I (and at seems many other women) are in a conundrum with regards to breast feeding & IVF.
My example is that we had a successful pregnancy through IVF when I was 41 yrs old (after 3 cycles). My 16 moth old is still breast feeding 3 times daily and we both enjoy it immensely. I would like to try my luck again with IVF (small chance that it may be) but most clinics advise you to stop breast feeding before doing another cycle.
Now I know that breast feeding in its early, frequent stages can stop menstruation - however, this is not the answer I am looking for as I have had regular cycles for over a year now. I have also done enough research to feel comfortable that the drugs used in IVF will not adversely affect a breast feeding baby. There was some web talk about the uterus having contractions when breastfeeding so that may ‘push’ the implanted embryo out? But other than general comments that breastfeeding ‘may’ reduce your fertility rate I can find no research, explanations or reasoning as to why.
Hope some one out there is better at researching this sort of thing than me as it is frustrating (and to many others from posts on the web) to be told to stop breast feeding to do another cycle of IVF when you are running out of time.
Thanks for any insights
Sally
I don’t have an answer for you, but you could ask at this forum. My wife likes to read the information there.
I suspect it’s because not enough women breastfeed and have IVF at the same time so they think it’s unsafe. I know that women get pregnant while still nursing and have no problems.
For any who may be interested in an answer - I just found some comments that suggest that Prolactin (which helps stimulate milk production while breastfeeding) could counteract the IVF drugs that stimulate ovulation. However, I then found a comment from an MD that Prolactin levels go back to normal after a fews months of breastfeeding - but they recommend you stop breastfeeding before IVF anyway! 
http://forums.haveababy.com/index.php?showtopic=115
I talked to my wife when she got home and suggested a book called Medications and Mother’s Milk by Thomas W Hale. She said you can get it on Amazon and he has a web site. He’s supposed to be a leading doctor WRT medications and breastfeeding.
The two big issues are prolactin and oxytocin. Prolactin levels tend to be elevated in nursing mothers, and will need to be reduced by drugs or weaning before implantation. Oxytocin is produced every time the child nurses, and causes uterine contractions; this, I’m sure, is the larger issue in the doctors’ minds.