Congenital hypothyroidism with delayed TSH elevation in low-birth-weight infants: incidence, diagnosis and management

Objective: To evaluate the incidence of congenital hypothyroidism (CH) with delayed TSH elevation among low-birthweight (LBW) newborns in North-Eastern Italy and to verify if they need a second or third screening. Design: Analysis of clinical and biochemical data of newborns affected by CH with delayed TSH elevation identified by neonatal screening. Methods: Data of all newborns with birth weight (BW) <2500 g and evidence of delayed TSH elevation at newborn screening were collected between 2011 and 2014. Confirmatory tests were based on serum TSH and FT4 levels. All their clinical signs at diagnosis were reported. Results: 57.5% of LBW newborns with delayed TSH increase at neonatal screening presented a CH with delayed TSH elevation and began a treatment with l-thyroxine. The incidence of this condition in North-Eastern Italy is therefore 1:908. The remaining infants presented a subclinical hypothyroidism (21.25%) or a complete normal serum thyroid function (21.25%). These data could be drawn only from a retesting strategy of neonatal screening. Conclusions: Our report describes the incidence of CH with delayed TSH rise in North-Eastern Italy and differentiates this clinical condition from other thyroid dysfunctions of preterm or LBW newborns. The second-screening strategy for CH in neonates with BW < 2500 g proved useful in detecting newborns who otherwise would not be identified at the first screening.