It is not necessary to stop breastfeeding for fertility treatments.
The problem is that some of the treatments may decrease the milk
supply considerably.  But why assume they will?  Maybe they will and
maybe they won't.  If they do, the baby might wean, but might not,
depending on why he breastfeeds.  Just as some babies wean when the
mother becomes pregnant, but others don't.

Jack Newman, MD, FRCPC