The statistics are that bfing is 98% effective (the same as the pill) during the first 6 months post-partum, provided all 3 of the following conditions are met:

- Exclusively bf - ie no water, formula or food
- Feeds at least once through the night
- AF hasn't returned yet.

So if this is you, you should be fine until the 6 month mark. Then it's time to look at your options!

My personal experience is that I relied on bfing alone for the first months both times, and I didn't fall pg.