Platelets in pregnancy - protector or adversary?

Pregnancy places increased demands on the maternal haemostatic system where it must maintain a balance between bleeding and thrombosis. Platelets are crucial to this process. Platelets support placental development and secrete bioactive mediators that influence trophoblast invasion, vascular remodelling and innate immune crosstalk (platelet-leukocyte and complement interactions). Normal pregnancy is characterised by a gradual decrease in platelet count with advancing gestation. This mild thrombocytopenia toward term is driven by haemodilution, placental sequestration and platelet activation. However, excessive platelet activation can trigger thrombo-inflammatory response linked to the development of pre-eclampsia and foetal growth restriction. Platelet dysfunction and inherited thrombocytopenia may increase the risk of postpartum haemorrhage without directly affecting the pregnancy. Platelets therefore play a dual role in pregnancy where controlled activation is protective but uncontrolled stimulation leads to obstetric complications. An appreciation of this informs preventive strategies such as low-dose aspirin in high-risk pregnancies and individualised management of thrombocytopenia in selected cases.