A rare case of dyshormonogenetic fetal goiter responding to intra-amniotic thyroxine injections

Fetal goiter was detected by routine ultrasound in early pregnancy, gestational week (GW) 18, in a 28-year-old woman with no thyroid history, normal thyroid hormone levels and no TSH receptor or thyroid peroxidase antibodies. An umbilical cord blood sample was drawn in GW 23. The analysis indicated fetal hypothyroidism with TSH >100 mU/l (reference value 6.8 ± 2.9, mean ± SD), fT4 3.8 pmol/l (reference value 16.5 ± 5.3, mean ± SD). Intra-amniotic injections of thyroxine were given in conjunction with ultrasound every 7-10 days, in total nine times during GW 24-33. A dose of 10 µg thyroxine/kg of estimated fetal weight per day was administered on six occasions, and 5 µg/kg/day the last three times. Upon injections of thyroxine further growth of the goiter was reduced. Elevated amniotic TSH levels fell from 13 to 2.5 mU/l (reference range 0.04-0.51). Throughout pregnancy, fetal heart rate and skeletal maturation were within normal limits. In week 34, chorioamnionitis was suspected and the child was delivered by cesarean section. Cord blood revealed TSH 596 mU/l (reference value 8.0 ± 5.12, mean ± SD), fT4 4.4 pmol/l (reference value 19.3 ± 4.3, mean ± SD) and total T3 1.18 nmol/l (reference value 0.5 ± 0.3, mean ± SD); the newborn was put on thyroxine supplementation. Psychomotor development of the child, now 3 years old, has been uneventful. The reported experience of treating dyshormonogenetic fetal goiter is limited but growing, creating a need for guidelines on administration of intra-amniotic thyroxine and monitoring treatment.