Condom broke during sex, took Plan B about an hour afterwards. Girlfriends period ended a few days before it happened. What are the odds of pregnancy?

Unlikely. Plan B can work in one of three ways depending on where you are in your cycle. It can prevent or delay ovulation, can interfere with the fertilization of the egg or may prevent implantation by altering the lining of the uterus. If you take Plan B One-Step within 24 hours, it is about 95% effective.