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

Maternal hypothyroxinaemia in early pregnancy and school performance in 5-year-old offspring

OBJECTIVE

Overt hypothyroidism in pregnant women is associated with a lower intelligence quotient in their children. More recently, subtle decreases in maternal thyroid function have also been associated with neurodevelopmental impairment in offspring. We tested the effect of hypothyroxinaemia during early pregnancy on school performance.

DESIGN

This was a longitudinal study that included the data of 1196 mother-child pairs from the Amsterdam Born Children and Their Development study.

METHODS

Maternal serum free thyroxine (T4) and TSH were obtained at a median gestational age of 12.9 (interquartile range: 11.9-14.3) weeks. School performance was assessed at age 5 years and based on scores obtained in arithmetic and language tests from the national monitoring and evaluation system. Poor school performance was defined as a test result <25th percentile and subnormal school performance as a result <50th percentile of the norm population. To estimate the impact of possible non-response bias, we conducted inverse-probability weighted analyses.

RESULTS

Maternal hypothyroxinaemia (i.e., a maternal free T4 in the lowest 10% of distribution) was associated with a 1.61 (95% CI: 1.05-2.47) -fold increased odds of subnormal arithmetic performance after adjustment for confounders (P=0.03). However, the odds ratio dropped to 1.48 (95% CI: 0.94-2.32) after inverse-probability weighting (P=0.09). No such relations were found with TSH.

CONCLUSIONS

Maternal hypothyroxinaemia at the end of the first trimester was associated with reduced performance in an arithmetic test, but not in a language test, in 5-year-old offspring. However, our results should be interpreted carefully because of possible non-response bias.

Different Degrees of Iodine Deficiency Inhibit Differentiation of Cerebellar Granular Cells in Rat Offspring, via BMP-Smad1/5/8 Signaling

Iodine deficiency (ID) during development results in dysfunction of the central nervous system (CNS) and affects psychomotor and motor function. It is worth noting that maternal mild and marginal ID tends to be the most common reason of preventable neurodevelopmental impairment, via a mechanism that has not been elucidated. Therefore, our aim was to study the effects of developmental mild and marginal ID on the differentiation of cerebellar granule cells (GCs) and investigate the activation of BMP-Smad1/5/8 signaling, which is crucial for the development and differentiation of cerebellum. Three developmental rat models were created by feeding dam rats with a diet deficient in iodine and deionized water supplemented with potassium iodide. Our results showed that different degrees of ID inhibited and delayed the differentiation of cerebellar GCs on postnatal day (PN) 7, PN14, and PN21. Moreover, mild and severe ID reduced the expression of BMP2 and p-Smad1/5/8, and increased the levels of Id2 on PN7, PN14, and PN21. However, marginal ID rarely altered expression of these proteins in the offspring. Our study supports the hypothesis that mild and severe ID during development inhibits the differentiation of cerebellar GCs, which may be ascribed to the down-regulation of BMP-Smad1/5/8 signaling and the overexpression of Id2. Furthermore, it was speculated that maternal marginal ID rarely affected the differentiation of cerebellar GCs in the offspring.

The importance of iodine in public health

Iodine (I) deficiency has been known for more than a century and is known to cause cretinism at the extreme end of the spectrum but also, importantly, impaired development and neurocognition in areas of mild deficiency. The WHO has indicated that median urinary iodine of 100-199 μg/l in a population is regarded as indicative of an adequate iodine intake. The understanding of the spectrum of iodine deficiency disorders led to the formation of The International Council for the Control of Iodine Deficiency Disorders which has promulgated the use of household iodized salt and the use of such salt in food processing and manufacture. Iodine deficiency is particularly important in pregnancy as the fetus relies on maternal thyroxine (T4) exclusively during the first 14 weeks and also throughout gestation. As this hormone is critical to brain and nervous system maturation, low maternal T4 results in low child intelligence quotient. The recommendation for I intake in pregnancy is 250 μg/day to prevent fetal and child brain function impairment. During the past 25 years, the number of countries with I deficiency has reduced to 32; these still include many European developed countries. Sustainability of adequate iodine status must be achieved by continuous monitoring and where this has not been performed I deficiency has often recurred. More randomized controlled trials of iodine supplementation in pregnancy are required in mild iodine-deficient areas to inform public health strategy and subsequent government action on suitable provision of iodine to the population at risk.

