Congenital thyrotoxicosis in premature infants

OBJECTIVES Graves' disease (GD) complicates 0.1% to 0.2% of pregnancies, bu t congenital thyrotoxicosis is rare occurring in one in 70 of these pregnan cies independent of maternal disease status. Antenatal prediction of affect ed infants is imprecise; however, maternal history, coupled with a high mat ernal serum TSH receptor binding immunoglobulin index (TBII) predict advers e neonatal outcome. Mortality is reported to be as high as 25% in affected infants and would therefore be expected to be higher in premature infants. This study illustrates that in sick, premature, extreme low birth weight (E LBW) or intrauterine growth retarded (IUGR) infants, the diagnosis maybe ov erlooked especially in the absence of antenatal risk assessment and managem ent of thyrotoxicosis in this setting is complex. DESIGN and PATIENTS The records of premature neonates born at the three mai n maternity units in Brisbane, between January 1996 and July 1998 diagnosed with congenital thyrotoxicosis were reviewed. Data were recorded on gestat ional age, birth weight (B Wt), maternal thyroid history and current status , and neonatal course. Thyroid function and TBII status was assessed using standard biochemical assays. RESULTS Seven neonates from five pregnancies were identified (four female, three male). Mean gestational age was 30 week (25-36 week) and median B Wt was 1.96 kg (0.50-2.62 kg). Only one mother received formal antenatal couns elling by a paediatric endocrine service and had a TBII (54%) measured prio r to delivery. Three of five mothers had elevated TBII measured after diagn osis in their offspring (57%, 65%, 83%) and in one mother, a TBII was not p erformed. All mothers were biochemically euthyroid at delivery. Mean age at diagnosis was 9 days (1-16 days) and mean age at commencement of treatment was 12 days (7-26 days). Two infants received propylthiouracil and five re ceived a combination of carbimazole and propranolol. Pour became biochemica lly hypothyroid, in three this resolved with cessation of the antithyroid d rug (ATD), and one required ongoing T4 supplementation. Only one infant req uired treatment for cardiac failure and there were no deaths in this cohort . CONCLUSIONS This is a large series of extremely small and premature infants with neonatal thyrotoxicosis. Presentation was nonspecific. The diagnosis was delayed because of low birth weight, prematurity, multiple birth and/or an unrecognized maternal history of Graves' disease. The treatment of neon atal thyrotoxicosis was difficult in these extreme law birth weight infants yet no infant died and significant morbidity was confined to high output c ardiac failure in one infant. With antenatal recognition of past or active Graves' disease, assessment of maternal TSH receptor binding immunoglobulin index prior to delivery and postnatal monitoring of cord TSH and venous fT 4 and TSH on days 4 and 7 rapid treatment of affected infants may have furt her reduced neonatal morbidity.