Review of primary hypothyroidism in very low birthweight infants in a perinatal centre in Hong Kong.

AIMS: To review the incidence and risk factors of primary hypothyroidism in very low birthweight (VLBW) infants in our centre and to assess their neurodevelopmental outcome.

METHOD: Retrospective, descriptive review of VLBW infants with primary hypothyroidism from 1 January 2000 to 31 December 2008 in a perinatal centre. Case control comparisons for neurodevelopmental outcome at 18 months, nested to a prospective VLBW cohort (Vermont Oxford Database).

RESULTS

Twelve cases were identified, with the incidence of primary hypothyroidism of 1 in 55 live births in our VLBW cohort during the 9-year study period. Umbilical cord blood thyroid-stimulating hormone was abnormal in less than half of the cases using the current cut-off (≤14 mIU/L). Five cases were transient in nature, four cases were permanent and the causes for the rest remained undetermined at the time of review. Elevation of thyroid-stimulating hormone was first evident at a mean of 2.4 weeks post-natally. Follow-up assessment reviewed normal development in 83% of cases (10 out of 12 cases). There was no statistically significant difference in Griffith's scores at 18 months between the case and matched controls.

CONCLUSIONS

The high incidence of primary hypothyroidism in our VLBW cohort deserved stringent monitoring of thyroid function post-natally. Umbilical cord blood screening was not useful as a screening tool because of its low sensitivity. Neurodevelopmental outcome for treated primary hypothyroidism was favourable as assessed at 18 months of age.