All I have is my own experience. I don't have the sources anymore, its been a long time...I had 2 m/c's in a row. The first was at 13.5 weeks, and the second was at 6 weeks. (About 6 weeks after the second one my DD was conceived, she was full term & perfectly healthy, although I was terrified the entire pregnancy of losing her too.)
Main things I remember:
Around here, they do not start doing any sort of tests to figure out why you are miscarrying until you've lost 3 in a row. Until you lose 3, they basically consider it a fluke. (Grrrrr....)
If you have carried a child to term before m/c'ing, you are less likely to have more than 2 repeat m/c's. (this is what they told me when I wanted testing after only 2 m/c and my dr refused.)
There is no medical reason to wait to TTC after a miscarriage, if you are otherwise healthy. Dr's will tell you to wait until you've had between 1-12 regular cycles for their convenience is figuring your EDD--a friend of mine m/ced within days of me, and we both independently came to this conclusion.
If you have never carried to term and miscarry early, it could be a problem with not enough progesterone, or lutenizing hormone. You can get progesterone cream OTC, and it will not harm the fetus-but if this is not the problem, it may delay an unavoidable miscarriage.
Some early miscarriages are caused by blood that is too thick-this is one of the things they test for after 3, how much your blood coagulates.