Diagnosis and management of maternal and fetal thyroid disorders

Medications in pregnancy and lactation: part 1. Teratology

One of the least-developed areas of clinical pharmacology and drug research is the use of medication during pregnancy and lactation. This article is the first in a two-part series designed to familiarize physicians with many aspects of the drugs they commonly prescribe for pregnant and breast-feeding women. Almost every pregnant woman is exposed to some type of medication during pregnancy. Although the majority of pregnant and breast-feeding women consume clinically indicated or over-the-counter drug preparation regularly, only few medications have specifically been tested for safety and efficacy during pregnancy. There is scant information on the effect of common pregnancy complications on drug clearance and efficacy. Often, the safety of a drug for mothers, their fetuses, and nursing infants cannot be determined until it has been widely used. Absent this crucial information, many women are either refused medically important agents or experience potentially harmful delays in receiving drug treatment. Conversely, many drugs deemed "safe" are prescribed despite evidence of possible teratogenicity. Novel research and diagnostic applications evolving from the opportunities presented by the advances in genomics and proteomics are now beginning to affect clinical diagnosis, vaccine development, drug discovery, and unique therapies in a modern diagnostic-therapeutic framework-part of the new scientific field of theranostics. This review critically explores a number of recently raised issues in regard to the use of several classes of medications during gestation and seeks to provide a general and concise resource on drugs commonly used during pregnancy and lactation. It also seeks to make clinicians more aware of the controversies surrounding some drugs in an effort to encourage safer prescribing practices through consultation with a maternal-fetal medicine specialist and through references and Web sites that list up-to-date information.

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

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

Collision of Basic and Applied Approaches to Risk Assessment of Thyroid Toxicants

Thyroid hormone (TH) is essential for normal brain development; therefore, any environmental chemical that interferes sufficiently with thyroid function, TH metabolism, or TH action may exert adverse effects on brain development. Important known differences in aspects of thyroid endocrinology between the fetus, infant, and adult allow us to identify age-dependent vulnerabilities to thyroid toxicants with some confidence. These differences include the size of the hormone pool stored in the thyroid gland at different ages as well as the age-dependent sensitivity to mild TH insufficiency. Several recent studies that describe risk assessments of the environmental contaminant, ammonium perchlorate, provide good examples of conclusions based on the selective consideration of these known aspects of the thyroid system. Specifically, authors who consider age-dependent differences in thyroid endocrinology suggest that safe levels of perchlorate should be set at relatively low levels (low parts per billion). In contrast, authors who do not consider these known age-dependent differences in thyroid endocrinology recommend safe levels of perchlorate at high (hundreds) parts per billion to parts per million. Emerging evidence indicates that a variety of high production volume chemicals can directly interact with the TH receptor. As testing paradigms are designed by regulatory agencies, these age-dependent differences in thyroid endocrinology must be considered.

Intrauterine diagnosis and management of fetal goitrous hypothyroidism: a report of an Iranian family with three consecutive pregnancies complicated by fetal goiter

The diagnosis and treatment of hypothyroidism during the fetal period may decrease perinatal morbidity and are believed to be important to optimize growth and intellectual development. Herewith a case report of fetal goitrous hypothyroidism is presented in a euthyroid mother, detected at 34 weeks' gestation by ultrasonography, and treated with intra-amniotic levothyroxine injections. The mother had two previous consecutive pregnancies (13 and 8 years ago), also complicated by the occurrence of fetal goiter, resulting in tracheal compression, asphyxia, and early neonatal death in the first and in an emergency cesarean section delivery, because of fetal malpresentation, in the second neonate affected by congenital hypothyroidism (CH). The present male newborn, although born without observable goiter, had a large thyroid on ultrasonography and an early rise of his peripheral venous blood thyrotropin confirmed the diagnosis of CH. Low serum thyroglobulin in the proband and his older brother and parental consanguinity was mostly compatible with a thyroglobulin defective synthesis and secretion as the cause of CH and fetal goiter. Despite apparently sufficient dose of intraamniotic levothyroxine injections repeated weekly from 34-37 weeks' gestation (i.e., four injections of 500 microg levothyroxine), neonatal bone age on the second day of life showed delayed skeletal maturation.

Central congenital hypothyroidism due to gestational hyperthyroidism: detection where prevention failed

Much worldwide attention is given to the adverse effects of maternal Graves' disease on the fetal and neonatal thyroid and its function. However, reports concerning the adverse effects of maternal Graves' disease on the pituitary function, illustrated by the development of central congenital hypothyroidism (CCH) in the offspring of these mothers, are scarce. We studied thyroid hormone determinants of 18 children with CCH born to mothers with Graves' disease. Nine mothers were diagnosed after pregnancy, the majority after their children were detected with CCH by neonatal screening. Four mothers were diagnosed during pregnancy and treated with antithyroid drugs since diagnosis. Another four mothers were diagnosed before pregnancy, but they used antithyroid drugs irregularly; free T(4) concentrations less than 1.7 ng/dl (<22 pmol/liter) were not encountered during pregnancy. All neonates had decreased plasma free T(4) concentrations (range 0.3-0.9 ng/dl, 3.9-11.5 pmol/liter); plasma TSH ranged between 0.1 and 6.6 mU/liter. TRH tests showed pituitary dysfunction. Seventeen children needed T(4) supplementation. Because all mothers were insufficiently treated during pregnancy, it is hypothesized that a hyperthyroid fetal environment impaired maturation of the fetal hypothalamic-pituitary-thyroid system. The frequent occurrence of this type of CCH (estimated incidence 1:35000) warrants early detection and treatment to minimize the risk of cerebral damage. A T(4)-based screening program appears useful in detecting this type of CCH. However, the preferential and presumably best strategy to prevent CCH caused by maternal Graves' disease is preserving euthyroidism throughout pregnancy.

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

OBJECTIVE

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

DESIGN

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

MEASUREMENTS

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

RESULTS

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

CONCLUSIONS

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

Prenatal diagnosis and early in utero management of fetal dyshormonogenetic goiter

We present a case of a fetal dyshormonogenetic goiter diagnosed by ultrasound examination at 24 weeks of gestation, in a woman with no past history of thyroid disease or goitrogen treatment and with normal thyroid tests, including absence of auto-antibodies. In this situation, fetal goiter may only be associated with fetal hypothyroidism, therefore cord blood sampling was not performed but early treatment was initiated. Amniotic fluid instillation of thyroid hormone led to a rapid decrease in amniotic fluid volume and a clear reduction in thyroid goiter. However, fetal thyroid volume did not totally normalise, and cord blood analysis at birth showed elevated fetal TSH level. As prenatal treatment of fetal hypothyroidism remains controversial in euthyroid mothers, the main objective is to prevent obstetrical complications of large goiters. Therefore, in some selected cases with no maternal history of thyroid disease and normal thyroid function tests, cordocentesis is not necessary to confirm fetal thyroid status or to adjust fetal treatment.