Prevalence:

• 1 in 5,000 births.

Ultrasound diagnosis:

• Anterior cervical echogenic mass of variable size. The fetal head may be hyperextended and polyhydramnios is common due to mechanical obstruction of the esophagus.
• Most cases of fetal thyroid goitre are the consequence of fetal hypothyroidism due to transplacentally derived anti-thyroid drugs used for the treatment of maternal hyperthyroidism. A less common cause of hypothyroid goitre is congenital dyshormonogenesis due to defects in genes involved in the pathway of thyroid hormone production. In hypothyroidism the fetus may have impaired growth and bradycardia.
• Hyperthyroid goitre is rare and it is caused by transplacentally derived maternal thyroid stimulating immunoglobulins in recently diagnosed Graves’ disease. The fetus may have impaired growth, tachycardia, heart failure and decreased movements.

Associated abnormalities:

• The incidence of chromosomal abnormalities and genetic syndromes is not increased.

Investigations:

• Detailed ultrasound examination.
• In most cases assessment of the maternal condition can help decide whether the cause is fetal hypothyroidism or hyperthyroidism. In uncertain cases, cordocentesis and measurement of fetal blood thyroid hormones and TSH can help distinguish between hypothyroidism, with low thyroid hormones and high TSH, due to antithyroid drugs or congenital dyshormonogenesis, and hyperthyroidism, with high thyroid hormones and low TSH, due to thyroid stimulating immunoglobulins

Therapy:

• Fetal hyporthyroid goitre: reduce or even discontinue maternal antithyroid medication aiming to maintain maternal blood thyroxine levels in the upper level of the normal range. The second-line of treatment is intra-amniotic injection of levothyroxine (100 μg / kg) every 1-2 weeks until delivery at term. The goitre usually decreases in size within a few days after the first course of treatment. Subsequent injections are given depending on sonographic evidence of re-enlargement of the gland or serial measurements of levels of thyroid hormones in amniotic fluid or fetal blood.
• Fetal hyperthyroid goitre: administration of antithyroid drugs to the mother. The fetal goitre usually decreases in size within a few days, but if this does not occur measurement of levels of thyroid hormones in fetal blood may be needed and the dose of antithyroid drugs given to the mother adjusted as necessary.

Follow-up:

• Every 4 weeks to monitor fetal growth, size of the tumor, fetal heart rate, amniotic fluid volume and cervical length.

Delivery:

• Place: hospital with neonatal intensive care and pediatric surgery.
• Time: 38 weeks.
• Method: cesarean section and EXIT if there is hyperextension of the neck and polyhydramnios

Prognosis:

• Good.
•  Untreated congenital hypothyroidism is associated with neurodevelopmental delay.

Recurrence:

• Thyroid dyshormonogenesis is autosomal recessive: 25%.
• The rest of cases: no increased risk of recurrence.