Serum alpha-fetoprotein--a biochemical indicator of prenatal hypothyroidism.

Serum alpha-fetoprotein (AFP) was analysed at 10-30 days of age in infants with positive TSH screening tests for congenital hypothyroidism. These levels were significantly higher in infants with true positive screening tests than in those with false positive tests; 27 of 43 infants with congenital hypothyroidism had serum AFP levels above the age-related reference range. The postnatal rate of elimination of AFP from serum did not differ in hypothyroid and euthyroid infants, indicating that the difference in serum AFP was due to more extensive synthesis in hypothyroid individuals. The level of serum AFP was inversely correlated with the roentgenological skeletal maturation index. It is postulated that increased serum AFP is caused by prenatal hypothyroidism and that analysis of serum AFP is a valuable tool to identify those infants with congenital hypothyroidism who are at risk of neuropsychological sequelae.