of the Controlled Antenatal Thyroid Screening Study (CATS I), a randomised controlled trial which investigated the impact of treated vs. untreated low thyroid hormone level in women during pregnancy with the primary outcome being the child's IQ at age 3. No significant differences in IQ were found between the treated and untreated groups. These children are now aged between 7 and 10 years and aspects of their cognitive functioning including their IQ are being reassessed as part of CATS II.

METHODS/DESIGN

Cognitive assessments generate an IQ score and further tests administered will investigate long term memory function and motor coordination. The aim is to complete the assessments with 40% of the children born to mothers either in the treated or untreated low thyroid hormone groups (n = 120 per group). Also children born to mothers who had normal thyroid functioning during CATS I are being assessed for the first time (n = 240) to provide a comparison. Assessments are conducted either in the research facility or the participant's home.

DISCUSSION

The study is designed to assess the cognitive functioning of children born to mothers with low thyroid hormone levels and normal thyroid functioning during pregnancy. This is the largest study of its type and also is distinguishable in its longitudinal design. The research has the potential to have a significant impact on public health policy in the UK; universal screening of thyroid hormone levels in pregnancy may be the recommendation.

Effects of maternal hypothyroidism on offspring hippocampus and memory

BACKGROUND

Rodents with gestational thyroid-hormone (TH) deficiencies and children with congenital hypothyroidism show abnormal hippocampal development. Given that the human hippocampus starts to develop early in gestation, we asked if children born to women with hypothyroidism during pregnancy also show hippocampal abnormalities and if this is related to the severity of maternal TH insufficiency and current memory functioning. We additionally sought to determine whether effects were more prominent in anterior or posterior hippocampal subsections given these support different memory functions and have different developmental trajectories. We hypothesized that these children would have smaller than normal hippocampal volumes than controls and show memory deficits on both standardized tests and indices of "everyday" memory functioning.

METHODS

We studied 54 children aged 9 to 12 years: 30 controls and 24 HYPO cases-offspring from women diagnosed with hypothyroidism prior to or during pregnancy and treated with l-thyroxine. All children received a thorough assessment of memory functions and an MRI scan. For each child, right and left hippocampi were manually traced, and volumes of right and left hippocampi and anterior and posterior segments were determined.

RESULTS

HYPO cases showed significantly smaller right and left hippocampal volumes than controls, particularly in right posterior and left anterior segments. In HYPO children, hippocampal volumes were negatively correlated with maternal third-trimester TSH levels and positively correlated with third-trimester fT4. HYPO cases scored significantly below controls on one objective and several subjective memory indices, and these were correlated with hippocampal volumes.

CONCLUSION

Early TH insufficiency from maternal hypothyroidism affects offspring hippocampal development and memory.

The Na+/I- symporter (NIS): mechanism and medical impact

The Na(+)/I(-) symporter (NIS) is the plasma membrane glycoprotein that mediates active I(-) transport in the thyroid and other tissues, such as salivary glands, stomach, lactating breast, and small intestine. In the thyroid, NIS-mediated I(-) uptake plays a key role as the first step in the biosynthesis of the thyroid hormones, of which iodine is an essential constituent. These hormones are crucial for the development of the central nervous system and the lungs in the fetus and the newborn and for intermediary metabolism at all ages. Since the cloning of NIS in 1996, NIS research has become a major field of inquiry, with considerable impact on many basic and translational areas. In this article, we review the most recent findings on NIS, I(-) homeostasis, and related topics and place them in historical context. Among many other issues, we discuss the current outlook on iodide deficiency disorders, the present stage of understanding of the structure/function properties of NIS, information gleaned from the characterization of I(-) transport deficiency-causing NIS mutations, insights derived from the newly reported crystal structures of prokaryotic transporters and 3-dimensional homology modeling, and the novel discovery that NIS transports different substrates with different stoichiometries. A review of NIS regulatory mechanisms is provided, including a newly discovered one involving a K(+) channel that is required for NIS function in the thyroid. We also cover current and potential clinical applications of NIS, such as its central role in the treatment of thyroid cancer, its promising use as a reporter gene in imaging and diagnostic procedures, and the latest studies on NIS gene transfer aimed at extending radioiodide treatment to extrathyroidal cancers, including those involving specially engineered NIS molecules.

Adequate levothyroxine doses for the treatment of hypothyroidism newly discovered during pregnancy

BACKGROUND

Recent guidelines recommend thyrotropin (TSH) target levels of ≤2.5 mIU/L for the first trimester and ≤3 mIU/L for the subsequent trimesters. Euthyroidism should be attained as soon as possible, but there are no precise indications about the initial levothyrorine (LT4) dose. The aim of our study was to determine the appropriate LT4 doses in order to normalize TSH levels in patients with newly discovered subclinical hypothyroidism (SCH) during pregnancy, and to correlate them with basal TSH levels. The adequate LT4 doses for women with SCH were also compared to those required in pregnant women with overt hypothyroidism (OH).

