Maternal serum alpha-fetoprotein in normal pregnancy.

Serial measurements of alpha-fetoprotein (AFP) were made in 63 normal pregnancies throughout gestation using a radioimmunoassay. Significant levels of AFP, which were detected as early as at 10 weeks gestation, showed a gradual rise until 32 weeks, after which the levels declined until term. The limits of the normal gestational pattern have been defined and the intrapatient variability of the assay was examined. A comparison of the clinical characteristics of the pregnancies with levels of AFP was made. Higher birth weights were correlated with later attainment of peak levels of AFP and peak levels were achieved earlier in gestation in female fetuses. Higher levels of AFP and lower oestriol/AFP ratios were correlated with an earlier onset of labour.