When you start your period each month, there is no ovulated egg in your fallopian tubes. The reason you begin bleeding is because ovulation occurred but a sperm did not fertilize your egg, so no pregnancy was implanted in the uterus. The thickened endometrial lining of the uterus is now in the process of sloughing. Theoretically, you can’t get pregnant during this sloughing (bleeding), again because there is no egg hanging around waiting to meet a sperm.
But never say never, because in rare instances, having sex during your period might result in a pregnancy. Furthermore, there are other reasons to be bleeding, besides a period. Some women have bleeding during ovulation. Granted, it is usually not as significant a bleed as a menstrual period, but it certainly is not a sure thing.
The National Institutes of Health (NIH) conducted a study in 2005 that found that women could be fertile as early as four days from the start of their menstrual flow; in this study 17 percent of women were fertile by day seven. Your fertile time lasts about one week per month, and after you ovulate your egg is alive for twenty-four to forty-eight hours.
There are times in a woman’s life, such as perimenopause or in teenage years when the menstrual cycle may be irregular, that make it difficult to ascertain whether bleeding is a true menstrual flow or something called dysfunctional uterine bleeding, which means abnormal bleeding due to irregular ovulation.
Take, for example, a woman who has a disorder like polycystic ovarian disease, in which she makes many eggs but none of them ovulates (release of an egg from the ovary). Consequently, she may not experience menses for six months at a time. Bleeding then may occur for two different reasons.
She may have bleeding because she does indeed ovulate and menstrual bleeding follows about fourteen days later. She may also have bleeding because the lining of her uterus is so thickened by the continuous effects of estrogen that she sheds excess lining, which is not technically a true period.
This second situation indicates a time when the woman could become pregnant. If you’re one of those women with irregular menses, please be aware that it will be extremely difficult for you to know when you are ovulating.