METHODS

Seventy-seven patients with newly diagnosed hypothyroidism during pregnancy were retrospectively analyzed. Patients were assigned to group 1 (n = 64) with SCH or group 2 (n = 13) with OH. SCH patients were subdivided into two groups: group 1a serum TSH >2.5 (1st trimester) or >3 (2nd or 3rd trimester) to 4.2 mIU/L; and group 1b TSH level > 4.21-10 mIU/L. All patients were treated with LT4 as soon as hypothyroidism was diagnosed. The dose that allowed a TSH of ≤2.5 mIU/L to be reached in the first trimester or one that allowed a TSH of ≤3 mIU/L to be reached during the second and third trimesters was considered the appropriate one.

RESULTS

A significant difference (p < 0.0001) in the appropriate LT4 dose (mean ± SD, μg/kg/day) was observed between group 1 and group 2: 1.31 ± 0.36 versus 2.33 ± 0.59. Patients in group 1a required a significantly lower LT4 dose (p < 0.014) than group1b: 1.20 ± 0.39 versus 1.42 ± 0.31 μg/kg/day. In 57 of the 64 (89.06%) women with SCH and in 10/13 (76.92%) women with OH, the appropriate LT4 dose coincided with the initial dose. Only 11% and 23% respectively required additional adjustments. Once the appropriate dose of LT4 was prescribed, the time at which euthyroidism (mean ± SD, weeks) was confirmed was similar in patients with SCH (6.06 ± 3.3) and OH (5.3 ± 1.8). There were no miscarriages or premature deliveries.

CONCLUSIONS

When hypothyroidism is newly discovered during pregnancy, we suggest initiating the treatment with the following LT4 doses: 1.20 μg/kg/day for SCH with TSH ≤ 4.2  mIU/L, 1.42 μg/kg/day with TSH > 4.2-10, and 2.33 μg/kg/day for OH. By taking this approach, patients will promptly attain the euthyroid state avoiding additional increments and, probably, obstetric risks.

Iodine and mental development of children 5 years old and under: a systematic review and meta-analysis

Several reviews and meta-analyses have examined the effects of iodine on mental development. None focused on young children, so they were incomplete in summarizing the effects on this important age group. The current systematic review therefore examined the relationship between iodine and mental development of children 5 years old and under. A systematic review of articles using Medline (1980-November 2011) was carried out. We organized studies according to four designs: (1) randomized controlled trial with iodine supplementation of mothers; (2) non-randomized trial with iodine supplementation of mothers and/or infants; (3) prospective cohort study stratified by pregnant women's iodine status; (4) prospective cohort study stratified by newborn iodine status. Average effect sizes for these four designs were 0.68 (2 RCT studies), 0.46 (8 non-RCT studies), 0.52 (9 cohort stratified by mothers' iodine status), and 0.54 (4 cohort stratified by infants' iodine status). This translates into 6.9 to 10.2 IQ points lower in iodine deficient children compared with iodine replete children. Thus, regardless of study design, iodine deficiency had a substantial impact on mental development. Methodological concerns included weak study designs, the omission of important confounders, small sample sizes, the lack of cluster analyses, and the lack of separate analyses of verbal and non-verbal subtests. Quantifying more precisely the contribution of iodine deficiency to delayed mental development in young children requires more well-designed randomized controlled trials, including ones on the role of iodized salt.

Maternal hypothyroxinemia in early pregnancy predicts reduced performance in reaction time tests in 5- to 6-year-old offspring

CONTEXT

Overt hypothyroidism in pregnant women is associated with poorer neurodevelopment in their children. Findings from studies investigating the effect of less severe impairments in the maternal thyroid function on cognitive functioning in offspring are difficult to interpret for a number of reasons, including lack of objective cognitive tests, preschool age at assessment, and small sample sizes.

OBJECTIVE

We aimed to assess the effect of the maternal thyroid status in early pregnancy on their offspring's cognitive performance at 5 to 6 years of age.

DESIGN AND PARTICIPANTS

This was a prospective study that included the data of 1765 healthy 5- to 6-year-old children from the Amsterdam Born Children and their Development study. Maternal serum free T4 and TSH were obtained at a median gestational age of 90 (interquartile range, 83 to 100) days.

MAIN OUTCOME MEASURES

Cognitive performance was tested using a computerized assessment program that measured response speed, response speed stability, visuomotor skills, response selection, and response inhibition.

