Permanent and transient congenital hypothyroidism in preterm infants

Transient fluctuations in thyroid function are well recognized in preterm infants. We wanted to assess TSH variation in babies with transient and permanent congenital hypothyroidism (CHT).

Whole bloodspot TSH data in preterm infants (<35 weeks; 2005-2010) were assessed, and infants with bloodspot TSH values >6 mU/L identified. Permanent CHT was defined as a requirement for thyroxine beyond 3 years of age.

A first TSH sample was obtained from 5518 infants (median gestational age, 32 w; range, 22-35), with a second sample obtained from 5134 infants (median gestational age, 32 w; range, 22-35). Five infants had raised TSH concentrations on both occasions. Three of the five infants had a serum TSH >80 mU/L on second screen but two came off thyroxine beyond 3 years of age. All preterm babies with permanent or transient hypothyroidism were detected by the first TSH cut-off of 6 mU/L. Only one infant with a birth weight <1500 g remains on thyroxine treatment beyond 2 years of age.

The incidence of permanent CHT in preterm infants is similar to term infants. Profound abnormalities of thyroid function can occur in preterm babies with transient hypothyroidism but both categories of hypothyroidism can be detected by a 'once-only' TSH screening strategy with a relatively low cut-off.