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.