RESULTS

Maternal hypothyroxinemia (ie, maternal free T4 in the lowest 10% of distribution) was associated with a 41.3 (95% confidence interval, 20.3-62.4) ms slower response speed in a simple reaction time task. In this test, it was also associated with a decreased stability in response speed. The relations found persisted after adjustment for family background and perinatal conditions. The effect of hypothyroxinemia on these outcomes was dependent on its interaction with TSH level.

CONCLUSIONS

Lower maternal free T4 concentration at the end of the first trimester predicted slower response speed and decreased stability in response speed in offspring at 5 to 6 years of age.

Maternal and umbilical cord levels of T4, FT4, TSH, TPOAb, and TgAb in term infants and neurodevelopmental outcome at 5.5 years

CONTEXT

Relatively little is known in euthyroid populations about the changes in maternal thyroid hormones during pregnancy, the nature of the relationship to cord thyroid hormone levels, and subsequent infant neurodevelopment.

OBJECTIVES

The aim of the study was to describe the relationship between maternal and cord thyroid hormone parameters and to describe their associations with neurodevelopment at 5.5 years.

DESIGN

We conducted a follow-up of women and their children born at or over 37 weeks' gestation.

MAIN OUTCOMES

We measured maternal levels of TSH, thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), T(4), and free T(4) (FT(4)) at 10 and 34 weeks and at delivery, and cord levels of T(4), FT(4), TPOAb, and TgAb. The association of cord thyroid hormone parameters with McCarthy scale scores adjusted for the major confounders of neurodevelopment.

RESULTS

Fifteen percent of the women were TPOAb-positive, and 12% were TgAb-positive; the proportion of women with mildly elevated TSH levels increased during pregnancy with the maximum (14%) at delivery. Lower perceptual performance and motor scores were found with TgAb-positive women and lower perceptual performance scores with TgAb-positive cord levels; otherwise, unadjusted maternal levels of TPOAb, TgAb, and TSH and unadjusted cord levels of FT(4), TPOAb, and TgAb were not associated with neurodevelopment at 5.5 years. Low cord T(4) levels were associated with significant increments in four McCarthy scales: General Cognitive Index, Verbal, Quantitative, and Memory scales-increments that persisted after adjustment at 11.4, 7.8, 7.6, and 7.8 points, respectively.

CONCLUSIONS

Lower levels of cord T(4) were associated with increments in the McCarthy scales in the domains that tested cognitive and verbal abilities at 5.5 years.

Circulating maternal perfluoroalkyl substances during pregnancy in the C8 Health Study

Perfluoroalkyl substances are manmade chemicals used in many consumer products and have become ubiquitous in the environment. Animal studies and a limited number of human studies have demonstrated developmental effects in offspring exposed to perfluoroalkyl substances in utero, but the implications of timing of in utero exposure have not been systematically investigated. The present study investigated variation in perfluorocarbon levels of 9952 women of childbearing age who had been exposed to perfluorooctanoic acid (PFOA) in drinking water contaminated by industrial waste. An analysis of variance with contrast was performed to compare the levels of PFOA and perfluorooctanesulfonic acid (PFOS) in pregnant and nonpregnant women overall and during each trimester of pregnancy. We found that pregnant women had lower circulating PFOA and PFOS concentrations in peripheral blood than nonpregnant women and that PFOA levels were consistently lower throughout all trimesters for pregnancy, suggesting transfer to the fetus at an early stage of gestation. These results are discussed in the context of the endocrine-disrupting properties of perfluoroalkyl substances that have been characterized in animal and human studies. Our conclusion is that further, systematic study of the potential implications of intrauterine perfluorocarbon exposure during critical periods of fetal development is urgently needed.

The expanding role of tandem mass spectrometry in optimizing diagnosis and treatment of thyroid disease

This review discusses the state-of-the-art measurement of free and total thyroid hormones in clinical laboratories. We highlight some of the limitations of currently used immunoassays and critically discuss physical separation methods for the measurement of free thyroid hormone. Physical separation methods, such as equilibrium dialysis or ultrafiltration, followed by tandem mass spectrometry for the measurement of free thyroid hormones offer many advantages, which we feel, can deepen our understanding of thyroid hormone metabolism and improve patient diagnosis and care. Problems with direct analogue immunoassay methods for FT4/FT3 as well as immunoassay methods for total T3 at low T3 concentrations and during pregnancy are highlighted. Improved diagnosis and patient management can be achieved utilizing tandem mass spectrometry for these measurements.

