What happens if I take aspirin while pregnant?

Nothing. Nothing should happen if it is a small dose. Do not take it without medical recomandation.
Consult your OB/GYN. I agree aspirin to be taken ONLY if ordered by a physician during pregnancy. I do not agree that "NOTHING" can happen. The FDA states aspirin & other NSAIDS to be Category D though it's true that aspirin's not been formally assigned that designation. We know aspirin can cause cardiovascular complications after 30-32 wks. Also increased bleeding time can occur which isn't optimal when birthing.
Better not to use it. It is especially important that you not use aspirin during the last 3 months of pregnancy unless specifically directed to do so by your doctor, because it may cause problems in your unborn child or complications during delivery.