Unprotected sex before her period, chance of pregnancy?

Patient: Dear Doctor,My name is James and I am 20 years old. Me and my girlfriend were having sexual intercourse this last Thursday, April the 2nd, and the condom broke so I finished inside her (not all of it, less than half). My girlfriend did not take the Plan B pill because I think it is very bad for her, and because she told me that her period was supposed to arrive the next day, and so it did. Her period arrived that Friday, April the 3rd in the afternoon. I wanted to know if there is any possibility of her getting pregnant?Thank you for all your help, and I hope to hear from you as soon as possible, as I am very very worried.Best regardsJames

Symptoms: None

Doctor: Hi,Thanks for the query.I understand your concern.Usually, in case of regular 28 to 30 days menstrual cycles, ovulation is not expected to occur one day before the menstruation.And also as she got her regular periods on expected date, if she is having normal menstrual flow as usual, the possibility of pregnancy is very less in your case. Do get a pregnancy test done after 1 week to confirm that she is not pregnant.Hope this was helpful, Feel free to discuss further.Take care.