Can a woman get pregnant just before her period? The answer is yes, it is possible, but it is not very common. Fertilization usually occurs around the time of a woman's ovulation, which happens between the 12th and 16th days of the menstrual cycle. However, it is still possible to become pregnant later than this time, or just before your period, and there are some reasons why this can happen.
How does ovulation influence when you can get pregnant?
A woman's menstrual cycle starts on the first day of her period and is measured up to the first day of the next period. A woman's monthly cycle is normally 28 to 32 days, although some may have shorter or longer ones.
Ovulation (release of an egg from an ovary) usually occurs between 12 to 16 days from the next period, although many women may ovulate anytime between the 11th to the 21st day after the first day of their last menstrual period (LMP). This is when the woman is known to be fertile, because if sexual intercourse occurs during this phase, the chance of become pregnant is great. Women must remember though, that ovulation may occur at various days during each cycle, meaning that it may occur on different days each month. Your periods come about 2 weeks after you have ovulated.
To become pregnant, fertilization must occur - this is when your partner's sperm unites with your egg somewhere in the fallopian tubes. Since an egg remains viable only 12 to 24 hours after being released from the ovary, the timing of sexual intercourse is important, and this should occur within this time. On the other hand, sperm survives up to 7 days within your body, and as long as you ovulate during the time that the sperm is viable, you can still get pregnant. This means that you have a "fertile window" of 6 days where you can ovulate anytime and your egg can meet the surviving sperm.
Can you get pregnant right before your period?
It is difficult to get pregnant right before your period, since ovulation takes place around 2 weeks before the next period. This is true among women who have regular menstrual cycles and ovulation can be predicted to occur around mid-cycle. However, some women have irregular cycles. If your ovulation takes place later than expected (mid-cycle), say on the 24th day of the cycle instead of around 14th day, and fertilization and implantation take place, then pregnancy can occur right before your expected period. Some women also have episodes of vaginal bleeding that are mistaken for periods but are not actually counted as a menstrual period. Since you may not know when your period is due and you are not sure if a bleeding episode is an actual period, then it may be possible to become pregnant on what you think is a day or so before your menstrual period.
Aside from this, there is another explanation of how a woman can get pregnant before her expected period. A study reveals that it is possible for a woman to ovulate more than once within a menstrual cycle. Canadian researchers found that out of 63 women included in the study, 10% ovulated twice in a month. Their findings suggest an explanation of how one can get pregnant close to the expected period and why some contraceptive methods fail. While most of the participants ovulated only once, a few had two to three waves of maturing eggs that could be released from the ovaries. Their results show that contrary to conventional knowledge about menstrual cycles, women can ovulate more than once a month and can get pregnant even more than once, which coincides with the 10% occurrence rate of non-identical twins.