Thyroxine derivatives in amniotic fluid. Fetal outcome in three patients with thyroid problems

Aplasia cutis congenita in surviving co-twin after propylthiouracil exposure in utero

AIM

Aplasia cutis congenita (ACC) has been observed after fetal exposure to the antithyroid drug methimazole (MMI), but not reported after propylthiouracil (PTU), the current antithyroid drug of choice during pregnancy. This occurrence has implications for patient information and causal research.

CASE REPORT

We describe a surviving term co-twin to a mother with hyperthyroidism exposed to PTU from conception to 34 weeks of gestation presenting with ACC at birth.

DISCUSSION

The association between PTU exposure and ACC is clinically relevant and allows speculation on the etiology. A similar mechanism to the classical MMI-induced ACC is postulated, unless a vascular etiology suggested by a vanishing twin or maternal hyperthyroidism itself is causal. Coincidence of PTU exposure and ACC seems unlikely.

CONCLUSION

ACC in a newborn after PTU exposure during pregnancy hitherto observed only after MMI strongly encourages further reports of similar cases that may remain clinically underdiagnosed or unreported. Such confirmation could have significant implications for maternal treatment of hyperthyroidism, common in women of childbearing age.

Fetal hydrops, associated with maternal propylthiouracil exposure, reversed by intrauterine therapy

Thyroid hormone is essential for fetal neurological development. Among other etiologies, fetal hypothyroidism may be caused by maternal exposure to antithyroid drugs (ATDs). The most common presentation of fetal hypothyroidism is fetal goiter, which can cause dystocia, in addition to airway obstruction in the neonate. Intra-amniotic treatment with levothyroxine normalizes fetal thyroid status and reduces goiter size. We present a case of fetal hypothyroidism diagnosed in a patient who was treated with propylthiouracil (PTU) for Grave's disease. The fetus had marked hydrops fetalis and a large goiter. In addition, anal stenosis, vesicovaginal fistula, bilateral pyelectasia and polydactyly were diagnosed in the neonate. Intra-amniotic treatment with levothyroxine resulted in a regression of the hydrops and a reduction in the goiter size. A euthyroid, non-edematous, non-goitrous neonate was delivered. At the age of 27 months the child's psychomotor development was normal. The present case indicates that hydrops fetalis may be an unusual manifestation of fetal hypothyroidism, caused by intrauterine exposure to maternal antithyroid drugs (ATDs), and that it may be resolved by treatment with intra-amniotic levothyroxine.

Amniotic fluid thyrotropin (TSH) following maternal administration of thyrotropin releasing hormone

Cord blood and amniotic fluid thyrotropin (TSH), T4, T3, and rT3 concentrations were measured in 49 women who received 400 micrograms thyrotropin releasing hormone (TRH) iv during labor and in 16 control women who received saline. Cord blood serum TSH concentrations were elevated for as long as 4 hours after TRH administration and peak values (38.0 +/- 4.2 microU/ml) were observed from 61-120 minutes after TSH as compared to control values of 5.0 +/- 0.3 microU/ml. The elevations in fetal TSH concentration stimulated the fetal thyroid, resulting in a progressive increase in cord blood T4 and T3 but not rT3 concentrations. These TRH induced elevations in fetal cord blood TSH concentrations were not accompanied by increases in unconcentrated and 4 fold concentrated amniotic fluid TSH concentrations which were almost always below 0.6 microU/ml, the limit of assay sensitivity. Unconcentrated amniotic fluid T4 concentrations were barely detectable and no variation was observed between the TRH treated and saline treated mothers; amniotic fluid T3 was not detectable in any of the groups; and amniotic fluid rT3 concentrations ranged between 46.4 and 55.6 ng/dl and did not differ between groups. These findings suggest that term amniotic fluid TSH values do not reflect transient but marked elevations in fetal serum TSH concentrations and that amniotic fluid TSH determination is probably not useful in the detection of primary fetal hypothyroidism. It is possible, but unlikely, that long-term and even greater elevations in fetal serum TSH concentrations would result in increased amniotic fluid TSH concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyroxine, 3,5,3' -triiodothyronine and 3,3', 5' -triiodothyronine in human amniotic fluid: relationships between concentrations and turnover

