Platelet counts during normal pregnancies and pregnancies complicated with hypertensive disorders

Objectives: To determine the trajectories of platelet counts and the prevalence of gestational thrombocytopenia (<150 × 10⁹/L) during normal pregnancies and pregnancies with complications, such as hypertensive disorders of pregnancy (HDP), preeclampsia, and fetal growth restriction (FGR). Study design: A multicenter retrospective study was conducted using laboratory data on women who delivered term singletons at 11 primary maternity care units between 2011 and 2018 (n = 35,045), and non-pregnant women who underwent a medical check-up between 2016 and 2019 (n = 61,189). After 1:1 matching, 28,073 pregnant women and 28,073 non-pregnant women were selected for analysis. Main outcomes measures: The trajectories of platelet counts and prevalence of gestational thrombocytopenia were evaluated in normal pregnant women, pregnant women with complications, and non-pregnant women. Results: The platelet counts declined throughout pregnancy, with the nadir occurring on postpartum day 1. The platelet counts recovered to the level of the non-pregnant state at postpartum 2–7 days. The mean platelet counts at postpartum day 1 decreased by an estimated 19.8% and 9.7% compared to those in the non-pregnant state and first trimester, respectively. The prevalence of gestational thrombocytopenia in normal pregnant women at 37–41 gestational weeks and in pregnant women with complications of HDP, preeclampsia, and FGR were 6.1%, 7.3%, 17.5%, and 7.7%, respectively. Conclusion: Platelet counts declined throughout pregnancy and recovered to the level of the non-pregnant state in the early postpartum period. Gestational thrombocytopenia is common during normal pregnancy, and its prevalence is significantly higher in women with preeclampsia.