Evidence suggests that an imbalance in prostacyclin and thromboxane A2 (TxA2) plays a key role in PE. Aspirin (ASA) has a dose-dependent effect blocking production of TxA2, a potent stimulator of platelet aggregation (PA) and promoter of vasoconstriction. Incomplete inhibition of PA, designated aspirin resistance (AR), can be reduced by increasing the ASA dose.