Increased platelet-activating factor-acetylhydrolase activity in the umbilical venous plasma of growth-restricted fetuses

Objective: To determine whether platelet-activating factor-acetylhydrolase activity in fetal plasma obtained at birth from umbilical vessels is different from that in maternal plasma, and (2) to compare platelet-activating factor-acetylhydrolase activity in cord plasma from fetuses with fetal growth restriction (FGR) and those with appropriate growth for gestational age (AGA). Methods: Platelet-activating factor-acetylhydrolase activity was measured in the plasma of 22 nonpregnant healthy women, 16 pregnant women at term during labor, 28 fetuses exhibiting AGA, and seven fetuses with FGR. Results: Plasma platelet-activating factor-acetylhydrolase activity in normotensive pregnant women at 37-41 weeks' gestation was 28.1 +/- 16.6 nmol/mL per minute, which was not statistically different from the activity in nonpregnant women (30.8 +/- 11.1 nmol/mL per minute). Platelet-activating factor-acetylhydrolase activity in venous cord plasma from AGA fetuses was significantly (P < .01) lower than that in maternal plasma (6.3 +/- 2.6 nmol/mL per minute), and there was no difference between the activities found in arterial and venous cord samples. In FGR fetuses, venous cord platelet-activating factor-acetylhydrolase activity was significantly (P < .01) higher (12.1 +/- 1.4 nmol/mL per minute), than the activity seen in AGA fetuses, and when the data from AGA and FGR fetuses were considered together, there was a negative correlation between cord plasma platelet-activating factor-acetylhydrolase activity and neonatal body weight (r = .46, P = .006). Conclusion: Platelet-activating factor hydrolysis is significantly lower in fetuses than adults. Further, the comparatively high platelet-activating factor-acetylhydrolase activity in FGR fetuses suggests the existence of a compensatory mechanism to maintain microcirculation within the placenta. (Obstet Gynecol 1999;93:180-3. (C) 1999 by The American College of Obstetricians and Gynecologists.).