Maternal serum heat-stable alkaline phosphatase. In normal and high-risk pregnancies.

To evaluate its specificity as an indicator of placental function or fetal status, maternal serum heat-stable alkaline phosphatase (HSAP) was measured serially in 76 normal and 161 high-risk pregnancies (1272 determinations). The previously reported curvilinear HSAP rise starting at about 28 gestational weeks was noted. No relation was seen between HSAP levels and milk or moderate hypertension, gestational diabetes, nontoxemic placental insufficiency, or maternal blood group. HSAP levels were mostly above normal in proteinuric hypertension and were low normal in pregnant insulin-dependent diabetics. Two neonatal deaths were associated with normal HSAP levels. Of 4 intrauterine deaths, 1 was associated with high, 1 with low, and 2 with rising values in the normal range. Serial maternal HSAP values are apparently not a specific indicator of placental function or fetal status.