Overt and subclinical hypothyroidism complicating pregnancy

Optimal thyrotropin level: normal ranges and reference intervals are not equivalent

This paper marshals arguments in support of a narrower, optimal or true normal range for thyrotropin (TSH) of 0.4 to 2.5 mIU/L, based on clinical results and recent information on the relatively stable and narrow range of values in patients without thyroid disease. The terminology used for TSH results is clarified in an attempt to help physicians interpret, explain, and respond to TSH test results for their patients.

Outcomes of pregnancy complicated by thyroid disease

AIMS

To perform a case note review of pregnancies complicated by thyroid dysfunction to determine management and therapeutic intervention in relation to pregnancy outcome.

METHODS

A retrospective case note analysis of 81 ongoing pregnancies in 70 pregnant women with a history of thyroid dysfunction over a period of 5 years at the Glasgow Royal Maternity Hospital (GRMH), Glasgow, Scotland, United Kingdom. The results of thyroid function tests and whether a change in treatment was instituted were recorded. Thyroid function was assessed by standard laboratory reference ranges for free thyroxine (FT4) and thyroid stimulating hormone (TSH) in all trimesters. Other parameters were also noted.

RESULTS

Medication levels needed to be increased in the hypothyroid group (45%), and decreased (38%) in the hyperthyroid group.

CONCLUSION

Pregnancy outcome was good in majority of cases given appropriate replacement therapy for stated reference values.

Recurrent miscarriage

Recurrent miscarriage, the occurrence of three consecutive first-trimester losses of pregnancy, affects 1% of women. The purported causes of recurrent miscarriage include chromosomal abnormalities, thrombophilia, metabolic disorders, anatomical causes and immune factors. At present, the only recommended investigations are testing for lupus anticoagulant and anticardiolipin antibody levels (to diagnose antiphospholipid syndrome, an acquired thrombophilia) and the karyotyping of both parents for chromosomal abnormalities. Women with antiphospholipid syndrome should be offered treatment with aspirin and low molecular weight heparin. Couples with chromosomal abnormalities should be referred to a clinical geneticist with whom the options of prenatal diagnosis, pre-implantation genetic diagnosis, donor gametes and adoption in subsequent pregnancies should be discussed. Couples with unexplained recurrent miscarriage should be offered appropriate emotional support and reassurance that they have a good prognosis for future pregnancies.

The thyroid and pregnancy: a novel risk factor for very preterm delivery

The major cause of neonatal mortality and morbidity is preterm delivery in general (< 37 completed weeks), and especially very preterm delivery (< 32 completed weeks). The objective of this study is to determine if either thyroid hormonal dysfunction and/or the presence of thyroid autoantibodies in the mother are associated with an increased risk of preterm and/or very preterm delivery. Data were collected prospectively and analyzed as a nested-case control study. There were 953 delivered gravidas enrolled between 1996 and 2002. Samples were collected at entry to care and stored at -70 degrees C. Cases included all women with preterm delivery (n = 124). Controls (n = 124) were randomly selected from among the 829 women who delivered at term (> 37 completed weeks). All samples were assessed for thyroid stimulating hormone, thyroperoxidase antibody, and thyroglobulin antibody. Gravidas with high thyrotropin (TSH) levels had a greater than threefold increase in risk of very preterm delivery. In some analyses, gravidas who tested positive for thyroglobulin antibody at entry to prenatal care also had a better than twofold increased risk of very preterm delivery. There were no significant associations between TSH level or thyroglobulin antibody positivity and the risk of moderately preterm delivery.

Is thyroid inadequacy during gestation a risk factor for adverse pregnancy and developmental outcomes?

A workshop entitled, "The Impact of Maternal Thyroid Diseases on the Developing Fetus: Implications for Diagnosis, Treatment, and Screening," was held in Atlanta, Georgia, January 12-13, 2004. This paper reports on the individual session that examined thyroid inadequacy during gestation as a risk factor for adverse pregnancy and developmental outcomes. For this session the following papers were presented: "Adverse Pregnancy Outcomes"; "Thyroid Physiology in the Fetus"; "New England Data: Cretinism Revisited-Preventing Fetal Brain Damage when Mothers Have Subclinical Hypothyroidism"; "Dutch Data: Pregnancy, Maternal Thyroid (Dys)function and Outcome of the Offspring"; and "Report on the Wales Controlled Antenatal Thyroid Screening Study (CATS); A Prospective RCT." These presentations were formally discussed by invited respondents well as others in attendance. Salient points from this session about which there was agreement include the following. Maternal hypothyroidism is associated with complications of pregnancy and adverse effects on the fetus. These risks are greater in women with overt hypothyroidism compared to subclinical hypothyroidism, and also appear to be increased in women with euthyroid autoimmune thyroid disease. If maternal hypothyroidism is treated adequately, this appears to reduce the risk for adverse outcomes. The demonstration of a pattern of ontogeny of fetal cerebral cortex deiodinases and thyroid hormone receptors, beginning by 7-8 weeks' gestation, is circumstantial evidence that thyroid hormone plays an important role in fetal neurodevelopment. Significant fetal thyroid hormone production and secretion does not begin until approximately 20 weeks' gestation. If there is a significant role for thyroid hormone in fetal neurodevelopment before 20 weeks' gestation, it likely is of maternal origin. Studies demonstrate low levels of thyroxine in the fetal coelomic fluid and blood prior to 12-14 weeks' gestation. Published data consistently document a relationship between maternal thyroid deficiency during pregnancy and problems with neuropsychological development of the offspring.

