Does thinning your blood by taking an aspirin a day make it easier to conceive?
The simple answer is no.
First, it is important to distinguish between low-dose aspirin (75 to 82 mg) and regular-dose aspirin. Low-dose, long-term aspirin use irreversibly blocks the formation of a chemical in platelets called thromboxane A2. This reduces platelets ability to clump together, thus reducing their clotting ability. So, low-dose aspirin does not "thin" the blood but rather acts as a mild anticoagulant. This anticoagulant property makes aspirin useful for reducing the incidence of heart attacks.
There is no data that use of low-dose aspirin will improve the chance for conception in a couple who is trying to get pregnant through intercourse at home.
Many, many studies have been performed using low-dose aspirin in women who are undergoing treatment with in-vitro fertilization (IVF) with mixed results. Some of the studies concluded that low-dose aspirin improved the thickness of the uterine lining or produced higher pregnancy rates. Many other studies failed to find a benefit in either outcome.
Many reproductive endocrinologists utilize low-dose aspirin due to its ease of use, low expense, and lack of any data showing harm to its use. Another area where low-dose aspirin has been used is in couples with recurrent miscarriage. Some women with recurrent miscarriage may have underlying conditions which increase their risk for blood clotting. It is thought that blood clots forming in the uterine blood vessels may increase the risk of miscarriage.
Again, numerous studies have been performed using low-dose aspirin and other anticoagulants in an attempt to reduce the risk for miscarriage. Again, the results are mixed. Physicians also persist in the use of low-dose aspirin for recurrent miscarriage since the studies also did not show any obvious harm in doing so.