Congenital hypothyroidism detected by neonatal screening: relationship between biochemical severity and early clinical features.

The relationships between biochemical severity of hypothyroidism (as judged by plasma thyroxine) and the clinical and radiographic findings at diagnosis were evaluated in 449 infants born in 1982-4 with congenital hypothyroidism identified by neonatal screening. Details of pregnancy, delivery, and the neonatal period were also examined and compared with the findings in a normal population of 36,727 infants born in 1988. Infants with plasma thyroxine values of 30 nmol/l or less had a significantly higher incidence of prolonged jaundice, feeding difficulties, lethargy, umbilical hernia and macroglossia, showed more severe delay of bone maturation on a knee radiograph, and had a higher proportion of thyroid agenesis on isotope scan. In contrast, an ectopic or hypoplastic gland was more common in infants with plasma thyroxine values above 30 nmol/l. Prevalence of illness in pregnancy and mode of delivery was not related to severity of hypothyroidism and were similar to figures for the normal population. Induction of labour, gestation over 40 weeks, and birth weight above 3500 g were significantly more common in the hypothyroid infants. Perinatal illness and congenital malformations were more common in the infants with low plasma thyroxine values at diagnosis.