Fetal sex and variations in kinetic properties of neutrophil alkaline phosphatase during the second trimester of normal pregnancy.

A kinetic parameter (the Vm/Km ratio), an index of neutrophil alkaline phosphatase catalytic efficiency, was studied in 36 women with normal pregnancies at 16-20 weeks' gestation. On each blood sample, determinations were achieved on enzyme extracted from maternal granulocytes by monitoring the phosphohydrolytic activity at 400 nm on a spectrophotometer equipped with software for computation of kinetic parameters. Infant sex was recorded at the delivery for all women included in this study. The recent introduction of NAP as a marker for some pathological pregnancies requires a better knowledge of the behaviour of that enzyme in physiological conditions. Data reported focus attention on fetal sex. It appears to be one of the factors involved in variations of kinetic parameters observed in maternal NAP. Sex-linked differences in placental maturation could explain these results.