Deciphering Implantation Bleeding: What You Need to Know

A pregnancy test can tell you you're expecting, but the body also shows signs of pregnancy. Although not everyone will experience it, implantation bleeding is an early pregnancy indicator.

Implantation bleeding can occur when the embryo attaches to the lining of the uterus soon after conception. It's a fairly common experience, as well, occurring in about 25 percent of pregnancies. But because of its timing in the menstrual cycle, implantation bleeding can be confused at the start of your period.

Here's what to know about implantation bleeding and how to tell the difference between it and menstrual bleeding.

What is implantation bleeding?

After conception, the fertilized egg travels from the fallopian tubes to the uterus, says Melissa Dennis, M.D., M.H.A., F.A.C.O.G., chief medical officer at Partum Health. The embryo roots in and attaches to the uterus lining (called the endometrium) to grow and develop. This can result in some light bleeding shortly after conception.

Implantation bleeding can be confused for the start of a period if the pregnancy, as it occurs at roughly the same point in the menstrual cycle. After implantation occurs, conception is confirmed with a pregnancy test.

Timing and characteristics

Implantation bleeding occurs about 10 to 14 days after fertilization and usually lasts just a few days, Dennis says. This is roughly the same time in the cycle when a menstrual period begins for many people.

Implantation bleeding is characterized by light bleeding or spotting — typically lighter than period bleeding (though everyone's body and cycles are different).

You may see a few blood spots on toilet paper or in your underwear. The blood is usually brown, dark brown or light pink, not bright red like menstrual blood.

Differentiating implantation bleeding from menstrual bleeding

Implantation and menstrual bleeding have similarities that can make it difficult to distinguish between them.

Implantation bleeding occurs around the same time in a cycle when a period is expected. The spotting and mild cramps that can occur after implantation may be confused with the start of a period.

A menstrual period usually lasts longer than the typical one or two days of implantation bleeding. Implantation bleeding is also much lighter—more like spotting than bleeding. You shouldn't need more than a panty liner with implantation bleeding, says Christine Greves, M.D., F.A.C.O.G., an OB-GYN at Orlando Health Women's Institute Center for Obstetrics & Gynecology.

Causes and mechanisms

"The endometrium is thick and fluffy, with extra blood flow during this phase of the menstrual cycle in preparation for pregnancy," Dennis says. "When the embryo implants into the endometrium, it disrupts the area, sometimes causing some shedding, which appears as spotting or light bleeding."

After the embryo affixes itself to the wall of the uterus, the body starts producing the hormone human chorionic gonadotropin (H.C.G.). H.C.G. supports the pregnancy by keeping the embryo in place and is the hormone that's detected in a positive pregnancy test.

Signs and symptoms

Implantation is a normal sign of early pregnancy. It doesn't mean anything is wrong. In fact, it's a sign the embryo is doing what it's supposed to: attaching to the uterus wall and starting to grow.

Experiencing bleeding during pregnancy can cause some anxiety, but it doesn't necessarily mean the pregnancy is in trouble or there is something wrong.

Along with spotting or light bleeding for a day or two, some mild cramping may also occur. Neither is automatically cause for alarm, Greves says. "Just because you have implantation bleeding, it doesn't mean you're having a miscarriage," she says.

"Listen to your body," Greves adds. "As long as it's just a little blood, a little spotting, and you're not having any pain on either side, then take some deep breaths and mention it to your doctor."

When to seek medical advice

Both experts say that implantation bleeding shouldn't be heavy or painful. Watch for other symptoms, such as fever or dizziness, too. If you experience any of these symptoms while pregnant, seek medical attention right away—even at a hospital emergency room if your regular physician can't see you quickly.

"If you see heavy vaginal bleeding, have abdominal pain or significant or painful cramping, you should see your provider to rule out anything else," Dennis says.

Of particular concern is an ectopic pregnancy. This is when the fertilized egg grows outside the uterus—most commonly in the fallopian tubes. An ectopic pregnancy is not viable and can be a danger to the mother's health, as the fallopian tube could rupture. Surgery or medication is required to remove the embryo in an ectopic pregnancy.

"If you have pain accompanying that bleeding, especially on the right side or left side, then you need to get medical attention," Greves says, "because that's when you need to exclude an ectopic pregnancy."

Experts

• Melissa Dennis, M.D., M.H.A., F.A.C.O.G., an OB-GYN and chief medical officer at Partum Health
• Christine Greves, M.D., F.A.C.O.G., an OB-GYN at Orlando Health Women's Institute Center for Obstetrics & Gynecology