The regulation of thyroid function in pregnancy: pathways of endocrine adaptation from physiology to pathology

Action of thyroid hormone in brain

Among the most critical actions of thyroid hormone in man and other mammals are those exerted on brain development. Severe hypothyroidism during the neonatal period leads to structural alterations, including hypomyelination and defects of cell migration and differentiation, with long-lasting, irreversible effects on behavior and performance. A complex regulatory mechanism operates in brain involving regulation of the concentration of the active hormone, T3, and the control of gene expression. Most brain T3 is formed locally from its precursor, T4, by the action of type II deiodinase which is expressed in glial cells, tanycytes, and astrocytes. Type III deiodinase (DIII) is also involved in the regulation of T3 concentrations, especially during the embryonic and early post-natal periods. DIII is expressed in neurons and degrades T4 and T3 to inactive metabolites. The action of T3 is mediated through nuclear receptors, which are expressed mainly in neurons. The receptors are ligand-modulated transcription factors, and a number of genes have been identified as regulated by thyroid hormone in brain. The regulated genes encode proteins of myelin, mitochondria, neurotrophins and their receptors, cytoskeleton, transcription factors, splicing regulators, cell matrix proteins, adhesion molecules, and proteins involved in intracellular signaling pathways. The role of thyroid hormone is to accelerate changes of gene expression that take place during development. Surprisingly, null-mutant mice for the T3 receptors show almost no signs of central nervous system involvement, in contrast with the severe effects of hypothyroidism. The resolution of this paradox is essential to understand the role of thyroid hormone and its receptors in brain development and function.

Overt and subclinical hypothyroidism complicating pregnancy

We studied the evolution of 150 pregnancies corresponding to 114 women (16-39 years old) with primary hypothyroidism. Fifty-one pregnancies (34%) were conceived under hypothyroidism: 16 overt (X +/- standard deviation [SD], thyroxine [T4]: 2.44 +/- 0.7 microg/dL; thyrotropin [TSH]: 33.4 +/- 8.82 mIU/L), and 35 subclinical hypothyroidism (T4: 6.93 +/- 1.88 microg/dL; TSH: 12.87 +/- 8.43 mIU/L); 99 pregnancies were conceived under euthyroidism while undergoing thyroid therapy. When treatment with levothyroxine was inadequate, the outcome of pregnancy was abortion in 60% of overtly hypothyroid patients and in 71.4% of subclinically hypothyroid patients, premature delivery in 20% and 7.2% respectively, and term delivery in 20% and 21.4%, respectively. When treatment was adequate, 100% of overtly hypothyroid patients and 90.5% of subclinically hypothyroid patients carried pregnancies to term; there were no abortions in any of the groups. Abortions, premature and term deliveries in patients who were euthyroid on levothyroxine at the time of conception were 4%, 11.1% and 84.9% respectively. Of the patients receiving levothyroxine therapy before conception, 69.5% had to increase the dose (mean increase 46.2 +/- 29.6 microg/d). Of 126 evaluated newborns, 110 were delivered at term while 16 were premature. Eight newborns, 4 were premature, had congenital malformations (6.3%), and 4 died. Our results show that the evolution of pregnancies did not depend on whether the hypothyroidism was overt or subclinical but mainly on the treatment received. The adequate treatment of hypothyroidism during gestation minimizes risks and generally, makes it possible for pregnancies to be carried to term without complications.

Thyroid size and iodine intake in iodine-repleted pregnant women in Isfahan, Iran

OBJECTIVE

To evaluate the goiter and iodine intake status of pregnant women in Isfahan, after 8 years of iodized salt distribution in Iran.

METHODS

Thyroid staging was assessed by clinical examination, thyroid volume was determined by sonography, and urinary iodine (UI) excretion was assessed by the digestion method in 90 healthy pregnant women (30 in each trimester) and 90 age-matched nonpregnant women selected by random sampling in prenatal and primary health-care clinics. The data were reported as mean +/- standard deviation; P values <0.05 were considered statistically significant.

RESULTS

The mean age of the pregnant and the nonpregnant women was 25.3 and 27.5 years, respectively-no significant difference (P = NS). The clinical goiter prevalence in the pregnant and the nonpregnant groups was 37% and 32%, respectively (P = NS). The mean thyroid volume in the pregnant and nonpregnant women was 7.8 +/- 3.2 and 7.8 +/- 2.8 mL, respectively (P = NS). Urinary iodine (UI) excretion was 20.7 +/- 6.9 mg/dL in pregnant women and 23.7 +/- 7.6 mg/dL in nonpregnant women (P = NS). The prevalence of goiter assessed by sonography was 29% in pregnant women and 21% in nonpregnant women (P = NS). The mean thyroid size in 26 of 90 pregnant women with goiter (thyroid volume >9.2 mL) was 11.8 +/- 2.73 mL and in 19 of 90 nonpregnant women with goiter was 12.36 +/- 1.6 mL (P = NS). The mean thyroid volume was 6.0 +/- 1.7, 9.9 +/- 1.7, 11.8 +/- 2.2, and 18.9 +/- 2.4 mL in the pregnant women with or without goiter at thyroid stages 0, Ia, Ib, and II, respectively. A strong correlation between goiter staging assessed by clinical examination and thyroid volume determined by sonography was found in pregnant (r = 0.77) and nonpregnant (r = 0.78) women (both P<0.000001). Mean UI excretion was 20.9 +/- 7.0, 19.9 +/- 6.8, 20.6 +/- 7.5, and 25.9 +/- 2.3 mg/dL in the pregnant women at thyroid stages 0, Ia, Ib, and II, respectively. In the pregnant and the nonpregnant women, no correlation was found between thyroid stage and UI excretion or between thyroid volume and UI excretion.

