Personally I know of a two couples. They did not concieve using IVF but went on to conceive naturally.

1. TTC for 8 years, IVF & everything, then after giving up it all up 3 natural pregnancies with three healthy babies. Age when first pregnant was 38.
2. TTC for 9 months but due to age (mother 36) went straight to IVF, then natural pregnancy 6 months in to IVF while waiting for second IVF cycle - had taken medication for the 'Colorado Protocol'.

Who knows! In the second case I think it could be one of two things, one they probably panicked (due to all the negative cr*p out there about being 'too old' when over 35) and 'rushed' into IVF when they possibly didn't really need to, or the medication used for the Colorodo protocol 'fixed' the problem they had.

In the first case it was a combo of issues that made them 'infertile' but nothing absolute. She ovulates, eggs appraently ok quality, he had some sperm issues. so nothing that couldn't change or right itself possibly.

It's possible that in some cases while undergoing AC couples have 'fixed' their particular issues and that is why they get pregnant naturally afterwards??
or maybe they really are miracles?

Interesting thread, thanks drbeee.