If the menstrual cycle is brief, say 22 days, women may ovulate merely days following their menstruation. Sperm can live in viable cervical mucus for up to 5-7 days. So, if women ovulate a little earlier than usual, it may be possible for them to become pregnant. The earliest that a woman can expect to get pregnant is about 10 days after her last flow; but most agree that a more reasonable estimate is something like 50 percent by day 15 and 95 percent by day 20 after the start of her period.