Thyroid dysfunction and autoantibodies association with hypertensive disorders during pregnancy

Background. Thyroid dysfunction and autoimmunity are relatively common in reproductive age and have been associated with adverse health outcomes for both mother and child, including hypertensive disorders during pregnancy. Objective. To survey the relation between thyroid dysfunction and autoimmunity and incidence and severity of pregnancy-induced hypertensive disorders. Method. In this case control study 48 hypertensive patients in 4 subgroups (gestational hypertension, mild preeclampsia, severe preeclampsia, eclampsia) and 50 normotensive ones were studied. The samples were nulliparous and matched based on age and gestational age and none of them had previous history of hypertensive or thyroid disorders and other underlying systemic diseases or took medication that might affect thyroid function. Their venous blood samples were collected using electrochemiluminescence and ELISA method and thyroid hormones and TSH and autoantibodies were measured. Results. Hypertensive patients had significant lower T3 concentration compared with normotensive ones with mean T3 values 152.5 ± 48.93 ng/dL, 175.36 ± 58.07 ng/dL respectively. Anti-TPO concentration is higher in control group 6.07 ± 9.02 IU/mL compared with 2.27 ± 2.94 IU/mL in cases. Conclusion. The severity of preeclampsia and eclampsia was not associated with thyroid function tests. The only significant value was low T3 level among pregnancy, induced hypertensive patients.

Mild maternal thyroid dysfunction at delivery of infants born ≤34 weeks and neurodevelopmental outcome at 5.5 years

CONTEXT

Mild maternal thyroid dysfunction during early pregnancy is associated with poor neurodevelopment in affected offspring. Most studies are population based or are smaller populations of term/late preterm infants. No studies were found that focused on more preterm infants.

OBJECTIVE

Our objective was to describe the relationship between mild maternal thyroid dysfunction at delivery of infants born ≤34 wk and neurodevelopment at 5.5 yr.

DESIGN

The study design was follow-up of women and children recruited in Scotland between 1998 and 2001.

MAIN OUTCOME

We evaluated delivery levels of maternal TSH, free T(4) (FT(4)), and T(4) and the association with McCarthy Scale scores adjusted for 26 confounders of neurodevelopment.

RESULTS

Maternal serum levels and McCarthy scores were available for 143 women and 166 children. After adjustment for confounders, there were significant 3.2, 2.1, and 1.8 point decrements, respectively, in general cognitive index, verbal subscale, and the perceptual performance subscale for each milliunit per liter increment in maternal TSH. Maternal FT(4) levels were variably associated with neurodevelopment. After adjustment, significant associations were found for the general cognitive index, motor scale, and quantitative subscale; each picomole per liter decrease in FT(4) was associated with an increase of 1.5, 1.7, and 0.9 points, respectively. Maternal T(4) levels showed little relationship with neurodevelopment. None of the women in this analysis had overt hypothyroidism, but mild hypothyroidism was evident in 27%; thyroglobulin antibody (TgAb) was ≥ 40 U/ml in 28% of the women.

CONCLUSIONS

Higher maternal levels of TSH at delivery of infants born preterm were associated with significantly lower scores on the general cognitive index at 5.5 yr.

Mid-gestational maternal free thyroxine concentration and offspring neurocognitive development at age two years

CONTEXT

Lower neurocognitive development scores at age 2 yr have been reported in association with euthyroid hypothyroxinemia during early pregnancy.

OBJECTIVE

The objective of this study was to further explore this association with euthyroid hypothyroxinemia during early pregnancy.

DESIGN

This was an observational, nested case-control study.

SETTING

The study was conducted at physician offices and prenatal clinics throughout Maine.

STUDY SUBJECTS

Between May 2004 and March 2006, TSH was measured in 5734 women in conjunction with second-trimester Down syndrome screening. After completion of pregnancy, free T(4) was measured in stored second-trimester sera from euthyroid women (TSH 0.1-3.5 mIU/ml; n = 5560). Women with free T(4) at the third centile or less (n = 99) were matched with women whose free T(4) was at the 10th to the 90th centile (n = 99).

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURE

Bayley Scales of Infant Development (BSID III) were administered to the 198 offspring at age 2 yr. Scores for cognitive, language, and motor development were compared between matched pairs of offspring from the two groups before and after correcting for relevant variables.

RESULTS

Unadjusted BSID-III scores (cognitive, language, and motor) were lower by about 3% at age 2 yr among offspring of 98 hypothyroxinemic women (cases), reaching borderline significance for cognitive and motor scores. After adjustment for gestational age, the child's age at testing, maternal weight, and education, all differences diminished and became nonsignificant. Scores less than 85 were more frequent among case children but did not reach statistical significance (P = 0.14).

CONCLUSIONS

Isolated hypothyroxinemia during the second trimester is not associated with significantly lower BSID-III scores at age 2 yr, compared with scores for offspring of matched euthyroxinemic women.

