Association Between Mild Thrombocytopenia Prior to Cesarean Section and Postpartum Hemorrhage

<b>Objective:</b> In this study, we aimed to evaluate the impact of mild thrombocytopenia on the incidence of postpartum hemorrhage (PPH) and associated clinical outcomes in a cohort of pregnant women who delivered via cesarean section. <b>Methods:</b> Women who underwent cesarean delivery at two tertiary medical centers in Korea between January 2009 and December 2019 were included in this retrospective cohort study. Associations between groups and baseline characteristics were assessed using <i>t</i> tests and chi-square tests. Logistic regression was performed to evaluate the increased risk of PPH. All analyses were conducted using R version 4.3.3. <b>Results:</b> Of 15,549 women who gave birth, 6487 met the inclusion criteria; 485 (7.5%) were diagnosed with mild thrombocytopenia, whereas 6002 had normal platelet counts. Women with mild thrombocytopenia had a threefold higher risk of PPH (adjusted OR: 3.74; 95% CI: 1.36-10.30) compared to those with normal platelet counts. They were also more likely to require blood transfusions and experience a >4 g/dL drop in hemoglobin level (adjusted OR: 2.28 and 2.99, respectively). In the subgroup analysis, women with immune-related thrombocytopenia had lower platelet counts than other groups from the third trimester to 2 months postpartum. However, primary and secondary PPH outcomes did not differ significantly among the subgroups. <b>Conclusions:</b> Mild maternal thrombocytopenia before cesarean section was associated with a higher risk of PPH compared to normal platelet counts; however, the overall prognosis was similar regardless of the underlying cause.