Can I get pregnant on my period? If you’ve ever asked yourself that question, don’t worry: You’re not the only one wondering.
Whether you’re trying to conceive or actively trying to avoid conception, knowing when you’re fertile enough for sperm to meet egg and make a baby can be confusing. Even if you got an A+ in health class, our bodies are all different, and that means the cycle of one woman, transgender man, or non-binary person can be ever-so-slightly off from their peers, making that exact moment when you might experience a pregnancy different from your best friend.
The short answer? Yes, it is entirely possible to get pregnant on your period.
If you are flashing back to health class and thinking hey, wait a second, we hear you. The longer answer is yes, but…
Can you get pregnant on your period?
No matter what your high school best friend always said, there is no one time of the month when it’s 100 percent guaranteed that you can have unprotected sex with no repercussions. The risk of sexually transmitted infections aside, there is a risk of pregnancy—albeit a slight one—that comes with period sex.
If you’re wondering how it can happen, it all has to do with the timing of your menstrual cycle.
A “normal” (meaning typical of most folks) cycle lasts anywhere from 27 to 35 days, says Mary Fleming, OB-GYN and attending physician at Einstein Medical Center Montgomery in East Norriton, Pennsylvania. Day one of a menstrual cycle is considered the first day of your period (or the day you start bleeding). Your cycle then continues for that 27 to 35 days until a new cycle begins with the arrival of your next period.
For most people, a period lasts about three to seven days, Fleming says. Counting ahead, in most folks, ovulation occurs about two weeks later (anywhere from 10 to 17 days into the cycle). “Ovulation is the process of the ovary releasing the egg and its migration through the fallopian tubes,” Fleming explains.
Of course, it takes an egg for someone to get pregnant, as conception happens when a sperm and egg come together and form an embryo. That period of ovulation is also referred to as your fertile window, the one time in your cycle when you are most likely to get pregnant.
Do a little math, and it seems hard to imagine how someone could possibly get pregnant during their period, right? Ten days, which marks the early end of a fertile window for the average person, is at least three full days after the seven-day mark, which again marks the outset for most women’s cycles! Well, this is why it’s rare to get pregnant on your period.
But rare doesn’t mean it never happens, Fleming says. The most likely reason for someone to get pregnant during their period? A menstrual cycle that’s different from the norm.
“The most likely explanation for those women who conceive when they are on their period is that those women are not having regular ovulatory cycles,” Fleming says. “These women may bleed sporadically, have intermittent spotting, or bleed for long periods of time. This typically means they are not ovulating or ovulating unpredictably.”
Even in women who do have regular menstrual cycles, studies have found that estimating your fertile window may not be as easy as counting ahead 10 days after the menstrual cycle begins. According to one study performed by the Biostatistics Branch of the National Institute of Environmental Health Sciences, “In only about 30 percent of women is the fertile window entirely within the days of the menstrual cycle identified by clinical guidelines—that is, between days 10 and 17.”
In other words, it can fall earlier, putting fertility closer to the period when someone is still bleeding.
Getting pregnant “during your period” may also happen when you confuse your period with bleeding from some other condition.
For example, Fleming says, cervical or endometrial polyps may cause bleeding from the vagina, as can cervicitis (an infection of the cervix) or vaginitis (an infection of the vagina such as yeast or bacterial vaginosis) or even micro-tears in the vagina due to vaginal dryness.
If someone assumes that they’re bleeding because of their period but has not actually reached that point in their menstrual cycle, the risk of pregnancy from unprotected sex goes up.
How to Avoid Pregnancy on Your Period
If your goal is to prevent pregnancy, there are a number of birth control options to consider, all of which should be used straight through your period.
The IUD, birth control pill, and other contraceptives can all make period sex safer—at least when it comes to pregnancy risk. To protect against STIs, always use a condom.
What if you want to get pregnant?
If you are trying to conceive, skipping birth control is a big start, but don’t depend on period sex to get you there, Fleming says. Because it’s rare, she still recommends determining your fertility window and having sex more often during that time.
“You will need to determine when you ovulate by keeping a menstrual calendar with a mobile app, basal body temperature charting, or a commercial ovulation predictor kit,” she suggests. “The first day of bleeding is day one. Once you know the length of your cycles (day one to day one), count backwards 14 days.”