Plasma pressor activity (PPA) was measured in umbilical plasma of 29 full-term newborn infants and two sets of twins using a modified in vitro bioassay which reflects primarily plasma levels of epinephrine and norepinephrine. Full-term newborn infants with asphyxia neonatorum demonstrated significant hypercapnia, acidemia, lower Apgar scores, and elevated PPA as compared to normal.

Eight newborn infants born to mothers with mild preeclampsia as well as the second born of twins showed similar trends. Pooled data on all newborn infants revealed a highly significant correlation between umbilical artery PPA and Paco2, pHa, as well as Apgar scores at 1 and 5 minutes.

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