Iron deficiency, an independent risk factor for isolated hypothyroxinemia in pregnant and nonpregnant women of childbearing age in China

CONTEXT

Isolated hypothyroxinemia during early pregnancy may irreversibly damage the neurodevelopment of offspring. However, the causes are not well clarified.

OBJECTIVE

To explore the association of iron deficiency (ID) with hypothyroid function of women in early pregnancy and nonpregnant women.

DESIGN

A total of 7953 pregnant women of ≤ 12 weeks gestation and 2000 childbearing-aged women were recruited. A subpopulation including 3340 pregnant women and 1052 nonpregnant women with sufficient iodine intake and negative thyroid peroxidase antibody were studied. Mild and severe cases of hypothyroxinemia were defined as free T4 levels below the 10th percentile and the 5th percentile, respectively, with normal TSH. Total body iron, serum ferritin, and serum transferrin receptor were used as indicators for iron nutrition.

RESULTS

Serum free T4 levels were significantly lower in both pregnant and nonpregnant women with ID compared with the corresponding groups without ID (both P < .05). The prevalence of mild and severe hypothyroxinemia was markedly higher in women with ID than those without, in both pregnant and nonpregnant women (all P < .01). Logistic regression indicated that ID was an independent risk factor for both mild and severe hypothyroxinemia in pregnancy (odds ratio [OR] = 2.440, 95% confidence interval [CI]: 1.324-4.496, P = .004; and OR = 3.278, 95% CI: 1.443-7.446, P = .005, respectively) and nonpregnancy (OR = 2.662, 95% CI: 1.330-5.329, P = .006; and OR = 3.254, 95% CI: 1.375-7.700, P = .007, respectively).

CONCLUSIONS

An association between ID and isolated hypothyroxinemia was found in both pregnant and nonpregnant childbearing-aged women, independent of the effects of iodine and thyroid autoimmunity. We speculate that ID may be a pathogenic factor for hypothyroxinemia, even in pregnant women during the first trimester.

Maternal Hypothyroxinemia-Induced Neurodevelopmental Impairments in the Progeny

Maternal hypothyroxinemia can induce neurodevelopmental impairments in the developing fetus. We here review recent studies on the epidemiology and molecular mechanisms associated with this important public health issue. In 2011, the American Thyroid Association defined maternal hypothyroxinemia as low serum free thyroxine (FT4) levels (<5th or <10th percentile) existing in conjunction with normal serum free triiodothyronine (FT3) or thyroid stimulating hormone (TSH) levels during pregnancy. Compared to clinical or subclinical hypothyroidism, hypothyroxinemia is more commonly found in pregnant women. Hypothyroxinemia usually ensues in response to several factors, such as mild iodine deficiency, environmental endocrine disrupters, or certain thyroid diseases. Unequivocal evidence demonstrates that maternal hypothyroxinemia leads to negative effects on fetal brain development, increasing the risks for cognitive deficits and poor psychomotor development in resulting progeny. In support of this, rodent models provide direct evidence of neurodevelopmental damage induced by maternal hypothyroxinemia, including dendritic and axonal growth limitation, neural abnormal location, and synaptic function alteration. The neurodevelopmental impairments induced by hypothyroxinemia suggest an independent role of T4. Increasing evidence indicates that adequate thyroxine is required for the mothers in order to protect against the abnormal brain development in their progeny.

Developmental hypothyroxinaemia and hypothyroidism limit dendritic growth of cerebellar Purkinje cells in rat offspring: involvement of microtubule-associated protein 2 (MAP2) and stathmin

AIMS

Iodine is essential for the synthesis of thyroid hormone. Iodine deficiency (ID)-induced hypothyroxinaemia and hypothyroidism during developmental period contribute to impairments of function in the brain, such as psychomotor and motor alterations. However, the mechanisms are still unclear. Therefore, the present research is to study the effects of developmental hypothyroxinaemia caused by mild ID and developmental hypothyroidism caused by severe ID or methimazole (MMZ) on dendritic growth in filial cerebellar Purkinje cells (PCs) and the underlying mechanisms.