CONCLUSION

No iodine deficiency was found in Isfahani pregnant women. Thus, as in most iodine-sufficient areas, thyroid size did not increase during pregnancy. Despite sufficient iodine intake, a moderate prevalence of goiter was noted in pregnant and nonpregnant women. This study also revealed that careful physical examination of the thyroid had diagnostic accuracy similar to sonography.

Postpartum thyroiditis and autoimmune thyroiditis in women of childbearing age: recent insights and consequences for antenatal and postnatal care

Postpartum thyroiditis is a syndrome of transient or permanent thyroid dysfunction occurring in the first year after delivery and based on an autoimmune inflammation of the thyroid. The prevalence ranges from 5-7%. We discuss the role of antibodies (especially thyroid peroxidase antibodies), complement, activated T cells, and apoptosis in the outbreak of postpartum thyroiditis. Postpartum thyroiditis is conceptualized as an acute phase of autoimmune thyroid destruction in the context of an existing and ongoing process of thyroid autosensitization. From pregnancy an enhanced state of immune tolerance ensues. A rebound reaction to this pregnancy-associated immune suppression after delivery explains the aggravation of autoimmune syndromes in the puerperal period, e.g., the occurrence of clinically overt postpartum thyroiditis. Low thyroid reserve due to autoimmune thyroiditis is increasingly recognized as a serious health problem. 1) Thyroid autoimmunity increases the probability of spontaneous fetal loss. 2) Thyroid failure due to autoimmune thyroiditis-often mild and subclinical-can lead to permanent and significant impairment in neuropsychological performance of the offspring. 3) Evidence is emerging that as women age subclinical hypothyroidism-as a sequel of postpartum thyroiditis-predisposes them to cardiovascular disease. Hence, postpartum thyroiditis is no longer considered a mild and transient disorder. Screening is considered.

Prevalence of gestational thyrotoxicosis in Asian women evaluated in the 8th to 14th weeks of pregnancy: correlations with total and free beta human chorionic gonadotrophin

OBJECTIVES

The prevalence of gestational transient thyrotoxicosis (GTT) in Europeans evaluated during the 8th to 14th weeks of pregnancy is 2-3%. However, there is evidence that GTT may be more common in some Asian populations. The aims of this study were to evaluate the prevalence of thyroid hormone abnormalities in Asian women in their 8th to 14th weeks of pregnancy using highly sensitive free T4 and TSH assays and to correlate these with total and free beta-hCG levels.

DESIGN AND PATIENTS

One hundred and eighty-four consecutive unselected Asian (Singaporean) pregnant women seen at ante-natal clinics for the first time and who were in their 8th to 14th weeks of pregnancy were tested.

MEASUREMENTS

Serum free T4, free T3, TSH, total beta-hCG and free beta-HCG levels were measured on the Vitros ECi system (Johnson & Johnson Ortho-Clinical Diagnostics, Amersham, UK) which employs chemiluminescent immunochemical technology. This free T4 assay is free of biases related to serum binding capacity. The TSH assay used was a third generation assay. Thyrotrophin-receptor antibody (TRAb) levels were measured using LUMItest TRAK (BRAHMS Diagnostica, Berlin, Germany).

RESULTS

Two subjects (1.1%) were found to have Graves' disease. Elevated free T4, free T3, total T3 and suppressed TSH were seen in 14.8%, 3.3%, 26.4% and 33.0% of the remaining 182 pregnant women, respectively. Total and free beta-hCG correlated negatively with TSH (r = -0.30, P < 0.0001 and r = -0.29, P < 0.0001, respectively), positively with fT4 (r = 0.283, P < 0.001 and r = 0.253, P < 0.001) and fT3 (r = 0.273, P < 0.001 and r = 0.204, P < 0.01). 11.0% of cases had gestational thyrotoxicosis (GT) defined as elevated free T4 (> 19.1 pmol/l), suppressed TSH (< 0.36 mIU/l) and TRAb levels within the reference interval (0-0.9 U/l). The prevalence of GT was significantly higher in patients tested at 8-11 weeks compared to those evaluated at 12-14 weeks (14.4% vs. 4.7%, P < 0.05). Total beta-hCG (P = 0.0002), free beta-hCG (P < 0.0001) and free T4 (P = 0.02) levels were higher and TSH levels (P = 0.01) lower in patients tested at 8-11 weeks. Significant positive correlations between both total and free beta-hCG with free T4 were seen at 8-11 weeks but not in patients tested at 12 weeks or later. TT3 levels were similar in the two groups.