Free thyroxine level in the high normal reference range prescribed for nonpregnant women may reduce the preterm delivery rate in multiparous

Preterm birth is the most common reason for perinatal morbidity and mortality in the western world. It has been shown that in euthyreotic pregnant women with thyroid autoimmune antibodies, L-Thyroxine replacement reduces preterm delivery rate in singleton pregnancies. We investigated in a nonrandomized retrospective observational study whether L-Thyroxine replacement, maintaining maternal free thyroxine serum level in the high normal reference range prescribed for nonpregnant women also influences the rate of preterm delivery in women without thyroid autoimmune antibodies. As control group for preterm delivery rate, data from perinatal statistics of the State of Baden-Württemberg from 2006 were used. The preterm delivery rate in the study group was significantly reduced. The subgroup analysis shows no difference in primiparous but a decline in multiparous by approximately 61% with L-Thyroxine replacement. Maintaining free thyroxine serum level in the high normal reference range prescribed for nonpregnant women may reduce the preterm delivery rate.

Subclinical hypothyroidism and related biochemical entities in pregnancy: implications and management

Subclinical hypothyroidism (SCH), thyroid autoimmunity and isolated maternal hypothyroxinaemia are diagnoses made on laboratory findings. The two former conditions are commonly identified in the general population, while the term isolated maternal hypothyroxinaemia was developed to highlight potential neurodevelopmental risks in progeny. Each entity has been associated with either obstetric, perinatal and/or child developmental harm in observational studies, although few interventional trials have been performed to guide diagnostic and therapeutic approaches. Once diagnosed, treatment of SCH is recommended by endocrine groups to limit potential risk, given that harm from appropriate therapy is unlikely. Screening for thyroid disorders in pregnancy has traditionally been controversial. Definitive trials are expected to report over coming years and updated consensus guidelines will hopefully resolve this issue.

Levels of neonatal thyroid hormone in preterm infants and neurodevelopmental outcome at 5 1/2 years: millennium cohort study

CONTEXT

Transient hypothyroxinemia is the commonest thyroid dysfunction of premature infants, and recent studies have found adverse associations with neurodevelopment. The validity of these associations is unclear because the studies adjusted for a differing range of factors likely to influence neurodevelopment.

OBJECTIVE

The aim was to describe the association of transient hypothyroxinemia with neurodevelopment at 5.5 yr corrected age.

DESIGN

We conducted a follow-up study of a cohort of infants born in Scotland from 1999 to 2001 ≤34 wk gestation.

MAIN OUTCOME MEASURES

We measured scores on the McCarthy scale adjusted for 26 influences of neurodevelopment including parental intellect, home environment, breast or formula fed, growth retardation, and use of postnatal drugs.

RESULTS

A total of 442 infants ≤34 wk gestation who had serum T(4) measurements on postnatal d 7, 14, or 28 and 100 term infants who had serum T(4) measured in cord blood were followed up at 5.5 yr. Infants with hypothyroxinemia (T(4) level ≤ 10th percentile on d 7, 14, or 28 corrected for gestational age) scored significantly lower than euthyroid infants (T(4) level greater than the 10th percentile and less than the 90th percentile on all days) on all McCarthy scales, except the quantitative. After adjustment for confounders of neurodevelopment, hypothyroxinemic infants scored significantly lower than euthyroid infants on the general cognitive and verbal scales.

CONCLUSIONS

Our findings do not support the view that the hypothyroxinemic state, in the context of this analysis, is harmless in preterm infants. Many factors contribute both to the etiology of hypothyroxinemia and neurodevelopment; strategies for correction of hypothyroxinemia should acknowledge its complex etiology and not rely solely on one approach.

[Thyroid and pregnancy]

Pregnancy is associated with an increased requirement of hormone secretion by the thyroid, within the first weeks after conception. To this greater demand to occurs, pregnancy induces a series of physiological changes that affect thyroid function and, consequently, the tests of glandular function. For normal pregnant women living in areas with a sufficient supply of iodine, this challenge regarding the adjustment of thyroid hormone releases to this new state of equilibrium and its maintenance until the end of pregnancy it meets no difficulties. However, among women with impaired thyroid function due to some thyroid disease or among women residing in areas with an insufficient iodine supply, this does not occur. The management of thyroid dysfunction during gestation requires special considerations, since both hypothyroidism and hyperthyroidism can lead to maternal and fetal complications. In addition, thyroid nodules are detected at reasonable frequency among pregnant women, a fact that requires a differential diagnosis between benign and malignant growths during the pregnancy itself.

Autoimmune Thyroid Disease and Pregnancy: Relevance for the Child

As a group, the autoimmune thyroid diseases, including Graves' disease, Hashimoto's thyroiditis, and primary myxedema, are among the most common endocrine disorders encountered during pregnancy. Therefore, a substantial number of offspring will grow and develop in utero under conditions of maternal autoimmune thyroid disease and may be exposed to abnormal maternal thyroid function, maternal thyroid antibodies, and/or numerous therapeutic agents used to manage maternal thyroid dysfunction. This article reviews the effects that these various aspects of maternal autoimmune thyroid disorders can have on pregnancy outcome, as well as on the physical growth, neuropsychological development, and thyroid status of the developing fetus and neonate.