METHODS

A maternal hypothyroxinaemia model was established in Wistar rats using a mild ID diet, and two maternal hypothyroidism models were developed with either severe ID diet or MMZ water. We examined the total dendritic length using immunofluorescence, and Western blot analysis was conducted to investigate the activity of microtubule-associated protein 2 (MAP2), stathmin and calcium/calmodulin-dependent protein kinase II (CaMKII).

RESULTS

Hypothyroxinaemia and hypothyroidism reduced the total dendritic length of cerebellar PCs, decreased MAP2 and its phosphorylation, increased stathmin but reduced its phosphorylation and down-regulated the activity of CaMKII and its phosphorylation in cerebellar PCs on postnatal day (PN) 7, PN14 and PN21.

CONCLUSION

Developmental hypothyroxinaemia induced by mild ID and hypothyroidism induced by severe ID or MMZ limit PCs dendritic growth, which may involve in the disturbance of MAP2 and stathmin in a CaMKII-dependent manner. It suggests a potential mechanism of motor coordination impairments caused by developmental hypothyroxinaemia and hypothyroidism.

Thyroid diseases during pregnancy: a number of important issues

The most common thyroid diseases during pregnancy are hyper- and hypothyroidism and their variants including isolated hypothyroxinemia (hypo-T4), autoimmune thyroid disease (AITD) and different types of goiter. AITD represents the main cause of hypothyroidism during pregnancy ranging in prevalence between 5 and 20% with an average of 7.8%. The incidence of isolated hypo-T4 is about 150 times higher compared to congenital hypothyroidism. Prevalence of Graves' disease (GD) ranges between 0.1% and 1% and the Transient Gestational Hyperthyroidism Syndrome between 1 and 3%. Thyroid stimulating hormone (TSH) is a sensitive marker of thyroid dysfunction during pregnancy. Normal values have been modified recently with a downward shift. Thus, the upper normal range is now considered to be 2.5 mUI/mL in the first trimester and 3.0 mUI/mL for the remainder of pregnancy. Most studies have shown that children born to women with hypothyroidism during gestation had significantly lower scores in neuropsychological tests related to intelligence, attention, language, reading ability, school performance and visual motor performance. However, some studies have not confirmed these findings. On the other hand, multiple retrospective studies have shown that the risks of maternal and fetal/neonatal complications are directly related to the duration and inadequate control of maternal thyrotoxicosis. The latter is associated with a risk of spontaneous abortion, congestive heart failure, thyrotoxic storm, preeclampsia, preterm delivery, low birth weight and stillbirth. Despite the lack of consensus among professional organizations, recent studies, which are based on sophisticated analyses, support universal screening in all pregnant women in the first trimester for thyroid diseases.

Normal intellectual development in children born from women with hypothyroxinemia during their pregnancy

Proper maternal thyroid function is known to be essential for neural differentiation and migration in the fetus during the first half of pregnancy. The objectives of this study were to assess the relationship between thyroxin levels, in pregnant women with no thyroid disease and the intellectual development of their offspring in a non-iodine-deficient area, and to know specifically whether or not isolated hypothyroxinemia during pregnancy was associated with a lower intelligence in the offspring. Previously we had publicated values TSH, FT4, free T3 (FT3), anti-thyroid peroxidase antibodies (TPO Abs) and urinary iodine concentration (UIC) in 1322 pregnant women in our hospital area. Now we presented results of intelligence quotient in children born from these pregnancies. We assessed 455 children at one year of age using Brunet-Lezine scale. Of these, 289 children were evaluated again at 6-8 years of age using the WISC-IV. From the total group of children recruited, we established as control subgroup, children born of rigorously normal pregnancies (women with UIC > 150 μg/L, FT4>10th percentile and TPO-Ab negative in both trimesters). The remaining children were divided into two subgroups: those born to mothers with FT4 below the 10th percentile and the rest. No correlation was found between FT4 maternal levels, in either of trimesters studied, and the intellectual scores of offspring. No differences were found in intellectual scores comparing children born to mothers with hypothyroxinemia and those whose mothers were euthyroxinemic in both trimesters, or with the control subgroup. As conclusions we did not find any association between the levels of maternal FT4 during pregnancy and the subsequent intellectual development the offspring from these pregnancies. We attribute this result to the fact that all the pregnant women included had normal thyroid function.

