I agree with the previous poster that it is possible, but unlikely, to ovulate during
one's period. But something else to also keep in
mind -- pulling out doesn't work. The secretions the man has at the beginning (enough to get ... um,,, shall we say, upright) also have the capacity to get a woman pregnant, whether he pulls out before orgasm or not. Do talk to your girlfriend, not just "do you think you're pregnant?