Origins and significance of the increased plasma alkaline phosphatase during normal pregnancy and pre-eclampsia.

Total alkaline phosphatase (AP) was measured in maternal plasma, cord plasma and placental extracts in normal and in pre-eclamptic pregnancies. Total plasma AP was significantly elevated during the last two trimesters in normal and pre-eclamptic pregnancies, but contrary to previous reports, both placental and bone AP isoenzymes contributed to the significant elevation of total AP in both types of pregnancy. There was no placental AP isoenzyme in cord plasma but total cord plasma AP was higher in normotensive pregnancies than in pre-eclamptic pregnancies. Total AP concentration in placental tissue was higher in normotensive pregnancies than in pre-eclamptic pregnancies. A correlation was established between placental weights and maternal circulating placental AP.