Are detection and treatment of thyroid insufficiency in pregnancy feasible?

A workshop entitled, "The Impact of Maternal Thyroid Diseases on the Developing Fetus: Implications for Diagnosis, Treatment, and Screening," was held in Atlanta, Georgia, January 12-13, 2004. The workshop was sponsored jointly by The National Center on Birth Defects and Developmental Disabilities of The Centers for Disease Control and Prevention (CDC) and The American Thyroid Association. This paper reports on the individual session that examined the ability to detect and treat thyroid dysfunction during pregnancy. For this session, presented papers included: "Laboratory Reference Values in Pregnancy" and "Criteria for Diagnosis and Treatment of Hypothyroidism in Pregnancy." These presentations were formally discussed by invited respondents and by others in attendance. Salient points from this session about which there was agreement include the following: thyrotropin (TSH) can be used as marker for hypothyroidism in pregnancy, except when there is iodine deficiency usually evidenced by elevated serum thyroglobulin (Tg). We need more longitudinal studies of TSH during pregnancy in iodine-sufficient populations without evidence of autoimmune thyroid disease to develop trimester-specific TSH reference ranges. Current free thyroxine (FT4) estimate methods are sensitive to abnormal binding-protein states such as pregnancy. There is no absolute FT4 value that will define hypothyroxinemia across methods. Total thyroxine (TT4) changes in pregnancy are predictable and not method-specific. TT4 below 100 nmol/L (7.8 microg/dL) is a reasonable indicator of hypothyroxinemia in pregnancy. Women with known hypothyroidism and receiving levothyroxine (LT4) before pregnancy should plan to increase their dosage by 30% to 60% early in pregnancy. Women with autoimmune thyroid disease prior to pregnancy are at increased risk for thyroid insufficiency during pregnancy and postpartum thyroiditis and should be monitored with TSH during pregnancy.

The Role of Thyroid Hormone in Trophoblast Function, Early Pregnancy Maintenance, and Fetal Neurodevelopment

OBJECTIVE

To review the literature on the roles of thyroid hormone in trophoblast function, early pregnancy maintenance, and fetal neurodevelopment.

METHODS

MEDLINE was searched for English-language papers published from 1971 to 2003, using the key words "brain," "hypothyroidism," "placenta," "pregnancy," "threatened abortion," "thyroid hormone," "thyroid hormone receptor," "thyroid hormone replacement therapy," "thyroid hormone-responsive gene," and "trophoblast."

RESULTS

Transplacental transfer of thyroid hormone occurs before the onset of fetal thyroid hormone secretion. Thyroid hormone receptors and iodothyronine deiodinases are present in the placenta and the fetal central nervous system early in pregnancy, and thyroid hormone plays a crucial role both in trophoblast function and fetal neurodevelopment. Maternal hypothyroxinemia is associated with a high rate of spontaneous abortion and long-term neuropsychological deficits in children born of hypothyroid mothers. Maternal iodine deficiency also causes a wide spectrum of neuropsychological disorders in children, ranging from subclinical deficits in cognitive motor and auditory functions to hypothyroid-induced cognitive impairment in infants. However, these conditions are preventable when iodine supplementation is initiated before the second trimester. Although thyroid hormone replacement therapy is effective for reducing the adverse effects complicated by maternal hypothyroidism, the appropriate dose of thyroid hormone is mandatory in protecting the early stage of pregnancy.

CONCLUSIONS

Close monitoring of maternal thyroid hormone status and ensuring adequate maternal thyroid hormone levels in early pregnancy are of great importance to prevent miscarriage and neuropsychological deficits in infants.

