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Leukocyte alkaline phosphatase (LAP) activity was studied in 50 women at delivery and in the newborn after delivery. The following findings were observed: (1) the LAP activity of newborns is lower than that of the mothers; (2) significant decrease in the LAP activity has been observed in newborns on the 4th day after delivery; (3) there are no significant differences between newborns from normal and prolonged labor; (4) immediately after delivery the LAP scores of male newborns are lower than those of females, but 4 days later these scores were reversed, and (5) 4 days after delivery, the LAP scores do correlate to the weight of the newborn.

Leukocyte alkaline phosphatase (LAP) activity increases progressively during pregnancy, returning to non-pregnant levels 6 weeks post-partum. This enzymatic activity is under the influence of placental steroid hormones, thus reflecting placental function. LAP activity is thus a reflection of the dynamic relations between estrogenic, progestational and corticoid activity during pregnancy. LAP activity was studied in 60 women and in their 61 newborn infants at delivery and during the first five days of the puerperium. The Kaplow cytochemical technique was employed. The average maternal LAP score as well as the average newborn infant LAP score was considerably higher than the LAP score of the normal adult. The level of the enzyme in the maternal granulocytes was significantly higher than that of the newborn (Tab. I). During the first five days after labor, there was progressive decrease in the LAP score in the maternal and the newborn blood; on the fifth day the LAP scores of both were only slightly above the normal adult score (Figs. 1, 2). An inverse relation between the LAP score and the birth weight of the infant was found (Tab. III). These results confirm the view that LAP activity in the fetus in utero, are dependent on placental steroid function. The lower LAP values in the newborn, as compared to those of the mother are probably dependent on the lower newborn hormone levels. The significance of the relation between LAP scores and the infants birth weight is not clear.