CONCLUSIONS

Using sensitive assays, the prevalence of gestational thyrotoxicosis in Asian women was found to be 11.0% and was significantly higher in subjects at 8-11 weeks of gestation than at 12-14 weeks. The positive correlation between hCG and free T4 seen in patients tested at 8-11 weeks was absent in patients tested at later stages of the first trimester. Future studies investigating the entity of gestational thyrotoxicosis, at least in Asian patients, should focus on patients at earlier stages of gestation than currently practised.

Iodine in human milk: perspectives for infant health

Iodine is essential for normal growth, mental development, and survival of infants. The main source of iodine for breastfeeding infants is the iodine found in human milk. Despite the importance of iodine for infant health, there have been limited studies addressing human milk iodine concentrations. The newly recommended Adequate Intake of iodine for infants is 110 microg/day for infants 0-6 months and 130 microg/day for infants 7-12 months. Further studies of human milk iodine are needed to ensure that iodine prophylaxis is providing sufficient iodine for mothers and infants worldwide.

Pregnancy and iodine

Hormonal changes and metabolic demands during pregnancy result in profound alterations in the biochemical parameters of thyroid function. For thyroid economy, the main events occurring during pregnancy are a marked increase in serum thyroxine-binding globulin levels; a marginal decrease in free hormone concentrations (in iodine-sufficient areas) that is significantly amplified when there is iodine restriction or overt iodine deficiency; a frequent trend toward a slight rise in basal thyrotropin (TSH) values between the first trimester and term; a transient stimulation of the maternal thyroid gland by elevated levels of human chorionic gonadotropin (hCG) resulting in a rise in free thyroid hormones and decrement in serum TSH concentrations during the first trimester; and finally, modifications of the peripheral metabolism of maternal thyroid hormones. Together, metabolic changes associated with the progression of gestation in its first half constitute a transient phase from preconception steady state to pregnancy steady state. In order to be met, these metabolic changes require an increased hormonal output by the maternal thyroid gland. Once the new equilibrium is reached, increased hormonal demands are maintained until term, probably through transplacental passage of maternal thyroid hormones and increased turnover of maternal thyroxine (T4), presumably under the influence of the placental (type 3) deiodinase. For healthy pregnant women with iodine sufficiency, the challenge of the maternal thyroid gland is to adjust the hormonal output in order to achieve the new equilibrium state, and thereafter maintain the equilibrium until term. In contrast, the metabolic adjustment cannot easily be reached during pregnancy when the functional capacity of the thyroid gland is impaired because of iodine deficiency. The ideal dietary allowance of iodine recommended by World Health Organization (WHO) is 200 microg of iodine per day for pregnant women. In conditions with iodine restriction, enhanced thyroidal stimulation is revealed by relative hypothyroxinernia and goitrogenesis. Goiters formed during gestation may only partially regress after parturition. Pregnancy, therefore, represents one of the environmental factors that may help explain the higher prevalence of goiter and thyroid disorders in women compared with men. An iodine-deficient status in the mother also leads to goiter formation in the progeny and neuropsycho-intellectual impairment in the offspring. When adequate iodine supplementation is given early during pregnancy, it allows for the correction and almost complete prevention of maternal and neonatal goitrogenesis. In summary, pregnancy is accompanied by profound alterations in the thyroid economy, resulting from a complex combination of factors specific to the pregnant state, which together concur to stimulate the maternal thyroid machinery. Increased thyroidal stimulation induces, in turn, a sequence of events leading from physiological adaptation of the thyroidal economy observed in healthy iodine-sufficient pregnant women to pathological alterations affecting both thyroid function and the anatomical integrity of the thyroid gland, when gestation takes place in conditions with iodine restriction or deficiency: the more severe the iodine deficiency, the more obvious, frequent, and profound the potential maternal and fetal repercussions.

Management of a pregnant patient with Graves' disease complicated by thionamide-induced neutropenia in the first trimester

A 31-year-old woman presented with neutropenia due to thionamide drug therapy for Graves' disease. She also reported 8 weeks of amenorrhoea and had a positive pregnancy test. Her drug therapy was discontinued and her neutropenia resolved uneventfully. The hyperthyroidism recurred a week later. After consideration of all treatment options, it was decided to observe until 14 weeks when an elective thyroidectomy was planned. Mother and fetus were monitored closely and both tolerated moderate hyperthyroidism well. At 14 weeks the patient underwent a total thyroidectomy after rendering her euthyroid with a short course of sodium ipodate. Labour was induced at 41 weeks. Delivery was complicated by fetal distress and precipitated a forceps delivery. A 3250 g male infant was born with poor Apgar score and required 2 h of ventilation. At 1 year, the child had reached all developmental milestones at appropriate times. Both mother and fetus may tolerate moderate thyrotoxicosis well in early pregnancy, an alternative that should be considered when thionamide drug therapy is contraindicated.

