Red Lady, the theory behind the aspirin is that it thins the blood. The two main causes of miscarriage being auto-immune problems and blood clotting problems. The aspirin is used to help prevent the blood clotting too much and causing miscarriage. Your blood tends to clot more in pregnancy normally, and for some women this can become too much. Baby aspirin is a low-dose aspirin tablet (much lower than the dosages used for pain relief) that is also often used for people with heart conditions who need to be wary of clots.

I have also noticed that in the US, IVF clinics tend to use it as standard procedure even when there is no evidence indicating a need for it.

I don't think taking aspirin is going to be a magic-bullet that should be given to everyone. I don't think taking aspirin without being advised to is necessarily a good idea either.

That said... after three miscarriages, my FS sent me for more testing and said everything came back normal. However, he did give us a copy of the actual results, and one of mine was sitting at 1.1, when anything 1.2 or higher was considered to be problematic (too early, can't remember exactly which one it was!). I discussed this with the lady I had been seeing for acupuncture for over a year, and we both decided that adding aspirin into the mix would be a good idea for me. She is of the opinion that my body over-responds to things, and a blood level that would be ok for a "normal" person isn't necessarily ok for me. I took aspirin from my next transfer, without telling my doctor (who doesn't really believe in treating things on the off-chance, only if there is overwhelming evidence - I decided my three previous miscarriages were overwhelming enough for me!), and was lucky enough to have that transfer work... At my first consultation with my OB, we talked about my history and the medications I was on, and she had absolutely no issues with me being on aspirin after hearing about the circumstances surrounding my miscarriages. It was a situation where one doctor would, one doctor wouldn't... Sometimes you have to make the medical decisions for yourself, but I certainly wouldn't jump in and take it without some sort of evidence to support it. It may be a commonly used drug that's available over the counter, but it's not without its problems and side effects.

BW