SaraJane, I don't think there's a hard and fast rule. Women fall pregnant successfully in the first cycle after m/c and go on to have their babies. I waited until AF returned before starting TTC and it still took a number of cycles for me to fall pregnant.

After my last m/c, which was a missed m/c at 11 and a half weeks, the obstetrician who performed the D&C told me to "get back on the horse" as soon as I wanted, while my GP advised me to wait until after my AF had returned before dtd without contraception. I was emotionally very raw anyway and I asked to be prescribed Zoloft anti-depressants which I took for a few months until I felt I was able to manage. It took over 8 weeks before AF returned for me (I started using OPKs after 5-6 weeks and temping to see if I could work out what my body was up to!) and then five or six cycles before I was able to fall pregnant again.

After the first m/c which was a blighted ovum, I m/c naturally and AF returned quite quickly. But it took some time for the hormone levels to come back down.

I too have heard that allowing AF to return means that your lining is able to thicken up to allow good implantation. I think it helps to start TTC-ing when you're emotionally ready and only you can know when that is. I waited a cycle both times and falling pregnant again didn't happen straight away anyway.

Good luck with your TTC journey!!

And the Waiting for AF after M/C thread was a Godsend for me!! It really helped so much.