Effects of amiodarone administration during pregnancy on neonatal thyroid function and subsequent neurodevelopment

Amiodarone, a benzofuranic derivative, iodine-rich drug, has been used in pregnancy for either maternal or fetal tachyarrhythmias. Amiodarone, its main metabolite (desethylamiodarone) and iodine are transferred, albeit incompletely, through the placenta, resulting in a relevant fetal exposure to the drug and iodine overload. Since the fetus acquires the capacity to escape from the acute Wolff-Chaikoff effect only late in gestation, the iodine overload may cause fetal/neonatal hypothyroidism and goiter. Among the reported 64 pregnancies in which amiodarone was given to the mother, 11 cases (17%) of hypothyroidism in the progeny (10 detected at birth, 1 in utero) were reported, 9 non-goitrous (82%) and 2 (18%) associated with goiter. Hypothyroidism was transient in all cases, and only 5 infants were treated short-term with thyroid hormones. Only 2 newborns had transient hyperthyroxinemia, associated with low serum TSH concentrations in one. Neurodevelopment assessment of the hypothyroid infants, when carried out, showed in some instances mild abnormalities, most often reminiscent of the Non-verbal Learning Disability Syndrome; however, these features were also reported in some amiodarone-exposed euthyroid infants, suggesting that there might be a direct neurotoxic effect of amiodarone during fetal life. Breast-feeding was associated with a substantial ingestion of amiodarone by the infant, but in the few cases followed it did not cause changes in the newborn's thyroid function. In conclusion, amiodarone therapy during pregnancy may cause fetal/neonatal hypothyroidism and, less frequently, goiter. Thus, the use of amiodarone in pregnancy should be limited to maternal/fetal tachyarrhythmias which are resistant to other drugs or life-threatening. If amiodarone is used during gestation, a careful fetal/neonatal evaluation of thyroid function and morphology is warranted. It seems prudent to advise that fetal/neonatal hypothyroidism be treated, as soon as the diagnosis is made, even in utero, to avoid neurodevelopment abnormalities, although the latter may occur independently of hypothyroidism. If breast-feeding is allowed, careful evaluation of the infant's thyroid function and morphology is required because of the continuing exposure of the infant to the drug.

Goitrogenesis during pregnancy and neonatal hypothyroxinaemia in a borderline iodine sufficient area

OBJECTIVE

Severe iodine deficiency disorders (IDDs) may have been eradicated in many parts of the world, but milder forms still exist and may escape detection. We evaluated the impact of pregnancy on the maternal and fetal thyroid axis in Hong Kong, a coastal city in southern China with borderline iodine intake.

DESIGN

A prospective study performed in a maternity hospital.

PATIENTS

Two hundred and thirty pregnant women were prospectively studied and their neonates assessed at birth.

MEASUREMENTS

Urine iodine concentration, thyroid function tests and thyroid volume (TV) by ultrasound were determined in the mothers during pregnancy and up to 3 months postpartum and in the neonates.

RESULTS

Increased urinary iodine concentration was seen from first trimester onwards and the proportion of women having urine iodine concentration of < 0.4 micromol/l decreased from 11.3% in the first trimester to 4.7% in the third trimester. There was progressive reduction in circulating fT4 and fT3 concentrations and free thyroxine index (FTI) with increasing gestation and the percentage of women having subnormal levels at term were 53.2%, 61.1% and 4.8%, respectively. The serum TSH concentration during pregnancy doubled towards term. In the first trimester, multiparous women had significantly larger TV than the nulliparous women (P < 0.001). By the third trimester, TV had increased by 30% (range 3-230%) so that the goitre incidence was 14.1%, 21.8%, 25.9% during the three trimesters of pregnancy, and 24.3% and 21.9% at 6 weeks and 3 months postpartum (ANOVA, P < 0.05). The change in thyroid volume during pregnancy correlated positively with the change in thyroglobulin (r = 0.225, P < 0.002) and negatively with urinary iodine concentration (r = - 0.149, P < 0.02). Fourteen women with excessive thyroidal stimulation in the second trimester (defined as those with thyroglobulin (Tg) concentrations in the highest tertile and FTI in the lowest tertile) were found to have lower urine iodine concentrations and larger TV (both P < 0.005) throughout pregnancy, and their neonates had higher cord TSH (P < 0.05), Tg (P < 0.05) and slightly larger TV (P = 0.06) as compared to the findings in 216 pregnant women without evidence of thyroid stimulation. Seven neonates (50%) born to these women had subnormal fT4 levels at birth.

