What Is a Subchorionic Hematoma?

Bleeding during pregnancy can be alarming but isn't always a sign of an impending miscarriage. Sometimes, bleeding is a symptom of a fairly common type of blood clot or pooling of blood called a subchorionic hematoma (also known as subchorionic hemorrhage), which occurs in 1.7% to 3.1% of pregnancies. Most subchorionic hematomas will go away on their own without causing harm to the fetus or pregnant person.

This type of hematoma is a common cause of vaginal bleeding between 10 and 20 weeks gestation and is caused by "bleeding under one of the membranes (chorion) that surrounds the embryo," according to the University of Michigan Health. The blood clot forms between the placenta and the wall of the uterus and usually will heal itself without adversely impacting the pregnancy.

Although there's nothing that can be done about a subchorionic hematoma, in most cases the bleeding resolves without causing a problem. While some studies have shown that this condition may increase the risk of complications and pregnancy loss, the research is inconclusive. Most people who develop subchorionic hematomas enjoy otherwise normal pregnancies. Learn more about subchorionic hematomas.

Causes of Subchorionic Hematoma

The causes of subchorionic hematoma aren't fully understood. However, research suggests that maternal conditions such as blood clotting disorders, preeclampsia, and trauma, as well as maternal use of drugs that cause blood vessels to dilate (such as cocaine and methamphetamines) could play a role.

Risk Factors of Subchorionic Hematoma

There are some suspected risk factors for subchorionic hematomas. Studies have found they're more likely to occur in pregnancies that are conceived via in vitro fertilization (IVF) or frozen-thawed embryo transfer, for example.

Symptoms of Subchorionic Hematoma

Bleeding caused by a subchorionic hematoma can range from a heavy flow with clots to light spotting to no bleeding at all, in which case the only reason the clot is discovered is that it shows up during an ultrasound.

Vaginal bleeding is estimated to affect as many as one in four people during the first half of pregnancy and is a common reason for first-trimester ultrasonography. Some women also have some cramping, especially if the bleeding is significant.

Complications of Subchorionic Hematoma

Hematomas found during the early part of the first trimester tend to be less problematic than those discovered later in the first or second trimester. And generally speaking, small hematomas on the surface of the placenta are far less concerning than those that develop under the placenta or behind the fetal membrane.

Hematomas that don't grow also are less worrisome, but those that do may cause the placenta to pull away from its attachment site on the uterus. If more than 30% of the placenta becomes dislodged, it could cause the hematoma to grow even larger. This may set off a domino effect in which the membranes (amniotic sac) rupture prematurely, leading to spontaneous abortion.

In fact, research has found that subchorionic hematoma can increase the risk of an array of pregnancy complications, including miscarriage, preterm labor, placental abruption, and premature rupture of membranes.

Treatment of Subchorionic Hematoma

Once a subchorionic hematoma forms there's nothing a doctor can do about it. There's no treatment for these blood clots. However, they can be managed. If you develop one, depending on the location and size of the hematoma, your doctor may have you come in for regular follow-up exams.

You would also be advised to avoid strenuous activity, heavy lifting, or excessive exercise. You may need frequent rest to prevent increases in blood pressure, and your doctor may also recommend against travel.