I personally know several women who have conceived within 2 months after giving birth with no period and they were breastfeeding. Such situations can and will happen. Your best bet is to use protection. Does your wife have and IUD? This is a great form of birth control and you both wouldn't have to worry about condoms or pills or anything.
Women tend to be infertile for a little while after giving birth. This period will be longer if they continue breastfeeding. BUT this is very variable, there is no way to know for any one woman whether she has started ovulating again yet, and as far1079 explains she could be fertile even before her first post-pregnancy period.
So, use some protection!
I'm no doctor but as a woman, ovulation comes before menstation so yeah, there's a chance. There are many women out there who have gotten pregnant just a month after giving birth so I suggest the use of protection if you don't want a back to back pregnancy. Hope this helps