Sensory neuron sodium current requires nongenomic actions of thyroid hormone during development

Development of the embryonic nervous system requires thyroid hormone. However, the underlying mechanisms and targets of thyroid hormone action are not well defined. To identify embryonic roles for thyroid hormone we tested for effects on a key neuronal trait, voltage-gated sodium current (I(Na)), in the zebrafish model system. We recorded from Rohon-Beard sensory neurons (RBs) using whole cell voltage-clamp methods. Here, we provide in vivo evidence for thyroid hormone regulation of I(Na). Chronic thyroid hormone application increased RB peak I(Na) density 1.4-fold. However, I(Na) density showed a similar increase within 5 min of an acute hormone application, a time course not expected for a genomic mechanism. Tetraiodothyroacetic acid (tetrac), a thyroid hormone blocker, blocked both chronic and acute effects. Further, the thyroid hormone precursor thyroxine (T4) affected I(Na), yet the traditionally active form triiodothyronine did not. Consequently, we tested for a nonconventional T4 receptor. LM609, a selective antagonist of integrin alphaVbeta3, occluded the rapid effect of T4, implicating a specific integrin dimer as a T4 receptor. Chronic application of either tetrac or LM609 significantly reduced sodium conductance, demonstrating an in vivo requirement for T4-integrin regulation of I(Na). Further, removing endogenous T4 levels via yolkectomy reduced sodium conductance, an effect that was partially rescued by T4 supplementation following surgery. Because RBs mediate the embryonic touch response, we tested for behavioral effects. Tetrac and LM609 significantly reduced the percentage of touch trials eliciting a normal touch response. T4's rapid effect on RB I(Na) highlights the importance of embryonic T4 availability and nongenomic T4 signaling.

Maternal thyroid hypofunction and pregnancy outcome

OBJECTIVE

To estimate whether maternal thyroid hypofunction is associated with complications.

METHODS

A total of 10,990 patients had first- and second-trimester serum assayed for thyroid-stimulating hormone (TSH), free thyroxine (freeT4), and antithyroglobulin and antithyroid peroxidase antibodies. Thyroid hypofunction was defined as 1) subclinical hypothyroidism: TSH levels above the 97.5th percentile and free T4 between the 2.5th and 97.5th percentiles or 2) hypothyroxinemia: TSH between the 2.5th and 97.5th percentiles and free T4 below the 2.5th percentile. Adverse outcomes were evaluated. Patients with thyroid hypofunction were compared with euthyroid patients (TSH and free T4 between the 2.5th and 97.5th percentiles). Patients with and without antibodies were compared. Multivariable logistic regression analysis adjusted for confounders was used.

RESULTS

Subclinical hypothyroidism was documented in 2.2% (240 of 10,990) in the first and 2.2% (243 of 10,990) in the second trimester. Hypothyroxinemia was documented in 2.1% (232 of 10,990) in the first and 2.3% (247 of 10,990) in the second trimester. Subclinical hypothyroidism was not associated with adverse outcomes. In the first trimester, hypothyroxinemia was associated with preterm labor (adjusted odds ratio [aOR] 1.62; 95% confidence interval [CI] 1.00-2.62) and macrosomia (aOR 1.97; 95% CI 1.37-2.83). In the second trimester, it was associated with gestational diabetes (aOR 1.7; 95% CI 1.02-2.84). Fifteen percent (1,585 of 10,990) in the first and 14% (1,491 of 10,990) in the second trimester had antithyroid antibodies. When both antibodies were positive in either trimester, there was an increased risk for preterm premature rupture of membranes (P=.002 and P<.001, respectively).

CONCLUSION

Maternal thyroid hypofunction is not associated with a consistent pattern of adverse outcomes.

LEVEL OF EVIDENCE

II.

Loss of integrity of thyroid morphology and function in children born to mothers with inadequately treated Graves' disease

CONTEXT

Central congenital hypothyroidism (CH-C) in neonates born to mothers with inadequately treated Graves' disease usually needs T(4) supplementation. The thyroid and its regulatory system have not yet been extensively studied after T(4) withdrawal, until we observed disintegrated thyroid glands in some patients.

OBJECTIVE

The aim was to study the occurrence and pathogenesis of disintegrated thyroid glands in CH-C patients. DESIGN, SETTING, PATIENTS, PARTICIPANTS: Thyroid function was measured and thyroid ultrasound imaging was performed in 13 children with CH-C due to inadequately treated maternal Graves' disease after T(4)-supplementation withdrawal (group Aa). In addition, thyroid ultrasound imaging was performed in six children with CH-C born to inadequately treated mothers with Graves' disease, in whom T(4) supplementation was not withdrawn yet (group Ab) or never initiated (group Ac), in six euthyroid children born to adequately treated mothers with Graves' disease (group B), and in 10 T(4)-supplemented children with CH-C as part of multiple pituitary hormone deficiency (group C).