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.

Initiation of movement and energy expenditure in children with developmental delay: a case-control study

BACKGROUND

Lower levels of physical activity in children with developmental delay (DD) usually are attributed to higher energy costs. However, there is no evidence that children with DD spend more energy on daily physical activities, such as walking.

OBJECTIVE

The aim of this study was to compare energy costs during walking and movement initiation times in children with DD and children with typical development (TD) and matched for age.

DESIGN

This was a case-control study.

METHODS

Children who were 3 and 5 years old and had DD (n=12) or TD (n=12) participated in the study. Measurements included ranges of motion in the lower extremities, physiological costs of walking, and movement initiation times. A task designed to evaluate the initiation of movement (the "go play with the toy" task) was used to examine the reaction times for children's goal-directed walking.

RESULTS

The physiological costs of walking were similar in the 2 groups; however, children with DD walked at a lower speed than children with TD. Importantly, children with DD took more time to initiate goal-directed walking.

LIMITATIONS

The nature of the study design limited causal inference from the results.

CONCLUSIONS

Children who were 3 to 5 years old and had DD had delays in goal-directed movement that may not have been attributable to motor impairments. The findings suggest that therapists should evaluate the movement initiation ability of 3- to 5-year-old children with DD as part of the design of an overall intervention plan.

Downstream effects of maternal hypothyroxinemia in early pregnancy: nonverbal IQ and brain morphology in school-age children

CONTEXT

Although maternal hypothyroxinemia is suggested to be related to various adverse consequences in a child's neurodevelopment, the underlying neurobiology is largely unknown.

OBJECTIVE

The objective of the study was to examine the relationship between maternal hypothyroxinemia in early pregnancy and children's nonverbal intelligence quotient (IQ). Furthermore, we explored whether global brain volumes, cortical thickness, and brain surface area differed between children exposed prenatally to hypothyroxinemia and healthy controls.

DESIGN AND SETTING

The study included a large population-based prospective birth cohort in The Netherlands.

PARTICIPANTS

A total of 3727 mother-child pairs with data on prenatal thyroid function at less than 18 weeks of gestation and nonverbal IQ at 6 years participated in the study. In 652 children, brain imaging was performed at 8 years of age.

MAIN MEASURES

Maternal hypothyroxinemia was defined as free T4 in the lowest 5% of the sample, whereas TSH was in the normal range. At 6 years, children's IQ was assessed using a Dutch test battery. Global brain volumetric measures, cortical thickness, and surface area were assessed using high-resolution structural magnetic resonance imaging.

RESULTS

The children of mothers with hypothyroxinemia in early pregnancy scored 4.3 points IQ lower than the children of mothers with normal thyroid status (95% confidence interval -6.68, -1.81; P = .001). After adjustment for multiple testing, we did not find any differences in brain volumetric measures, cortical thickness, and surface area between children exposed prenatally to hypothyroxinemia and controls.

CONCLUSIONS

Our findings confirm a large adverse effect of maternal hypothyroxinemia on children's nonverbal IQ at school age. However, we found no evidence that maternal hypothyroxinemia is associated with differences in brain morphology in school-age children.

