Hypothyroidism, fetal

Myxedema and goiter are the main conditions for which thyroid preparations are indicated. The treatment of cretinism is difficult because it is recognized only at or after birth. Even if this disease could be diagnosed m utero, thyroid hormones do not readily cross the placental barrier. In addition, the fetus, as does a premature infant, rapidly deactivates the thyroid hormones. The halogen-free analogue DlMlT [26384-44-7] (3), which is resistant to fetal deiodinases, may prove useful for fetal hypothyroidism (cretinism). 

MMI and PTU can lead to methimazole embryopathy with choanal or esophageal atresia. In pregnant women the antithyroid diug dose should be minimized to prevent fetal hypothyroidism by maintaining the maternal free thyroxine serum level slightly above the upper limit of normal. 

Hypothyroid women frequently have anovulatory cycles and are therefore relatively infertile until restoration of the euthyroid state. This has led to the widespread use of thyroid hormone for infertility, although there is no evidence for its usefulness in infertile euthyroid patients. In a pregnant hypothyroid patient receiving thyroxine, it is extremely important that the daily dose of thyroxine be adequate because early development of the fetal brain depends on maternal thyroxine. In many hypothyroid patients, an increase in the thyroxine dose (about 30-50%) is required to normalize the serum TSH level during pregnancy. Because of the elevated maternal TBG levels and, therefore, elevated total T4 levels, adequate maternal thyroxine dosages warrant maintenance of TSH between 0.5 and 3.0 mll/L and the total T4 at or above the upper range of normal. 

Weber G, Vigone MC, Rapa A, Bona G, Chiumello G. Neonatal transient hypothyroidism aetiological study. Italian Collaborative Study on Transient Hypothyroidism. Arch Dis Child Fetal Neonatal Ed 1998 79(l) F70-2. 

I is given during pregnancy, fetal hypothyroidism and chromosomal aberrations can occur (33). 

Both the thiouracils and thioimidazoles readily cross the placenta and can cause fetal hypothyroidism, resulting in a slight delay in neurological or bone maturation. Various degrees of goiter have also been observed, even to the extent of severe tracheal compression and death. Antithyroid drug dosage should therefore be reduced to the minimum required to maintain a euthyroid state without supplementation of levothyroxine (93). 

De Catte L, De Wolf D, Smitz J, Bougatef A, De Schepper J, Foulon W. Fetal hypothyroidism as a complication of amiodarone treatment for persistent fetal supraventricular tachycardia. Prenat Diagn 1994 14(8) 762-5. 

Vanbesien J, Casteels A, Bougatef A, De Catte L, Foulon W, De Bock S, Smitz J, De Schepper J. Transient fetal hypothyroidism due to direct fetal administration of amiodarone for drug resistant fetal tachycardia. Am J Perinatol 2001 18(2) 113-6. 

Fetal problems, including abortion, stillbirths, congenital anomalies, neurological cretinism. Goiter, hypothyroidism, impaired mental function, increased susceptibility to radiation. 

Ultrasound has superseded amniofetography, a procedure in which contrast media are injected into the amniotic sac during pregnancy to delineate fetal abnormalities. Diatrizoate, iotalamate, and, earher, iodized oil were used. There is a theoretical risk of premature labor. Accidental injection of contrast medium into the fetal subcutaneous tissues could cause sloughing of the skin or subcutaneous necrosis. Cases of thyroid hjrperplasia or hypothyroidism were also commonly described. 

Maria B, Denavit MF, Leger A, Barrat J, Sureau C. Hypothyroidie foetale une complication de I amniofoeto-graphie. A propos de 3 observations. [Fetal hypothyroidism a complication of amniofetography. Apropos of 3 cases.] J Gynecol Obstet Biol Reprod (Paris) 1977 6 (7) 951-62. 

Oide S, Yamaguchi H, Niizu N, Takahashi S, Takashima K. [Transient neonatal hypothyroidism probably due to contrast media used in fetal radiography.] Horumon To Rinsho 1983 31(Suppl) 76-9. 

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