MAIN OUTCOME MEASURES

Thyroid function and aspect (volume, echogenicity, echotexture) were measured.

RESULTS

In group A, five children had developed thyroidal hypothyroidism characterized by persistently elevated TSH concentrations and exaggerated TSH responses after TRH stimulation. In the majority of patients in groups A and C, thyroid echogenicity and volume were decreased, and echotexture was inhomogeneous. Thyroid ultrasound imaging was normal in group B children.

CONCLUSIONS

Inadequately treated maternal Graves' disease not only may lead to CH-C but also carries an, until now, unrecognized risk of thyroid disintegration in the offspring as well. We speculate that insufficient TSH secretion due to excessive maternal-fetal thyroid hormone transfer inhibits physiological growth and development of the child's thyroid.

General background on the hypothalamic-pituitary-thyroid (HPT) axis

This article reviews the thyroid system, mainly from a mammalian standpoint. However, the thyroid system is highly conserved among vertebrate species, so the general information on thyroid hormone production and feedback through the hypothalamic-pituitary-thyroid (HPT) axis should be considered for all vertebrates, while species-specific differences are highlighted in the individual articles. This background article begins by outlining the HPT axis with its components and functions. For example, it describes the thyroid gland, its structure and development, how thyroid hormones are synthesized and regulated, the role of iodine in thyroid hormone synthesis, and finally how the thyroid hormones are released from the thyroid gland. It then progresses to detail areas within the thyroid system where disruption could occur or is already known to occur. It describes how thyroid hormone is transported in the serum and into the tissues on a cellular level, and how thyroid hormone is metabolized. There is an in-depth description of the alpha and beta thyroid hormone receptors and their functions, including how they are regulated, and what has been learned from the receptor knockout mouse models. The nongenomic actions of thyroid hormone are also described, such as in glucose uptake, mitochondrial effects, and its role in actin polymerization and vesicular recycling. The article discusses the concept of compensation within the HPT axis and how this fits into the paradigms that exist in thyroid toxicology/endocrinology. There is a section on thyroid hormone and its role in mammalian development: specifically, how it affects brain development when there is disruption to the maternal, the fetal, the newborn (congenital), or the infant thyroid system. Thyroid function during pregnancy is critical to normal development of the fetus, and several spontaneous mutant mouse lines are described that provide research tools to understand the mechanisms of thyroid hormone during mammalian brain development. Overall this article provides a basic understanding of the thyroid system and its components. The complexity of the thyroid system is clearly demonstrated, as are new areas of research on thyroid hormone physiology and thyroid hormone action developing within the field of thyroid endocrinology. This review provides the background necessary to review the current assays and endpoints described in the following articles for rodents, fishes, amphibians, and birds.

Subclinical hypothyroidism

PURPOSE OF REVIEW

Mild or subclinical hypothyroidism is characterized by normal serum free thyroxine concentrations with elevated serum thyroid-stimulating hormone concentrations. Subclinical hypothyroidism is relatively prevalent in the general population, especially among women and the elderly. The main cause of subclinical hypothyroidism is autoimmune chronic thyroiditis. The present report reviews the most important and recent studies on subclinical hypothyroidism, and discusses the most controversial aspects of this topic.

RECENT FINDINGS

Several studies have demonstrated that subclinical hypothyroidism may affect both diastolic and systolic cardiac function. It may also worsen many risk factors for cardiovascular disease, including hypertension, abnormal endothelial function, and elevated low-density lipoprotein cholesterol concentrations. Furthermore, a growing body of evidence suggests that subclinical hypothyroidism may cause symptoms or progress to symptomatic overt hypothyroidism.

SUMMARY

Prompt treatment of subclinical hypothyroidism in pregnant women is mandatory to decrease risks for pregnancy complications and impaired cognitive development in offspring. Children with subclinical hypothyroidism should be treated to prevent growth retardation. Whether nonpregnant adult patients with subclinical hypothyroidism should be treated, and at what thyroid-stimulating hormone values, is debatable.

Risk factors of primary thyroid dysfunction in early infants born to mothers with autoimmune thyroid disease

AIM

To assess whether the state of maternal thyroid function and the pattern of thyroid alterations during gestation would affect the infants' thyroid function and to evaluate the risk factors affecting early infants' thyroid function by means of multiple logistic regression.

