Perusing fertility forums turns up a lot of interesting questions about the female reproductive cycle. Whether they’re trying to conceive or hoping to avoid having a baby, “Can you get pregnant on your period?” is a surprisingly common question–with an unexpectedly complicated answer.
Period Sex and Pregnancy
I’ll admit, the first time I saw this question, I was skeptical. Most women take it for granted that their menstrual period is the only time of the month when they’re basically guaranteed not to get pregnant.
You ovulate once a month, approximately two weeks before your period begins. The egg only lives 12-24 hours, and sperm need to reach the egg during that window in order for you to conceive. Sperm, meanwhile, can live in the uterine environment for up to 5 days, so that’s the length of your functional “fertile window” each month.
If your periods last about 4-7 days, and your cycle is 28 days or longer, the chances that you can get pregnant from period sex are basically zilch. A 28-day cycle means you’d ovulate on day 14. If your cycle is 30 days, ovulation day would be more like day 16. The first day of your period is day 1, so even if you had unprotected sex on day 6 or 7, and the sperm survived the full 5 days, that still only takes you to day 11 or 12, too early for ovulation.
The thing is, not all women fit the 28-day mold. Normal menstrual cycle length can be as short as 21-24 days. For women with these shorter cycles, ovulation falls earlier, too. If you’re ovulating on day 10 or 11, it’s possible that sex during the tail end of your period can result in live sperm in place on ovulation day.
When Your Period Isn’t Your Period
“That time of the month” isn’t necessarily the only time you’ll find yourself reaching for a pad. Some women experience vaginal bleeding between their menstrual periods, and it’s possible for this blood to be dark and heavy enough to mistake it for an actual period. Sometimes, this “breakthrough bleeding” coincides with ovulation.
You see where we’re going with this: Women with breakthrough bleeding may be at their most likely to get pregnant if they have sex at that time!
It’s important to pay attention to your menstrual cycle, because changes can be a sign of other health conditions. Try tracking your period so you learn your body’s typical cycle length, how long your period lasts, and whether you spot or bleed at different points in your cycle. Especially if you’re noticing red blood or enough to need a pad or tampon, let your doctor know, too. Some cervical or uterine issues can cause breakthrough bleeding, and you should get checked out.
The Bottom Line
If it’s the first day or two of your period and you’re feeling up for sex, it’s extremely unlikely that you’ll conceive. Your body’s natural shedding of the uterine lining is going to flush out some of the sperm. More importantly, you’re almost certainly too far from ovulation to have surviving sperm left by the time you release an egg cell. (If your cycle is shorter than 21 days, talk to a doctor.)
Toward the end of your bleeding, especially if you have short cycles and longish periods, you’re in more of a gray area. Period sex isn’t optimum timing to try for a baby, so don’t rely on it if you’re hoping to conceive. But don’t assume you’re in the clear because you’re spotting, either. If you’re not ready to have a baby, your safest course of action is to use protection every time.