2014 European thyroid association guidelines for the management of subclinical hypothyroidism in pregnancy and in children

This guideline has been produced as the official statement of the European Thyroid Association guideline committee. Subclinical hypothyroidism (SCH) in pregnancy is defined as a thyroid-stimulating hormone (TSH) level above the pregnancy-related reference range with a normal serum thyroxine concentration. Isolated hypothyroxinaemia (defined as a thyroxine level below the 2.5th centile of the pregnancy-related reference range with a normal TSH level) is also recognized in pregnancy. In the majority of SCH the cause is autoimmune thyroiditis but may also be due to iodine deficiency. The cause of isolated hypothyroxinaemia is usually not apparent, but iodine deficiency may be a factor. SCH and isolated hypothyroxinaemia are both associated with adverse obstetric outcomes. Levothyroxine therapy may ameliorate some of these with SCH but not in isolated hypothyroxinaemia. SCH and isolated hypothyroxinaemia are both associated with neuro-intellectual impairment of the child, but there is no evidence that maternal levothyroxine therapy improves this outcome. Targeted antenatal screening for thyroid function will miss a substantial percentage of women with thyroid dysfunction. In children SCH (serum TSH concentration >5.5-10 mU/l) normalizes in >70% and persists in the majority of the remaining patients over the subsequent 5 years, but rarely worsens. There is a lack of studies examining the impact of SCH on the neuropsychological development of children under the age of 3 years. In older children, the evidence for an association between SCH and impaired neuropsychological development is inconsistent. Good quality studies examining the effect of treatment of SCH in children are lacking.

A 2013 survey of clinical practice patterns in the management of primary hypothyroidism

CONTEXT

In 2012, comprehensive clinical practice guidelines (CPGs) were published regarding the management of hypothyroidism.

OBJECTIVE

We sought to document current practices in the management of primary hypothyroidism and compare these results with recommendations made in the 2012 American Thyroid Association (ATA)/American Association of Clinical Endocrinologists (AACE) hypothyroidism CPGs. In addition, we sought to examine differences in management among international members of U.S.-based endocrine societies and to compare survey results with those obtained from a survey of ATA members performed 12 years earlier.

METHODS

Clinical members of The Endocrine Society (TES), the ATA, and the AACE were asked to take a web-based survey consisting of 30 questions dealing with testing, treatment, and modulating factors in the management of primary hypothyroidism.

RESULTS

In total, 880 respondents completed the survey, including 618 members of TES, 582 AACE members, and 208 ATA members. North American respondents accounted for 67.6%, Latin American 9.7%, European 9.2%, Asia and Oceania 8.1%, and Africa and Middle East 5.5%. Overt hypothyroidism would be treated using l-T4 alone by 99.2% of respondents; 0.8% would use combination l-T4 and liothyronine (l-T3) therapy. Generic l-T4 would be used by 49.3% and a brand name by 49.9%. The rate of replacement would be gradual (38.5%); an empiric dose, adjusted to achieve target (33.6%); or a calculated full replacement dose (27.8%). A target TSH of 1.0 to 1.9 mU/L was favored in the index case, but 3.0 to 3.9 mU/L was the most commonly selected TSH target for an octogenarian. Persistent hypothyroid symptoms despite achieving a target TSH would prompt testing for other causes by 84.3% of respondents, a referral to primary care by 11.3%, and a change to l-T4 plus l-T3 therapy by 3.6%. Evaluation of persistent symptoms would include measurement of T3 levels by 21.9% of respondents. Subclinical disease with a TSH 5.0 to 10.0 mU/L would be treated without further justification by 21.3% of respondents, or in the presence of positive thyroid peroxidase antibodies (62.3%), hypothyroid symptoms (60.9%), high low-density lipoprotein (52.9%), or goiter (46.6%). The TSH target for a newly pregnant patient was <2.5 mU/L for 96.1% of respondents, with 63.5% preferring a TSH target <1.5 mU/L. Thyroid hormone levels would be checked every 4 weeks during pregnancy by 67.7% and every 8 weeks by an additional 21.4%. A hypothyroid patient with TSH of 0.5 mU/L who becomes pregnant would receive an immediate l-T4 dose increase by only 36.9% of respondents.

CONCLUSION

The current survey of clinical endocrinologists catalogs current practice patterns in the management of hypothyroidism and demonstrates 1) a nearly exclusive preference for l-T4 alone as initial therapy, 2) the widespread use of age-specific TSH targets for replacement therapy, 3) a low threshold for treating mild thyroid failure, 4) meticulous attention to TSH targets in the pregnant and prepregnant woman, and 5) a highly variable approach to both the rate and means of restoring euthyroidism for overt disease. Both alignment and focal divergence from recent CPGs are demonstrated.