CONCLUSION

In a borderline iodine sufficient area, pregnancy posed an important stress resulting in higher rates of maternal goitrogenesis as well as neonatal hypothyroxinaemia and hyperthyro- trophinaemia. An adequate iodization program is necessary to eliminate iodine deficiency disorders during pregnancy.

Thyroidopathies

Pregnancy affects thyroid physiology in many ways: (a) The renal iodide clearance rate is increased, hence iodine requirements increase. (b) The fetal requirements for thyroid hormones and iodide are an additional problem. (c) Serum thyroxine-binding globulin increases, thus producing an increase in the levels of total T4 and T3. (d) Chorionic gonadotropin has a thyroid-stimulating activity. This may be compensated for by a decrease in TSH, but in some cases gestational thyrotoxicosis occurs. (e) Thyroid autoimmunity usually subsides during pregnancy, but may rebound a few months after parturition, and postpartum thyroiditis may occur. Because maternal antithyroid autoantibodies cross the placenta readily, fetal and neonatal hyperthyroidism (or hypothyroidism) may develop. Pre-existing thyroid diseases are influenced. Nontoxic goiter increases in size. Iodine and/or thyroxine may be required. Graves' disease may remit. If present, antithyroid drugs should be given in small doses, and quite often they may be stopped altogether. Hypothyroid patients may require a larger T4 dose.

Thyroid peroxidase antibodies in Mexican-born healthy pregnant women, in women with type 2 or gestational diabetes mellitus, and in their offspring

OBJECTIVE

To search for differences in the frequency of thyroid peroxidase antibodies (TPO-Ab) among 150 pregnant Mexican women who were healthy, had type 2 diabetes mellitus (DM), or had gestational diabetes mellitus (GDM).

METHODS

Fifty healthy women, 50 women with type 2 DM, and 50 women with GDM were studied at delivery. In addition, 142 of their offspring were included in the study. TPO-Ab were determined by enzyme immunoassay, and total triiodothyronine, free thyroxine, and thyroid-stimulating hormone (thyrotropin) were measured by radioimmunoanalysis.

RESULTS

TPO-Ab were < or = 70 U/mL (negative) in 50% of the healthy women and in 60% and 60% of women with type 2 DM and GDM, respectively (no significant difference). TPO-Ab were 71 to 250 U/mL (slightly positive) in 40% of healthy women and in 30% and 34% of women with type 2 DM and GDM, respectively (no significant difference). TPO-Ab were > or =251 U/mL (strongly positive) in 10% of healthy women and in 10% and 6% of women with type 2 DM and GDM, respectively. One healthy woman had subclinical hypothyroidism, and the rest were euthyroid. The newborn offspring of these Mexican women were euthyroid and had similar frequencies of TPO-Ab (all had TPO-Ab <250 U/mL).

CONCLUSION

(1) The frequency of TPO-Ab > or =251 U/mL was similar in pregnant Mexican women with GDM in comparison with those who were healthy or had type 2 DM. (2) The similar high frequencies of slightly positive TPO-Ab in the three groups of pregnant women can partially be explained by the existence of an ethnic factor, the very strong family history of DM in a substantial percentage of them, and the use of a more sensitive and specific assay for detection of TPO-Ab.

The role of iodine in brain development

I is required for the synthesis of thyroid hormones. These hormones, in turn, are required for brain development, which occurs during fetal and early postnatal life. The present paper reviews the impact of I deficiency (1) on thyroid function during pregnancy and in the neonate, and (2) on the intellectual development of infants and children. All extents of I deficiency (based on I intake (microgram/d); mild 50-99, moderate 20-49, severe > 20) affect the thyroid function of the mother and neonate, and the mental development of the child. The damage increases with the extent of the deficiency, with overt endemic cretinism as the severest consequence. This syndrome combines irreversible mental retardation, neurological damage and thyroid failure. Maternal hypothyroxinaemia during early pregnancy is a key factor in the development of the neurological damage in the cretin. Se deficiency superimposed on I deficiency partly prevents the neurological damage, but precipitates severe hypothyroidism in cretins. I deficiency results in a global loss of 10-15 intellectual quotient points at a population level, and constitutes the world's greatest single cause of preventable brain damage and mental retardation.

