Low-dose acetylsalicylic acid irreversibly inhibits the cyclo-oxygenase enzyme in platelets, thus preventing the synthesis of thromboxane, which causes vasoconstriction and platelet aggregation. By this mechanism low-dose aspirin may enhance ovarian and uterine blood flow and tissue perfusion and thus improve ovarian responsiveness for gonadotrophins and endometrial receptivity for implantation. Randomized controlled studies and meta-analyses on the low-dose aspirin therapy to improve IVF/ICSI outcome or uterine hemodynamics have revealed conflicting results.