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

OBJECTIVES

Correct interpretation of thyroid status during pregnancy is vital to secure fetal development. Pregnancy-related changes in maternal thyroid status necessitate the use of gestational age-specific reference ranges. In this study, we investigated between-laboratory reproducibility of thyroid reference ranges in pregnant women.

DESIGN

Comparison of two longitudinal prospective cohort studies including 255 (cohort 1) and 101 (cohort 2) healthy antibody-negative Danish pregnant women attending prenatal care at Copenhagen University Hospital.

METHODS

Different immunoassays were used to measure thyroid hormone levels in the two cohorts. Thyroid hormone reference ranges were established for every 5 weeks of gestation. Differences between cohorts were explored through mixed-model repeated measures regression analyses. By applying reference ranges from one cohort to the other, the proportion of women who would be misclassified by doing so was investigated.

RESULTS

TSH increased and free thyroxine (FT4) decreased as pregnancy progressed. Results indicated highly significant differences between cohorts in free triiodothyronine (F=21.3, P<0.001) and FT4 (F=941, P<0.001). TSH levels were comparable (P=0.09). Up to 90.3% of the women had FT4 levels outside their laboratory's nonpregnant reference range, and up to 100% outside the other cohort's gestational-age-specific reference ranges. Z-score-based reference ranges markedly improved comparison between cohorts.

CONCLUSION

Even in the same region, the use of gestational-age-specific reference ranges from different laboratories led to misclassification. Up to 100% of maternal FT4 levels fell outside the other cohort's reference range despite similar TSH levels. In clinical practice, thyroid testing of pregnant women without adding method specificity to gestational age-dependent reference ranges will compromise patient safety.

The impact of gestational thyroid hormone concentrations on ADHD symptoms of the child

CONTEXT

Maternal hypothyroidism during pregnancy is associated with adverse neuropsychological development in the offspring.

OBJECTIVE

The objective of the study was to evaluate the effect of maternal thyroid dysfunction during pregnancy on a child's attention-deficit/hyperactivity disorder (ADHD) symptoms.

DESIGN, SETTINGS, AND PARTICIPANTS

The prospective, population-based Northern Finland Birth Cohort 1986 (9362 pregnancies; 9479 infants) included analysis of maternal TSH, free T4, and thyroid-peroxidase antibodies (TPO-Abs) from early pregnancy samples (5791 women). Teachers evaluated the children's ADHD symptoms at 8 years using the Rutter B2 scale (5131 mother-child pairs), in which a high score indicated probable psychiatric disorders and three questions focused directly on ADHD.

MAIN OUTCOME MEASURES

The odds ratios (ORs) and 95% confidence intervals (95% CIs) of child having ADHD symptoms and/or a high Rutter B2 score after exposure to increases in maternal TSH levels (after logarithmic transformation), low free T4 levels, and TPO-Ab positivity was tested with logistic regression, adjusting for maternal/family covariates. Data were stratified by the child's gender due to interaction.

RESULTS

Among girls the odds of inattention (OR 1.18, 95% CI 1.02-1.37), high Rutter B2 total score (OR 1.23, 95% CI 1.03-1.48), and combined ADHD symptoms (OR 1.39, 95% CI 1.07-1.80) significantly increased with every natural log increase in maternal TSH concentrations. Such findings were not evident in boys. No associations were seen between ADHD symptoms and low maternal free T4 levels or TPO-Ab positivity.

CONCLUSIONS

Increases in maternal TSH in early pregnancy showed weak but significant association with girls' ADHD symptoms.

