Platelets in pregnancy: Their role and function in disease
Platelets are critical to normal haemostasis and help limit blood loss following vascular injury. In pregnancy, they become increasingly important in preventing excessive bleeding during and immediately following birth. Platelets undergo several changes to adapt to the specific requirements of pregnancy and to facilitate a pro-thrombotic state. Despite the enhanced role of platelets in effective haemostasis, changes in platelet function may also be associated with adverse medical conditions. Such conditions range from mild (e.g. gestational thrombocytopaenia) to severe (e.g. pre-eclampsia and thrombotic thrombocytopaenic purpura). This article discusses changes in platelet function and their role in the development of pathological conditions during pregnancy.
Platelets are ‘anucleate’ cell fragments that circulate in the blood and are critical for haemostasis (Figure 1). They usually exist in a quiescent state but upon vascular injury they become activated and adhere to damaged vascular walls in order to limit bleeding (Linden, 2013). Conversely, defective platelet activity is associated with increased bleeding. During pregnancy, platelets undergo several changes to offset the increased blood loss during birth and the immediate postpartum period.
The usual range of platelet count is between 150–400 × 109/L, with a mean value around 260 × 109/L, although this can vary with age (Biino et al, 2013). Due to increased consumption in pregnancy, the platelet count falls, with statistically significant reductions noted in the third trimester. This fall is greater than reductions seen in both the first trimester and 8 weeks postpartum (Karlsson et al, 2014).
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