The claim: You can’t get pregnant during your period, or during perimenopause.
The facts: While pregnancy during menstruation or perimenopause is relatively unlikely, there are plenty of women who can tell you that it’s not impossible.
Let’s talk about menstruation first. Since ovulation occurs at least several days after the start of a woman’s period—on average, around day 14, but ranging from days 11 to 21—the odds are against getting pregnant if you have sex while you are actually having your period. But there are exceptions. If you tend to have a shorter menstrual cycle—every 21 to 24 days instead of the typical 28 to 30 days, for example—then having sex during your period just may result in pregnancy.
Here’s how it might work: Say that you have sex right at the end of your period. In the right conditions, sperm can live inside a woman’s body for as long as five days. So with a short cycle, one of those long-lived sperm could fertilize an egg your body releases four or five days after you had intercourse.
As for perimenopause—the years leading up to menopause during which the ovaries gradually begin to produce less estrogen—it’s true that you are definitely less fertile than in your younger years. But that doesn’t mean there’s no chance of becoming pregnant. Perimenopause can last as long as 8 to 10 years, typically beginning when a woman is in her mid-40s. Menstrual periods become less regular, so it’s harder to predict when you might be ovulating. Until you are in full menopause—that is, you’ve gone 12 full months without a single menstrual period—there is still the possibility, although it may be small, of conceiving a child.
In other words, don’t rely on either having your period or being in perimenopause as birth control.