Controversies in endocrinology: On the need for universal thyroid screening in pregnant women

There is a well-known controversy among scientific societies regarding the recommendation to screen for thyroid dysfunction (TD) during pregnancy. Although several studies have shown an association between maternal subclinical hypothyroidism and/or hypothyroxinemia with obstetric problems and/or neurocognitive impairment in the offspring, there is only limited evidence on the possible positive effects of thyroxine (T4) treatment in such cases. Despite the scarcity of this evidence, there is a widespread agreement among clinicians on the need for treatment of clinical hypothyroidism during pregnancy and the risks that could arise due to therapeutic abstention. As maternal TD is a quite prevalent condition, easily diagnosed and for which an effective and safe treatment is available, some scientific societies have proposed to assess thyroid function during the first trimester of pregnancy and ideally before week 10 of gestational age. Given the physiologic changes of thyroid function during pregnancy, hormone assessment should be performed using trimester-specific reference values ideally based on locally generated data as geographic variations have been detected. Screening of TD should be based on an initial determination of TSH performed early during the first trimester and only if abnormal should it be followed by either a free or total T4 measurement. Furthermore, adequate iodine supplementation during pregnancy is critical and if feasible it should be initiated before the woman attempts to conceive.

Five-year follow-up for women with subclinical hypothyroidism in pregnancy

CONTEXT

Increasing numbers of women are being treated with l-thyroxine in pregnancy for mild thyroid dysfunction because of its association with impaired neuropsychological development in their offspring and other adverse obstetric outcomes. However, there are limited data to indicate whether treatment should be continued outside of pregnancy.

OBJECTIVES

We aimed to determine whether subclinical hypothyroidism and maternal hypothyroxinemia resolve postdelivery.

DESIGN, SETTING, AND PARTICIPANTS

A total of 523 pregnant healthy women with no known thyroid disorders were recruited during routine antenatal care and provided blood samples at 28 weeks of pregnancy and at a mean of 4.9 years postpregnancy.

MAIN OUTCOME MEASURES

TSH, free T₄, free T₃, and thyroid peroxidase antibody levels were measured in serum taken in pregnancy and at follow-up.

RESULTS

Subclinical hypothyroidism in pregnancy (TSH >3 mIU/L) was present in 65 of 523 (12.4%) women. Of these, 49 (75.4%) women had normal thyroid function postpregnancy; 16 of 65 (24.6%) had persistent high TSH (TSH >4.5 mIU/L postpregnancy) with 3 women receiving l-thyroxine treatment. A total of 44 of 523 (8.4%) women had isolated maternal hypothyroxinemia in pregnancy (free T₄ <10th centile and TSH ≤3 mIU/L). Only 2 of 44 (4.5%) had TSH >4.5 mIU/L outside pregnancy. Of the women with subclinical hypothyroidism in pregnancy with antibody measurements available, those with thyroid peroxidase antibodies in pregnancy were more likely to have persistently elevated TSH or be receiving l-thyroxine replacement after pregnancy (6 of 7 [86%] vs 10 of 57 [18%], P < .001).

CONCLUSIONS

The majority of cases of subclinical hypothyroidism in pregnancy are transient, so treatment with l-thyroxine in these patients should be reviewed because it may not be warranted after pregnancy.

Hypothyroidism in pregnancy

Hypothyroidism is the most common pregnancy-related thyroid disorder, affecting 3-5% of all pregnant women. Subclinical hypothyroidism is more common than is overt hypothyroidism, and is usually defined as a serum thyroid-stimulating hormone (TSH) concentration greater than the pregnancy-specific reference range for each laboratory value, or by serum TSH concentrations greater than 2·5 mIU/L in the first trimester and greater than 3 mIU/L in the second and third trimesters. Some authors have defined subclinical hypothyroidism as a serum TSH between 5 and 10 mIU/L, and overt hypothyroidism as a serum TSH greater than 10 mIU/L, but this is not the commonly accepted definition. Once overt hypothyroidism is diagnosed, treatment with levothyroxine should be started to achieve serum TSH concentrations within the reference ranges for pregnancy as soon as possible. For patients with subclinical hypothyroidism, recommendations for therapy differ between various professional groups as a result of inconsistent data from both observational studies and clinical trials regarding the benefits for the mother or the child. Similarly, because benefits of therapy are still uncertain, universal screening of all pregnant women for subclinical hypothyroidism or thyroid autoimmunity is not recommended by most professional groups. During gestation, an increase in levothyroxine dose is required in more than 50% of women with previously diagnosed hypothyroidism, and can be managed by increasing the levothyroxine dose by 30% when pregnancy is confirmed.