The natural history of thrombocytopenia associated with preeclampsia. Sixty-one of 375 women with hypertension and preeclampsia in a 48-month period had thrombocytopenia. By postpartum day 3, 90% of these women had rising platelet counts, and by day 4, 59 of 61 women had counts greater than 100,000/mm3. The two exceptions had other pathologic conditions in addition to preeclampsia. Thrombocytopenia associated with preeclampsia should resolve by postpartum day 4. 