METHODS

In a cross-sectional study, 78 neonates born to mothers with Graves disease or Hashimoto thyroiditis were examined and followed clinically and biochemically. Neonates born to healthy mothers during the same period were set as controls. Tests of thyroid function, antithyroid peroxidase antibody (TPOAb), antithyroglobulin antibody (TGAb), anti-TSH receptor antibody (TRAb) and antithyroid-stimulating antibody (TSAb) were performed both in early infants and their mothers. All possible maternal and/or infantile risk factors for thyroid dysfunction during early infancy were analysed by means of multiple-factor logistical regression.

RESULTS

The overall prevalence of underlying subtle thyroid abnormalities in these 78 infants was 52.6%, which was significantly higher than that witnessed among infants from healthy mothers (5.4 per thousand, p<0.01). By using multiple logistic regression analysis, the state of maternal thyroid function in gestation, the type of autoimmune thyroid disease during pregnancy and the level of TRAb in the newborn were significantly correlated with the early infants' thyroid dysfunction.

CONCLUSION

Maternal autoimmune thyroid disease during pregnancy will affect infant thyroid function. Therefore, appropriate management of maternal autoimmune thyroid disease throughout pregnancy is essential in the prevention of undesirable neonatal outcomes.

Maternal hypothyroxinaemia during early pregnancy and subsequent child development: a 3-year follow-up study

OBJECTIVE

To evaluate the impact of maternal hypothyroxinaemia during early gestation (fT4 below the lowest tenth percentile and TSH within the reference range: 0.15-2.0 mIU/l) on infant development, together with any subsequent changes in fT4 during gestation.

DESIGN

A prospective 3-year follow-up study of pregnant women and their children up to the age of 2 years.

MEASUREMENTS

Child development was assessed by means of the Bayley Scales of Infant Development in children of women with hypothyroxinaemia (fT4 below the tenth percentile at 12 weeks' gestation) at 12 weeks' gestation (cases), and in children of women with fT4 between the 50th and 90th percentiles at 12 weeks' gestation, matched for parity and gravidity (controls). Maternal thyroid function (fT4 and TSH) was assessed at 12, 24 and 32 weeks' gestation. The mental and motor function of 63 cases and 62 controls was compared at the age of 1 year, and of 57 cases and 58 controls at the age of 2 years.

RESULTS

Children of women with hypothyroxinaemia at 12 weeks' gestation had delayed mental and motor function compared to controls: 10 index points on the mental scale (95% CI: 4.5-15 points, P = 0.003) and eight on the motor scale at the age of 1 year (95% CI: 2.3-12.8 points, P = 0.02), as well as eight index points on the mental (95% CI: 4-12 points, P = 0.02), and 10 on the motor scale (95%CI: 6-16 points, P = 0.005) at the age of 2 years. Children of hypothyroxinaemic women in whom the fT4 concentration was increased at 24 and 32 weeks' gestation had similar scores to controls, while in the controls, the developmental scores were not influenced by further declines in maternal fT4 at 24 and 32 weeks' gestation.

CONCLUSIONS

Maternal hypothyroxinaemia during early gestation is an independent determinant of a delay in infant neurodevelopment. However, when fT4 concentrations increase during pregnancy in women who are hypothyroxinaemic during early gestation, infant development appears not to be adversely affected.

Effects of hypergravity exposure on the developing central nervous system: possible involvement of thyroid hormone

The present study examined the effects of hypergravity exposure on the developing brain and specifically explored the possibility that these effects are mediated by altered thyroid status. Thirty-four timed-pregnant Sprague-Dawley rats were exposed to continuous centrifugation at 1.5 G (HG) from gestational Day 11 until one of three key developmental points: postnatal Day (P) 6, P15, or P21 (10 pups/dam: 5 males/5 females). During the 32-day centrifugation, stationary controls (SC, n = 25 dams) were housed in the same room as HG animals. Neonatal body, forebrain, and cerebellum mass and neonatal and maternal thyroid status were assessed at each time point. The body mass of centrifuged neonates was comparatively lower at each time point. The mass of the forebrain and the mass of the cerebellum were maximally reduced in hypergravity-exposed neonates at P6 by 15.9% and 25.6%, respectively. Analysis of neonatal plasma suggested a transient hypothyroid status, as indicated by increased thyroid stimulating hormone (TSH) level (38.6%) at P6, while maternal plasma TSH levels were maximally elevated at P15 (38.9%). Neither neonatal nor maternal plasma TH levels were altered, suggesting a moderate hypothyroid condition. Thus, continuous exposure of the developing rats to hypergravity during the embryonic and neonatal periods has a highly significant effect on the developing forebrain and cerebellum and neonatal thyroid status (P < 0.05, Bonferroni corrected). These data are consistent with the hypothesized role of the thyroid hormone in mediating the effect of hypergravity in the developing central nervous system and begin to define the role of TH in the overall response of the developing organism to altered gravity.