Timing and magnitude of increases in levothyroxine requirements during pregnancy in women with hypothyroidism

BACKGROUND

Hypothyroidism during pregnancy has been associated with impaired cognitive development and increased fetal mortality. During pregnancy, maternal thyroid hormone requirements increase. Although it is known that women with hypothyroidism should increase their levothyroxine dose during pregnancy, biochemical hypothyroidism occurs in many. In this prospective study we attempted to identify precisely the timing and amount of levothyroxine adjustment required during pregnancy.

METHODS

Women with hypothyroidism who were planning pregnancy were observed prospectively before and throughout their pregnancies. Thyroid function, human chorionic gonadotropin, and estradiol were measured before conception, approximately every two weeks during the first trimester, and monthly thereafter. The dose of levothyroxine was increased to maintain the thyrotropin concentration at preconception values throughout pregnancy.

RESULTS

Twenty pregnancies occurred in 19 women and resulted in 17 full-term births. An increase in the levothyroxine dose was necessary during 17 pregnancies. The mean levothyroxine requirement increased 47 percent during the first half of pregnancy (median onset of increase, eight weeks of gestation) and plateaued by week 16. This increased dose was required until delivery.

CONCLUSIONS

Levothyroxine requirements increase as early as the fifth week of gestation. Given the importance of maternal euthyroidism for normal fetal cognitive development, we propose that women with hypothyroidism increase their levothyroxine dose by approximately 30 percent as soon as pregnancy is confirmed. Thereafter, serum thyrotropin levels should be monitored and the levothyroxine dose adjusted accordingly.

Hypothyroidism and chronic autoimmune thyroiditis in the pregnant state: maternal aspects

Hypothyroidism during pregnancy is associated with adverse outcomes that can be ameliorated or prevented by adequate therapy with thyroxine. Currently, there are no guidelines for universal screening for thyroid dysfunction in pregnant women or in women of reproductive age. Therefore, it is important to recognize those groups of women who may be at higher risk for development of hypothyroidism so that serum TSH testing may be performed with appropriate initiation of thyroxine therapy. In addition, the thyroxine therapy of women with established hypothyroidism should be optimized prior to conception and during pregnancy when the thyroxine dosage requirement generally increases early in gestation. The diverse etiologies of maternal hypothyroidism may require different increments in thyroxine dose during pregnancy, and generally the postpartum dosage requirement returns to pre-pregnancy levels.

Cardiovascular and medical ramifications of treatment of subclinical hypothyroidism

Subclinical hypothyroidism can be diagnosed in 1% to 10% of the adult population, is more common in women, and increases with age. In many patients, treatment with L-thyroxine reduces low-density lipoprotein cholesterol, improves cardiac function, reduces symptoms of hypothyroidism, and diminishes neuropsychiatric symptoms. Treatment also reduces the likelihood of statin-induced myopathy. However, in double-blind, placebo-controlled trials of L-thyroxine therapy in subclinical hypothyroidism, cardiovascular and symptomatic benefits have been neither uniform nor definitive. In the absence of a large-scale, multicenter, randomized trial, physicians have to individualize therapy for each patient. Benefits of therapy are most likely to be realized in patients with thyroid-stimulating hormone levels greater than 10 mU/L on repeated measures, those with hypothyroid symptoms, those who are pregnant, those with a documented family history of hypothyroidism, and those with severe hyperlipidemia.

[Treatment of keloids and hypertrophic cicatrices]

BACKGROUND

Infertile women positive for thyroid antibodies suffer from a poor pregnancy/delivery outcome, although conflicting data have been published. Our objective was to investigate if levothyroxine (LT4) exerts any effect on pregnancy and/or delivery rates in thyroid peroxidase antibody (TPOAb)-positive (+) women undergoing assisted reproductive technologies.

METHODS

Patients undergoing treatment were screened for TPOAb, thyroid-stimulating hormone (TSH) and free thyroxine (FT4). A total of 72 (15%) out of the 484 euthyroid women selected were TPOAb (+). These 72 patients were randomly divided into two groups: group A (n = 36) underwent LT4 treatment, group B (n = 36) placebo. Group C consisted of 412 women (85%) who were TPOAb negative (-). All patients received controlled ovarian stimulation. The endpoints of treatment were pregnancy rate, miscarriage rate and delivery rate.

RESULTS

No differences in pregnancy rate were observed between the three groups. Miscarriage rate was higher in TPOAb (+) in comparison to TPOAb (-) [relative risk: 2.01 (95% CI = 1.13-3.56), P = 0.028].

CONCLUSIONS

The pregnancy rate is not affected either by presence of TPOAb or treatment with LT4. However, TPOAb (+) women show a poorer delivery rate compared to TPOAb (-). LT4 treatment in TPOAb (+) does not affect the delivery rate.