Lots of misinformation and anecdotal stories exist on the internet when it comes to pregnancy and fertility. One question that often comes up: If you’ve had sex during your period, can you get pregnant?

The menstrual cycle is the monthly process by which the body prepares for the possibility of pregnancy. The length of the menstrual cycle will vary from person to person. The average cycle lasts around 28 days, although it’s normal for regular cycles to be shorter or longer, ranging 23 to 35 days, per the National Health Service. During the ovulation phase, an egg is released from the ovaries, and the egg awaits fertilization by sperm. 

To help you make informed decisions about your sexual health, here’s a brief refresher on what you need to know about periods, pregnancy and more.

Can you get pregnant on your period?

“It's not very likely, but still possible,” says Dr. Gina Frugoni, MD, an assistant professor of Obstetrics, Gynecology, and Reproductive Sciences at UC San Diego School of Medicine and obstetrician/gynecologist at UC San Diego Health.

The likelihood of getting pregnant on your period will depend on a couple of factors, such as how regular your menstrual cycle is, “and if the bleeding that [you’re] having is actually a period, or another cause of upper or lower genital bleeding,” she says.

Additional factors include the exact timing of intercourse during your period, and how long your period lasts, Frugoni says.

When is the most likely time to get pregnant?

“The most likely time to get pregnant is around the time of ovulation,” Frugoni says. This usually happens approximately 14 days before the next period, although this will differ from person to person.

If you’re looking to measure when you’re going to ovulate, there are over-the-counter ovulation tests. Ovulation predictor tests can indicate whether ovulation is about to occur by detecting the presence of luteinizing hormones (LH), Frugoni explains.

Progesterone blood tests can be used to determine if ovulation has already occurred, Frugoni adds.

When is the least likely time to get pregnant?

If someone is ovulating and has regular menstrual cycles, the least likely time to get pregnant is at the very end of the cycle when it is past the point that fertilization could occur, and the uterus is preparing to have the next period. However, “it’s sometimes really hard to pinpoint when that timing is,” Frugoni says.

“The very beginning of the period is also a [less] likely time to achieve conception,” she notes, because it takes the body anywhere from 10 to 21 days to produce the next egg.

Can you get a full period and still be pregnant?

When bleeding during pregnancy occurs, you may “presume that it's a period, when it may be actually something else,” says Frugoni.

“There can be a lot of causes of bleeding in very early pregnancy that people interpret as a period,” Frugoni says. “But, it's not the same process as the endometrium dying and shedding.”

Up to 25 percent of people experience bleeding during the first stages of pregnancy, per WebMD. According to the American College of Obstetricians and Gynecologists, light bleeding that occurs in early pregnancy is often not a cause for concern. However, it can be an indication of a more serious condition.

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During the first trimester of pregnancy, it’s common for spotting to result from cervical changes. Light bleeding can also be caused by the implantation of the embryo in the uterus. However, more serious reasons for bleeding during the early stages of pregnancy include miscarriage or ectopic pregnancy, per the National Health Service.

Bleeding during the second and third trimesters of pregnancy may indicate a serious concern. Bleeding may point to preterm labor, placenta previa, placental abruption or a miscarriage. Rarely, bleeding may indicate a uterine rupture or vasa previa, per Healthline.

If you are experiencing bleeding during any point in pregnancy, it is important that you speak with your doctor to determine the underlying cause.