Can you get your period but still be pregnant

Whether you're trying to become pregnant or trying your hardest to avoid it, you can usually take your period as a sign that you don't have to think about a baby anytime soon. But, in a new interview with InStyle, Serena Williams says she actually got a period during the early stages of her pregnancy—and she was completely floored to find out that she was actually pregnant.

In the interview, Williams says that she didn’t think it was even possible that she could be pregnant. She hadn’t seen her now-husband Alexis Ohanian “in like four weeks” and “literally had a cycle just before.” Williams says she took the test “just to shut my friend up” and was completely surprised when it was positive. She was even more shocked when her doctor told her she was seven weeks along. Oh, and she was playing in the Australian Open at the time.

Having your period when you're pregnant is pretty darn unlikely.

“I have heard from some women who say they had periods throughout their first trimester,” Jonathan Schaffir, M.D., an ob-gyn at the Ohio State University Wexner Medical Center, tells SELF. “But in reality, physiologically it’s pretty impossible to have actual periods during pregnancy.”

Just a little refresher: Every month (if you're ovulating), the lining of your uterus thickens and an egg makes its way from one of your ovaries through the fallopian tubes. If it comes in contact with sperm, the sperm can fertilize the egg. If fertilization happens, the egg will continue its journey to the uterus and can implant on that lining. If things continue from there, the fertilized egg becomes an embryo (and, later, a fetus) and the placenta will develop from the uterine lining.

But, if the egg doesn't get fertilized, your body sheds that built-up uterine lining through your vagina, causing a period. And, as you can probably guess, it's kind of an either/or situation—either the egg is fertilized and the process of pregnancy begins, or it isn't and the process of your period begins instead.

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That said, there are several situations that can cause period-like bleeding early in pregnancy.

If you get your period at the usual time, it lasts for the usual amount of days, and the amount of blood that you see is pretty typical for you, it’s pretty unlikely that you’re pregnant, G. Thomas Ruiz, M.D., lead ob-gyn at MemorialCare Orange Coast Medical Center in Fountain Valley, California, tells SELF. But you could have bleeding in early pregnancy that just so happens to coincide with when your period is due, Dr. Schaffir says. In fact, up to 30 percent of pregnant people have some form of bleeding in early pregnancy, according to the American Pregnancy Association.

For instance, you might experience implantation bleeding, which is light spotting or bleeding that can happen when the embryo burrows into your uterine wall, and can also be a cause of bleeding in early pregnancy. But Dr. Ruiz says it’s unlikely this would be mistaken for a normal period because it tends to be much lighter.

Or you might have a cut or tear in your vagina, inflammation of your cervix, or irritation of your cervix from an infection that causes bleeding, Dr. Schaffir says. It can even be caused from sex: “Sometimes women have blood vessels close to the surface of the cervix and, during sex, the friction causes a little bleeding,” he explains. However, again, these usually produce far less blood than a period.

The placenta can also be a cause behind the bleeding if it starts to tear or separate a little. Early in pregnancy, you might see bleeding due to something called a subchorionic hematoma, which is when blood gathers between your placenta and the wall of your uterus, Dr. Schaffir explains. Although the condition can raise your risk for a miscarriage, research suggests that most who have it go on to have a healthy pregnancy.

So what if you really truly thought you got a period while you were pregnant? It's possible that you can actually shed part of your uterine lining after you get pregnant in what's called "decidual bleeding." When you become pregnant, the embryo will implant in one side of your uterine wall, usually at the back, Dr. Ruiz says. But your uterine lining has still built up all over your uterus at that point, and it’s possible for the lining to shed just from the other side of the uterus, he explains. This can look a lot like a period.

In some cases, bleeding during pregnancy can be a sign of a serious issue. So if you're not sure what's causing it, definitely check in with your doctor.

As SELF reported previously, if your bleeding is particularly heavy, comes with abdominal pain, or lasts for more than a few days, that's a sign something more serious may be going on. You might be experiencing an ectopic pregnancy (a condition in which the fertilized egg implants outside the uterus) or a miscarriage.

According to the Mayo Clinic, you should tell your doctor at your next regular appointment if you have any light spotting that goes away within a day. But if you have bleeding that lasts for more than a day, you should contact them within 24 hours. And if you pass any tissue from your vagina, experience moderate to heavy bleeding, or have bleeding along with abdominal pain, chills, or cramping, you should get in touch with them immediately. But, again, many cases of bleeding during early pregnancy aren't serious.

And, on the other hand, if you're not sure if you're pregnant and notice you’re having a period that comes at a weird time, isn't as heavy as usual, doesn’t last as long as usual, and comes with any other pregnancy symptoms, it’s worth taking a test, just in case.

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