Subchorionic hemorrhages occur when the placenta detaches from the original implantation site during pregnancy. The pregnancy can still be successful, but it’s still important to see a doctor.

Bleeding during pregnancy is certainly a cause for worry. After all, pregnancy — in theory — shouldn’t cause vaginal bleeding. Still, there are other causes of bleeding besides menstruation. Vaginal bleeding in some form occurs in about half of all pregnancies, according to the March of Dimes.

In pregnancy, some types of bleeding are a big issue, while others aren’t. Subchorionic bleeding is just one type of bleeding. As with bleeding in general, some cases can become serious while others don’t adversely affect the pregnancy. But it’s important to call your doctor right away when you experience any form of vaginal bleeding while pregnant.

Subchorionic bleeding, explained

Subchorionic bleeding occurs when the placenta detaches from the original site of implantation. This is called a subchorionic hemorrhage or hematoma. It affects the chorionic membranes. These lift apart and form another sac between the placenta and the uterus. The movement and resulting clots are what cause this type of bleeding.

These hematomas can range in size, with the smallest being most common. Larger versions can cause heavier bleeding.

How it differs from other types of bleeding

Subchorionic hematomas are just one cause of bleeding in pregnancy. Their precise cause is unknown. They’re also not the same as spotting.

Spotting occurs in about 15 to 25 percent of women during the first trimester, according to the American College of Obstetricians and Gynecologists. While spotting can occur at any stage of pregnancy, it’s most common in the first trimester.

Causes of spotting include:

Spotting is exactly as it sounds — a few spots of blood. While it’s still a good idea to report any form of spotting to your doctor, the symptoms are very different from vaginal bleeding.

Bleeding that goes beyond a few spots and requires a pantyliner is often a sign of something else. Subchorionic bleeding is one such possibility. Bleeding tends to be the only sign or symptom of subchorionic hematoma. You may not even realize you have one until your doctor performs an ultrasound.

Heavy bleeding can also be a sign of:

These more serious causes of vaginal bleeding are also accompanied by other symptoms, such as severe abdominal pain and dizziness.

Is subchorionic bleeding harmful?

Many subchorionic hematomas aren’t harmful in the long term. Your doctor will have a better idea after looking at the hematoma on an ultrasound. Smaller hematomas have better outcomes. Larger versions can present problems.

According to a 2014 study, reports vary on the risk of miscarriage related to subchorionic hematomas with vaginal bleeding. However, the risk does increase during the first half of pregnancy. The earlier you seek a diagnosis, the better the outcome.

Prompt treatment is key

If a diagnosis of vaginal bleeding is deemed subchorionic, then your doctor will likely start treatments to prevent miscarriage. Options may include progesterone or dydrogesterone. If the hematomas are large, you may also be advised to:

  • Stay in bed, on bed rest.
  • Avoid standing for long periods of time.
  • Avoid sex.
  • Avoid exercise.

Follow up with your doctor

Subchorionic bleeding is a sign of a related hematoma. While not considered a normal occurrence in pregnancy, these hematomas aren’t unusual. They also don’t necessarily mean the pregnancy will fail. With treatment and close monitoring, many women go on to deliver healthy babies at full term.

Even though subchorionic bleeding doesn’t pose an immediate threat like other types of vaginal bleeding, you should still follow up with your doctor. Call your doctor whenever you experience any bleeding or spotting. If the cause is unknown, an ultrasound may be performed to rule out hematoma.