We have made estimates of the possible contributions of various routes of entry and disposal to the turnover of thyroxine (T4), 3,5,3'-triiodothyronine (T3) and 3,3',5'-triiodothyronine (reverse T3, rT3) in human amniotic fluid (AF). Our calculations suggest that, in normal pregnancy, AF T4 and T3 are derived mainly from the maternal circulation, and that their concentrations depend very largely on binding-protein concentrations. The majority of AF rT3 is unlikely to enter the amniotic sac directly from the maternal circulation, or from the fetal circulation by passive diffusion or fetal urinary excretion; however, our calculations are consistent with the hypothesis it is derived largely from inner-ring deiodination of T4 in the fetal membranes. We propose that the molar ratio of one AF iodothyronine to another may yield more information about fetal thyroid status than the total concentration of any single iodothyronine.

Graves' disease during pregnancy

Presented are two case studies which investigate the adverse effects of Graves' disease in pregnant women. Particular attention has been paid to the therapeutic regimen and its implications for the maternal, fetal and neonatal well-being. The first case study illustrates that Graves' disease complicating pregnancy can be treated by bed rest and careful observation of mother and fetus. The first pregnancy of our second case study confirms these results. Her second pregnancy, in which the symptoms of Graves' disease were far more severe, illustrates that it is possible to treat fetal hyperthyroidism by treating the pregnant mother with antithyroid drugs. If great care is taken to avoid overtreatment of the fetus, the treatment with antithyroid drugs is superior to surgical treatment, since surgery completely neglects the problem of fetal hyperthyroidism.

Radioimmunoassay of thyroxine and 3,3',5'-triiodothyronine (reverse T3) in human amniotic fluid

Measurement of amniotic fluid iodothyronine concentrations may enable antenatal detection of fetal thyroid abnormalities; however, the delineation of normal ranges is complicated by methodological problems associated with strong and highly variable protein-binding, and specificity of antisera. Improved radioimmunoassays of thyroxine (T4) and 3,3',5-triiodothyronine (reverse T3, rT3) have been developed to overcome these problems. In normal pregnancy, mean rT3 concentrations at less than 17 weeks, 17-22 weeks and 35-42 weeks gestation were 3.6 nmol/l (n = 21), 6.1 nmol/1 (n = 14) and 0.66 nmol/1 (n = 39) respectively; corresponding mean T4 concentrations were 2.4 nmol/1, 6.5 nmol/1 and 3.6 nmol/1. rT3 concentrations showed a strong positive correlation with T4 concentration in each age range; however, the molar ratio of rT3:T4 decreased progressively with gestational age, from 1.69 at less than 17 weeks to 0.19 at 35-42 weeks. In both mid- and late gestation, rT3 and T4 concentrations were strongly correlated with total amniotic fluid protein concentrations.

Hyperthyroidism complicating pregnancy: results of treatment by antithyroid drugs in 77 pregnancies

Seventy-seven pregnancies (79 infants) complicated by hyperthyroidism were seen at three Dublin Maternity Hospitals during a 25 year period. Hyperthyroidism was diagnosed following conception in 14 pregnancies. Treatment was with carbimazole alone in 73 pregnancies, in a usual dose of 5 to 10 mg daily. The total fetal loss was 15.2 per cent with a perinatal loss of 5.1 per cent. The perinatal loss in patients treated with carbimazole alone was 4.1 per cent (excluding one death due to congenital malformation). Four infants (5.1 per cent) had goitre and 57 (85.1 per cent) of the surviving infants were above the 25th centile for gestational age. Spontaneous premature labour occurred in 7 pregnancies (9.1 per cent). There was a relative excess of infants with a birth weight less than the 25th centile, of neonatal goitre and premature labour after pregnancy in which treatment was started following conception. Hyperthyroidism complicating pregnancy can be treated effectively with antithyroid drugs given alone and in the minimal effective dose.

