DECREASED PLATELET-AGGREGATION DURING PREGNANCY CORRELATES WITH GESTATIONAL-AGE

In vivo platelet aggregation was determined in pregnant women at diffe rent gestational ages and nonpregnant women by a modification of a met hod. A higher platelet count ratio (PCR) was found in pregnant women a fter a gestational age of 13 weeks. At 16-30 and 31-41 weeks of gestat ion, in vivo platelet aggregation was significantly decreased. The PCR , meaning the ratio of nonaggregated platelets to all circulating plat elets, correlated significantly with gestational age. It is suggested that the decrease in in vivo aggregation measured during pregnancy ref lects a summarized effect of different factors during pregnancy connec ted to placenta and uteroplacental vessels.