If you’re going to do the deed when you’re menstruating, keep in mind that sexually transmitted infections may be more easily transmitted when there’s blood involved. You also can’t trust that you’re not fertile during this time, so it’s not safe to count your period as birth control. Occasionally, women do ovulate while they are still bleeding. Condoms can decrease your risk of both. If you’re not worried about pregnancy or infection, you’re safe to go at it.