Why is it unlikely to get pregnant when you have sex while on your period?

Ovulation: It is very important to learn the basics of human reproduction. Ovulation occurs about 14 days before your menstrual cycle. Sperm must be present to fertilize the egg. Consider doing some reading on the topic of human reproduction so that you can make informed decisions about your future and your sexuality. Start birth control if sexually active.

Several reasons: sex during a period has been used a part of natural family planning for decades. On a cycle, the uterine lining is shedding and not able to implant an egg that is fertilized. Also, during a cycle, ovulation is not occurring but usually occurs 2 weeks BEFORE the period. This only is true for women with regular and predictable cycles. If you have irregular cycles, this method may not work well.