Hi - I'm sure I posted in that thread you found, but just in case.
We decided to try IVF/ICSI while DD was nursing at the age of 2.5. I night-weaned her before the cycle, and I was working FT, so she nursed morning and evenings and weekends.
I researched the drugs through Hale (he has some stuff on his forums about them) and because the drugs are not readily bioavailable, with an older baby who is not nursing much, he doesn't see the drugs as particularly problematic. He does state that milk production will probably be affected, and I did notice that. My RE had told us to wean, and I did NOT tell him I was still nursing.
Both cycles last year were negative. The first, I was quite sick (got a stomach bug and then the flu) during the cycle, and then after a good crop of eggs, and a decision for a Day 5 transfer, none of the embryos made it to Day 5. The second cycle was just plain negative.
I could feel my uterus contracting when DD nursed, and I don't know whether that affected anything, or whether it was just plain bad luck. After all, IVF isn't necessarily successful anyway.
This year, after DD weaned completely, we tried another cycle, and it was successful. Again, who knows whether nursing had anything to do with it or whether it was just coincidence. Certainly many mothers get pregnant while nursing - but perhaps if you're borderline anyway (I need very high doses of drugs in order to respond) the nursing can make a difference to hormone level.
It's a bit of a crapshoot. I can't say I regret trying while nursing, although our line of credit does