To determine the trajectories of platelet counts and the prevalence of gestational thrombocytopenia (<150 × 10/L) during normal pregnancies and pregnancies with complications, such as hypertensive disorders of pregnancy (HDP), preeclampsia, and fetal growth restriction (FGR).
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.
The trajectories of platelet counts and prevalence of gestational thrombocytopenia were evaluated in normal pregnant women, pregnant women with complications, and non-pregnant women.
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.
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.

Copyright © 2021 International Society for the Study of Hypertension in Pregnancy. Published by Elsevier B.V. All rights reserved.

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