Decrease of free thyroxine levels after controlled ovarian hyperstimulation

Controlled ovarian hyperstimulation could lead to opposing effects on thyroid function. Therefore, in a prospective study of 65 women undergoing controlled ovarian hyperstimulation, thyroid hormones, T4-binding globulin, TPO antibodies, gonadotropins, estradiol, and PRL were measured before and after controlled ovarian hyperstimulation. After ovarian stimulation (mean +/- SE of mean): free T4 decreased, 14.4 +/- 0.2 vs. 12.9 +/- 0.2 pmol/L (P < 0.0001); thyroid-stimulating hormone increased, 2.3 +/- 0.3 vs. 3.0 +/- 0.4 mU/L (P < 0.0001); T4-binding globulin increased, 25.2 +/- 0.7 vs. 33.9 +/- 0.9 mg/L (P < 0.0001); total T4 increased, 98.1 +/- 2.3 vs. 114.6 +/- 2.5 nmol/L (P < 0.0001); total T3 increased, 2.0 +/- 0.04 vs. 2.3 +/- 0.07 nmol/L (P < 0.0001); TPO antibodies decreased, 370 +/- 233 U/mL vs. 355 +/- 224 U/mL (P < 0.0001); LH decreased, 8.1 +/- 1.1 vs. 0.4 +/-0.1 U/L (P < 0.0001); FSH did not change, 6.5 +/- 0.6 vs. 7.9 +/- 0.9 U/L (P = 0.08); human CG increased, <2 +/- 0.0 vs. 195 +/- 16 U/L (P < 0.0001); estradiol increased, 359.3 +/- 25.9 pmol/L vs. 3491.8 +/-298.3 pmol/L (P < 0.0001); and PRL increased, 0.23 +/- 0.02 vs. 0.95 +/- 0.06 U/L (P < 0.0001). Because low maternal free T4 and elevated maternal thyroid-stimulating hormone levels during early gestation have been reported to be associated with impaired psychomotor development in the offspring, our findings indicate the need for additional studies in the children of women who where exposed to high levels of estrogens around the time of conception.

Thyroglobulin in serum as an indicator of iodine status during pregnancy

Serum thyroglobulin and thyrotropin as well as urinary iodine concentrations were measured in healthy, pregnant Swedish (n=27) and Sudanese (n=21) women and the results compared with those of healthy Swedish (n=14) and Sudanese (n=20) non-pregnant controls. The median thyroglobulin concentrations (and interquartile range) in the Swedish pregnant women for the three trimesters were 15.5 (8-24), 10.5 (7-19) and 18.0 (13-25) microg/L, respectively. The median third trimester concentration was higher than both the first and second trimester concentrations, respectively (p<0.0001, p<0.0001). Compared to the control group, the Swedish pregnant women had a significantly higher median thyroglobulin concentration in the third trimester (p<0.05). Among the Sudanese pregnant women, the median serum thyroglobulin concentrations (and interquartile range) were 27.5 (12-40), 25.0 (15-43) and 30.0 (15-67) microg/L during the first, second and third trimesters, respectively. There were no significant differences between these concentrations. Compared to the control group, the Sudanese pregnant women had a significantly higher median thyroglobulin in the third trimester (p<0.01). The Sudanese pregnant women also showed significantly higher median thyroglobulin concentrations than the Swedish pregnant women in all the three trimesters of pregnancy (p<0.05, p<0.001 and p<0.01, respectively). However, there were no significant differences between the two non-pregnant controls. Among the Swedish pregnant women, 40%, 23% and 30% of the subjects showed serum thyroglobulin concentrations above 20 microg/ L during the first, second and third trimesters of pregnancy, respectively. Corresponding figures for the Sudanese pregnant women were 55%, 61% and 64%, respectively. A significantly negative correlation was shown between serum thyroglobulin and urinary iodine concentrations during the second and third trimesters in the Swedish women (r= -0.8, p=0.01 and r= -0.5, p=0.03, respectively), and in the third trimester in the Sudanese women (r= -0.6, p=0.03). No such correlation was observed between thyrotropin and urinary iodine concentration in either the Swedish or the Sudanese pregnant women. It is concluded that serum thyroglobulin is a more sensitive indicator of iodine deficiency than serum thyrotropin during pregnancy.

Thyroid Function during Pregnancy

Background: This Case Conference reviews the normal changes in thyroid activity that occur during pregnancy and the proper use of laboratory tests for the diagnosis of thyroid dysfunction in the pregnant patient.

Case: A woman in the 18th week of pregnancy presented with tachycardia, increased blood pressure, severe vomiting, increased total and free thyroid hormone concentrations, a thyroid-stimulating hormone (TSH) concentration within the reference interval, and an increased human chorionic gonadotropin (hCG) β-subunit concentration.

Issues: During pregnancy, normal thyroid activity undergoes significant changes, including a two- to threefold increase in thyroxine-binding globulin concentrations, a 30–100% increase in total triiodothyronine and thyroxine concentrations, increased serum thyroglobulin, and increased renal iodide clearance. Furthermore, hCG has mild thyroid stimulating activity. Pregnancy produces an overall increase in thyroid activity, which allows the healthy individual to remain in a net euthyroid state. However, both hyper- and hypothyroidism can occur in pregnant patients. In addition, two pregnancy-specific conditions, hyperemesis gravidarum and gestational trophoblastic disease, can lead to clinical hyperthyroidism. The normal changes in thyroid activity and the association of pregnancy with conditions that can cause hyperthyroidism necessitates careful interpretation of thyroid function tests during pregnancy.

