Even though 'they' say its safe to rely on b/f as 99% effective when b/f fully within the first 6 mnoths (incl overnight), i too would never rely on this....
I have fallen pregnant both times whilst breastfeeding (after 6 months, but under 12 months). First time i had not had AF post partum, and we just happen to DTD around that first time i happened to Ovulate.....and whammo....pg with #3.