Is it safe to have unprotected sex 1 day before girlfriends period is going to start?

Not 100% In order to get pregnant, intercourse must occur around the time of ovulation (releasing an egg). Ovulation usually takes place about two weeks before menstruation, which makes it unlikely (but not 100% impossible) you would become pregnant from intercourse around the time of your period. If you are trying to avoid pregnancy, be sure to discuss effective birth control options with your doctor.