Conclusion: Assessment of thyroid function during pregnancy should be done with a careful clinical evaluation of the patient’s symptoms as well as measurement of TSH and free, not total, thyroid hormones. Measurement of thyroid autoantibodies may also be useful in selected cases to detect maternal Graves disease or Hashimoto thyroiditis and to assess risk of fetal or neonatal consequences of maternal thyroid dysfunction.

Stimulation of Chinese hamster ovary cells expressing human thyrotropin receptors by serum human chorionic gonadotropin of patients with hydatidiform mole

We evaluated the stimulation of Chinese hamster ovary cells expressing human thyrotropin receptors (CHO-hTSHR cell) by sera of five patients with hydatidiform mole before and after the evacuation of the mole, and compared the results with serum human chorionic gonadotropin (hCG) concentrations and serum free thyroid hormones in these patients. Significantly increased CHO-hTSHR cell stimulating activities were observed in sera from untreated patients, and the activity decreased promptly after the evacuation of the mole, concomitantly with the decrease in serum hCG and free thyroid hormones. CHO-hTSHR cell stimulating activity of sera of the untreated patients significantly correlated with serum hCG. Moreover, serum hCG stimulated CHO-hTSHR cells in a dose dependent manner similar to the dose-response curve of the stimulation by purified hCG. Sera of the patients and purified hCG did not stimulate nontransfected CHO-K1 cells. However, a significant correlation was not observed between serum-free thyroid hormones and serum hCG or between serum free thyroid hormones and CHO-hTSHR cell stimulating activities in untreated patients. These results indicate that serum hCG from patients with hydatidiform mole stimulates thyroid gland by interacting with TSH receptors, and suggest that the increase in thyroid hormones in patients may depend on both the increased serum hCG and the responsiveness of their thyroid glands to hCG.

Estradiol increases proliferation and down-regulates the sodium/iodide symporter gene in FRTL-5 cells

Goiter (increased thyroid gland size) is more prevalent in women than men, even in areas where iodine levels in the diet are sufficient. We investigated a possible role of estrogen on thyroid follicular cell growth using rat FRTL-5 thyroid follicular cells as a model. Estrogen receptor-alpha (ERalpha) messenger RNA was present in FRTL-5 cells using a RT-PCR assay and was confirmed by Western blot analysis. An estrogen-responsive reporter gene was transfected into FRTL-5 cells to test the functionality of the endogenous ERs. Estradiol increased the activity of the reporter gene, and the antagonist, ICI182780, inhibited ER-dependent transcription. To extend this analysis, we examined the effect of estradiol on FRTL-5 cell growth. Estradiol increased FRTL-5 cell growth in a time- and concentration-dependent manner in either the absence or presence of TSH. Because iodine is known to inhibit thyroid cell growth, the effect of estradiol on the expression of the sodium/iodide symporter (NIS) was assessed as a potential target of estrogen action. Estradiol blocked TSH-induced NIS expression, and treatment of cells with estradiol and ICI182780 restored TSH-induced NIS expression to normal levels. These data demonstrate that FRTL-5 cells contain functional ERs that enhance cell growth and inhibit expression of the NIS. The demonstration of a direct effect of estradiol on thyroid follicular cells raises the possibility that it may play a role in the sexually dimorphic prevalence of goiter.

Successful outcome of pregnancy in a thyroidectomized-parathyroidectomized young woman affected by severe hypothyroidism

Severe hypothyroidism was discovered in a young woman in her 29th week of pregnancy. Previously, at the age of 12 years, she had undergone thyroid surgery for Graves' disease that resulted in persistent hypothyroidism and hypoparathyroidism. After surgical excision, the patient started levothyroxine replacement therapy and had regular control of thyroid function with normal findings throughout the years. The dose of levothyroxine had not been adjusted when the pregnancy started, and at the 29th week of gestation the patient had a thyrotropin (TSH) of 72.4 microU/mL. Ultrasound studies were performed in order to monitor fetal development. The fetal parameters analyzed before the adjustment of levothyroxine therapy showed growth retardation of various degrees. All analyzed fetal parameters (biparietal diameter, cranial and abdominal circumference, humerus and femur length) improved during the last 6 weeks of gestation, showing a good correlation with the newly achieved euthyroid state of the mother. The infant was clinically euthyroid at birth and was found normal at all evaluations of the neonatal hypothyroidism screening program (1, 5, 30 days).

Maternal hypothyroidism: recognition and management

Women with compensated early thyroid failure, or those from areas of reduced iodine intake, may first be found to be hypothyroid during pregnancy. In women with previously diagnosed hypothyroidism already on thyroxine (T4) replacement therapy, pregnancy is often associated with an increased dose requirement. The mechanism producing this increased requirement is not known, but it is likely to be the result of a number of factors that may differ depending on the stage of pregnancy. An increased T4 dose requirement is typically seen by the first trimester, can continue to increase throughout pregnancy, and reverts to the prepregnancy dose requirement after delivery. The magnitude of the increased T4 requirement is related to the etiology of hypothyroidism. Monitoring thyroid status and adjusting the T4 dose during pregnancy is a challenge due to changes in T4 metabolism throughout pregnancy.

