What are the chances of getting pregnant while breastfeeding an 18 month old and menstural cycle has not returned?

It's possible: An18 month old has usually decreased their mild intake enough that your hormones have adjusted enough to start you ovulating again, but not necessarily return of your period. I have a 28 year old son that was conceived while solely breast feeding 6 months post-delivery! so if you are having unprotected intercourse, you certainly can get pregnant.