NONINVASIVE MEASUREMENT OF PLATELET KINETICS IN NORMAL AND HYPERTENSIVE PREGNANCIES

OBJECTIVE: Our purpose was to determine platelet kinetics in pregnancy by means of noninvasive reticulated platelet counts and to examine in a pilot study whether increased reticulated platelet values were asso ciated with preeclampsia and pregnancy-induced hypertension. STUDY DES IGN: Nulliparous women had blood samples drawn at enrollment (first pr enatal visit) and at 28 and 36 weeks' gestation. The percent of reticu lated platelets (an index of marrow platelet release correlating with increased thrombopoiesis), platelet-associated immunoglobulin, and ser um antiplatelet antibody were measured and correlated with the clinica l course for each patient. RESULTS: In 31 normal pregnancies the perce nt of reticulated platelets was never significantly higher than the va lues for normal nonpregnant women (5.8% +/- 2.2%) in spite of a signif icant decrease in platelet count by 36 weeks. By contrast, the percent of reticulated platelets in four women with preeclampsia rose signifi cantly to 13.9% +/- 11.2% at 28 weeks, before the onset of clinical si gns. No women had evidence of immune platelet destruction. CONCLUSION: In normal pregnancy the decline in platelet count is not accompanied by an increase in marrow platelet production, suggesting that the plat elet decrease is dilutional without a compensatory thrombopoietic resp onse or alternatively that thrombopoiesis is down-regulated during nor mal pregnancy. However, platelet production does increase before the o nset of symptoms in a small number of women in whom preeclampsia or pr egnancy-induced hypertension subsequently develops. These findings may justify a larger prospective study to determine whether noninvasive s erial measurement of the percent of reticulated platelets can predict those pregnant women at risk for hypertension and preeclampsia.