Acidic isoforms of chorionic gonadotrophin in European and Samoan women are associated with hyperemesis gravidarum and may be thyrotrophic

OBJECTIVE

There is conflicting evidence concerning the role of human chorionic gonadotrophin (hCG) in the aetiology of hyperemesis gravidarum (HG); particular isoforms of hCG may be the critical factor. Ethnic differences in HG prevalence and putative thyrotrophic effects of hCG may also relate to differences in hCG isoform profiles. To address these issues we examined the relationship of hCG isoforms to HG and thyroid function tests in two groups of women from ethnic backgrounds with significantly different HG prevalence rates.

PATIENTS AND DESIGN

We enrolled 10 European and 10 Samoan women with HG and an equally sized non-hyperemetic, gestational stage matched control group.

MEASUREMENTS

We administered a questionnaire, generated serum hCG charge-isoform profiles by chromatofocusing and measured the serum concentrations of total hCG, oestradiol (E2), thyrotrophin (TSH) and free thyroxine (FT4).

RESULTS

The mean serum total hCG levels were highest in the Samoan hyperemetics (176,268 IU/l), and overall higher in hyperemetics compared with controls (159,770 IU/l vs. 86,420 IU/l, P < 0.001). When compared with controls, hyperemetics displayed increased hCG concentrations in the more acidic half (pH < 4) of the chromatofocusing pH range (89,843 IU/l vs. 41,146 IU/l, P < 0.003). Serum E2 levels did not differ between the four groups, but correlated with the hCG concentration between pH 5.2 and 4.01. Mean serum TSH levels were significantly lower in hyperemetics than in controls (0.33 mIU/l vs. 1.19 mIU/l, P < 0.001) and correlated with the hCG concentration between pH 4.6 and 2.8, while serum FT4 correlated with the hCG concentration below pH 4.0.

CONCLUSIONS

Acidic isoforms of hCG may play a role in the aetiology of HG and gestational thyrotoxicosis. Minor ethnic differences in hCG isoform profiles were observed, but the relationship of acidic hCG isoforms to HG and serum thyroid hormone levels was largely independent of the patients' ethnicity. The mechanisms by which acidic isoforms might provoke nausea remain uncertain, but do not seem to involve E2, while the longer half-life of acidic hCG isoforms may result in increased in vivo TSH receptor cross-talk with resultant thyrotrophic effects.

Pregnant rat uterus expresses high levels of the type 3 iodothyronine deiodinase

Although thyroid hormones are critically important for the coordination of morphogenic processes in the fetus and neonate, premature exposure of the embryo to levels of the hormones present in the adult is detrimental and can result in growth retardation, malformations, and even death. We report here that the pregnant rat uterus expresses extremely high levels of the type 3 iodothyronine deiodinase (D3), which inactivates thyroxine and 3,3', 5-triiodothyronine by 5-deiodination. Both D3 mRNA and activity were present at the implantation site as early as gestational day 9 (E9), when expression was localized using in situ hybridization to uterine mesometrial and antimesometrial decidual tissue. At later stages of gestation, uterine D3 activity remained very high, and the levels exceeded those observed in the placenta and in fetal tissues. After days E12 and E13, as decidual tissues regressed, D3 expression became localized to the epithelial cells lining the recanalized uterine lumen that surrounds the fetal cavity. These findings strongly suggest that the pregnant uterus, in addition to the placenta, plays a critical role in determining the level of exposure of the fetus to maternal thyroid hormones.

Thyroid hyperfunction during pregnancy

The present report focuses on the two main causes of hyperthyroidism observed in the pregnant state: Graves' disease (GD) and gestational transient thyrotoxicosis. Together, the prevalence of hyperthyroidism may represent 3% to 4% of all pregnancies, and therefore constitutes an important clinical issue. Concerning GD, the variable presentations of the disease (women under treatment, in remission, or considered cured) and specific alterations occurring in pregnancy are discussed: changes in thyrotropin (TSH) receptor antibody titers, the risk of fetal and neonatal thyrotoxicosis, the outcome of pregnancy in relation to the control of hyperthyroidism, and the treatment of active GD during and after pregnancy with antithyroid drugs. Gestational transient thyrotoxicosis is associated with a direct stimulation of the maternal thyroid gland by human chorionic gonadotropin (hCG), and has been shown to be directly related to both the amplitude and duration of peak hCG values. The syndrome is usually transient, observed at the end of the first trimester, and is frequently associated with emesis. Finally, we propose a global strategy for the systematic screening of hyperthyroidism during pregnancy, based on an algorithm that allows for the diagnosis of both autoimmune and nonautoimmune forms of hyperthyroidism in the pregnant state.