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 associated with preeclampsia and pregnancy-induced hypertension.

Study Design: Nulliparous women had blood samples drawn at enrollment (first prenatal visit) and at 28 and 36 weeks' gestation. The percent of reticulated platelets (an index of marrow platelet release correlating with increased thrombopoiesis), platelet-associated immunoglobulin, and serum antiplatelet antibody were measured and correlated with the clinical course for each patient.

Results: In 31 normal pregnancies the percent of reticulated platelets was never significantly higher than the values for normal nonpregnant women (5.8% +/- 2.2%) in spite of a significant decrease in platelet count by 36 weeks. By contrast, the percent of reticulated platelets in four women with preeclampsia rose significantly to 13.9% +/- 11.2% at 28 weeks, before the onset of clinical signs. 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 platelet decrease is dilutional without a compensatory thrombopoietic response or alternatively that thrombopoiesis is down-regulated during normal pregnancy. However, platelet production does increase before the onset of symptoms in a small number of women in whom preeclampsia or pregnancy-induced hypertension subsequently develops. These findings may justify a larger prospective study to determine whether noninvasive serial measurement of the percent of reticulated platelets can predict those pregnant women at risk for hypertension and preeclampsia.