FETAL GOITER (9-15)

Antenatal diagnosis is essential as timely recognition and treatment is essential to achieve normal growth and neurological development. Untreated fetal hypothyroidism may result in mental retardation, language, motor and spatial problems, growth retardation, congenital heart block and delayed skeletal maturation.

A large fetal thyroid gland may also result in fetal malposition due to hyperextension of the neck, tracheal obstruction, esophageal compression and polyhydramnios, neonatal asphyxia and death.

RISK FACTORS FOR FETAL GOITER

Risk factors for fetal goiter (goiter in the fetus may be due to either hypothyroidism or hyperthyroidism):

1. Previous medical therapy for hyperthyroidism.

2. Previous high dose irradiation of the neck.

3. Thyroid autoimmune disease (thyroiditis).

4. Family history of thyroid disease.

5. Treatment with amiodarone.

6. Type I maternal diabetes mellitus.

7. Hypopituitarism.

FETAL HYPOTHYROIDISM

Transient fetal hypothyroidism is most frequently associated with maternal ingestion of anti-thyroid drugs (propylthiouracil –PTU; carbimazol; I-131 in pregnant women).

FETAL HYPERTHYROIDISM

Fetal Hyperthyroidism is usually secondary to maternal autoimmune disease. In Graves disease the mother produces several IgG thyroid stimulating immunoglobulins which can cross the placenta and cause fetal hyperthyroidism. Fetal tachycardia is usually the first sign of fetal hyperthyroidism, usually arising after the 25^th week of gestation. Sustained fetal tachycardia can result in high output cardiac failure.

ULTRASOUND

• Scans of the fetal neck may demonstrate thyroid size, and to detect dorsiflexion of the fetal neck if a goiter is present.
• There may be generalized thyroid enlargement or less commonly thyroid cysts.
• Doppler has been used to evaluate regression of fetal goiter after medical treatment.
• Fetal tachycardia (>160 bpm after 28 weeks).
• IUGR.

REFERENCES

1. Suchet I Ultrasound of the Fetal Neck in the second and third trimester. Part 3. Anomalies of the anterior and anterolateral nuchal region Can Assoc Radiol J 1995; 46:426-433
2. Hadi HA, Strickland D. In utero treatment of fetal goitrous hypothyroidism caused by maternal Graves disease. Am J Perinataol 1995;12(6):455-458.
3. Van Loon AJ, Derksen JT, Bos AF et.al. In utero diagnosis and treatment of fetal goitrous hypothyroidism, caused by maternal use of prpoylthiouracil. Prenat Diagn 1995;15:599-604.
4. Bruner JP, Dellinger EH. Antenatal diagnosis and treatment of fetal hypothyroidism. Fetal diagn Ther 1997;12:200-204.
5. De Catte L, de Wolf De, Smitz J et.al. Fetal hypothyroidism as a complication of amiodarone treatment for persistent supraventricular tachycardia. Prenat Diagn 1994;14:00-04/
6. Bromley B, Frigoletto FD, Cramer D et.al. The fetal thyroid: normal and abnormal measurements. J Ultrasound Med 1992;11:25-28.
7. Fisher DA. Fetal thyroid function: diagnosis and management of fetal thyroid disorders. Clin Obstet Gynecol 1997;40:16-31.
8. Nicoli U, Venegoni E, Acaia B et.al. Prenatal treatment of fetal hypothyroidism: is there more than one option? Prenat Diagn 1996;16:443-448.