Amniotic fluid thyroid hormone concentrations during human gestation

AFT4, AFT3, and AFrT3 concentrations were measured in samples from pregnant women between 10 and 43 weeks' gestation. During the first half of pregnancy, AFT4 and AFrT3 concentrations increased progressively, reaching peak levels at 25 to 30 and 17 to 20 weeks, respectively. AFT3 concentrations were low and increased slowly during this stage of pregnancy. During the last half of pregnancy, AFT4 and AFrT3 levels decreased while AFT3 continued to increase. This pattern of change is most likely explained by an increase in 5'-iodothyronine monodeiodinase activity in the fetal compartment. Normal values of amniotic fluid thyroid hormone concentrations as standards of reference for possible prenatal diagnosis of fetal thyroid abnormalities are provided.

Neonatal thyroid function in congenital hypothyroidism

In the cord blood of seven infants with congenital hypothyroidism detected in our newborn screening programs, thyroxine values ranged from 2.5 to 6.7 mug/dl and thyrotropin, from 105 to 975 muU/ml; triiodothyronine values were normal. On follow-up, T3 levels increased to normal in five infants, there was a significant negative correlation between the T3 value and the severity of thyroprevia as reflected in the TSH levels and the number of clinical features present. This increase in T3 may explain in part why the diagnosis of this disease is difficult during the first few months of life and why early treatment is effective. This observation provides further rationale for the widespread institution of newborn screening programs for congenital hypothyroidism.

Thyroid hormones and thyrotropin in amniotic fluid

Thyroid hormone and thyrotropin concentrations in amniotic fluid were studied by radioimmunoassays during pregnancy. The mean thyroxine concentration was 398 ng per 100 ml at 15 to 19 and 440 ng per 100 ml at 36 to 42 weeks. Although 3,3',5-tri-iodothyronine was undetectable (less than 25 ng per 100 ml), 3,3',5'-tri-iodothyronine levels were very high (range, 132 to 605 ng per 100 ml) at 15 to 30 weeks, but decreased substantially (range, 54 to 130 ng per 100 ml) thereafter. Thyrotropin was undetectable. The mean thyroxine and 3,3',5-tri-iodothyronine levels in amniotic fluid were much lower and the mean 3,3'5'-tri-iodothyronine much higher than the corresponding values in maternal serum at both 15 to 19 and 36 to 42 weeks of pregnancy. Measuring thyroid hormones in amniotic fluid, especially 3,3',5'-tri-iodothyronine, may aid in the diagnosis of fetal thyroid dysfunction and in identification of pregnancies of less than 30 weeks' gestation.

Thyroxine in human amniotic fluid

Total and free T3 and T4 concentrations were measured in human amniotic fluid and in fetal and maternal blood. Before 20 weeks, the mean AF-T4 level was 0.24 mug/dl; there is a progressive increase in concentration with gestational age. At term, the mean AF total T4 level was much less (0.64 mug/dl) than in fetal or maternal serum (9.3 and 11.3 mug/dl, respectively). Most of the T4 (99.4%) in AF is protein bound, presumably to TBG as in serum, but the mean FT4 concentration in AF at term (4.13 ng/dl) was significantly greater than the levels in fetal or maternal serum (2.67 or 2.56 ng/dl, respectively). The mean TBG level in AF at term was 0.26 mg/dl. T3 was not measurable in AF (less than 15 ng/dl). There were no significant correlations between the total or free T4 concentrations in maternal or fetal sera and in amniotic fluid. Thus AF thyroid hormone concentrations in the euthyroid fetus do not reliably reflect fetal serum T4 or T3 concentrations.