| It's not likely, but it can happen. It is possible for a woman to get pregnant from intercourse during her period, especially if her menstrual cycle is brief.
In a 20-day cycle, for example, ovulation — the release of the egg — may very well occur on Day 6 of her cycle. Her period begins on Day 1. It lasts about five days. But a man's sperm can fertilize an egg up to six days in her body. Let's say this couple has unprotected vaginal intercourse in the first two days of her period. The live sperm can wait to join with her egg when it is released on Day 6. This could cause a pregnancy.
It is also possible that a woman may think she is having her period when she is not. It is also possible to get pregnant during breakthrough vaginal bleeding.
It's not only women with short cycles who need to be careful about unprotected vaginal intercourse during menstruation. Even when cycles are long and regular, ovulation may occur on different days in different cycles. That's why abstinence is necessary for several days in a row for women who choose to use fertility awareness-based methods of contraception.
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