Maybe. Generally speaking, exclusive nursing can help prevent pregnancy. Here's why: Prolactin, the hormone that stimulates the production of milk, also prevents eggs from maturing and becoming fertilized. But know that this isn't a foolproof birth control system — you could start ovulating before you get your first postpartum period, which would mean you were fertile.
So always use a backup method if you're not ready for baby number two just yet. Condoms, diaphragms, nonhormonal intrauterine devices (IUDs), cervical caps and vaginal sponges are all safe forms of birth control for breastfeeding mamas. Talk to your doc about the right backup method for you.