Early ovulation
Typically a woman ovulates around 14 days before the start of her period. So if you have an average 28 day cycle, you would most likely ovulate on cycle day 14. A woman’s cycle, though, is not always predictable. Even women who normally have regular cycles can have an off cycle and ovulate earlier or later than normal. If you ovulate very early in your cycle, for example, on cycle day 10, it would be possible to conceive if you had intercourse while on your period.

Long periods or irregular bleeding
Some women have very long periods or irregular bleeding after their period. If a woman had a long period, say it lasted for 10 days, and she had unprotected sex while she was still bleeding, she might get pregnant. Even though a woman is bleeding or spotting, it doesn’t mean she is not fertile. It is possible for a woman approaching ovulation to still be on her period. In fact, some women will begin producing fertile cervical mucous during the last few days of their periods. If a woman ovulates shortly after her period ends or while she is spotting, she could get pregnant.

Ovulation Spotting
Ovulation spotting is bleeding that occurs close to ovulation. It is very fertile cervical fluid and it is sometimes mistake for a long or abnormal period. Some women will have brown or red spotting right before they ovulate. This type of spotting provides the ideal environment for sperm to live in. If a woman has sex while she is having ovulation spotting, there is a good chance she could get pregnant.