What Is a Subchorionic Hematoma?

Written by Nichole Owens
Medically Reviewed by Zilpah Sheikh, MD on April 27, 2025
5 min read

Any type of bleeding during pregnancy can be scary, but it doesn’t always mean there’s a problem. About 25% of women experience some bleeding or spotting during their pregnancy.

In a normal pregnancy, the amniotic sac (where your baby grows and develops) is attached to the wall of your uterus. But sometimes, the sac partially detaches from the uterus, and a pocket of blood forms in the gap. This is called a subchorionic hematoma.

They happen most often between 10 and 20 weeks of pregnancy, and most of the time, they don’t cause problems. They can be large or small.

Subchorionic hematoma size chart

Your doctor will know the size of your subchorionic hematoma based on how it compares to your amniotic sac:

  • Small — less than 20% of the sac size
  • Medium — 20%-50% of the sac size
  • Large — over 50% of the sac size

Doctors aren’t sure, but you may be more likely to develop one if you have or have had any of these conditions:

  • Malformation of the uterus
  • A history of recurrent miscarriages
  • A history of pelvic infections
  • Trauma
  • Early-onset preeclampsia, which is a serious pregnancy issue marked by high blood pressure and organ failure
  • Severe high blood pressure
  • In vitro fertilization

You may notice bleeding (light spotting or a heavy flow) early in your pregnancy. This is often the only symptom of a subchorionic hematoma. Belly pain is rare, but you may have cramps. You might also have a slight discharge.

Sometimes, there are no symptoms, and your doctor discovers it during an ultrasound.

On an ultrasound, a subchorionic hematoma looks like a crescent-shaped space between the amniotic membrane and the uterine wall.

Many subchorionic hematomas go away on their own. If your doctor decides that you do need treatment, they’ll consider several factors, such as how far along you are in your pregnancy and the size of your hematoma. 

Before 20 weeks’ gestation. Your doctor may recommend that you reduce your activity levels and any travel. If you’re bleeding, cramping, or having contractions, they may recommend hospitalization.

After 20 weeks’ gestation. Your doctor will teach you the signs and symptoms of early labor. Your treatment may include

  • A RhoGAM, if you are Rh-negative and your baby is Rh-positive
  • Sonograms about once a month (or more often) to check your baby’s growth
  • Preterm labor treatment if you start having contractions
  • Hospitalization, especially if bleeding occurs after 24 weeks

This condition is common in the first trimester of pregnancy and rarely causes complications. More research is needed, but there is evidence that subchorionic hematomas later in pregnancy may raise your risk of certain complications, such as:

  • Preeclampsia
  • Miscarriage
  • Fetal growth restriction
  • Preterm delivery

“Subchorionic hematoma, although not considered normal in pregnancy, is not an unusual occurrence,” says Eleazar Soto Torres, MD, associate professor and maternal-fetal medicine physician with UT Health Houston, TX. “It is important to let patients know that this does not mean they will lose their pregnancy. The size of the hematoma may be an indicator of prognosis. The majority of these cases deliver healthy babies at term.”

Subchorionic hematomas are only one cause of bleeding during pregnancy. There are other causes of bleeding that range from harmless to dangerous. You should always talk to your health care provider if you experience any vaginal bleeding during pregnancy. 

Cervical changes. Pregnancy causes changes to the cervix that can result in bleeding. You may bleed after having sex, for instance.

Implantation bleeding. Early in your pregnancy, you may experience light spotting. This happens when your baby implants into the wall of your uterus. It usually occurs around the time you would normally have your period.

Ectopic pregnancy. This occurs when the egg implants outside of your uterus, such as in the fallopian tubes. This is a dangerous condition that requires immediate treatment. Other symptoms of ectopic pregnancy can include:

  • Stomach pain low on one side
  • Vaginal bleeding
  • Brown, watery discharge
  • Pain in the tip of your shoulder
  • Discomfort when peeing or having a bowel movement

Miscarriage. Most miscarriages occur in the first 12 weeks of pregnancy. Some symptoms of miscarriage include: 

  • Pain and cramping in your lower abdomen
  • Vaginal discharge or fluid
  • Discharge of tissue from your vagina
  • No longer experiencing symptoms of early pregnancy, such as nausea or breast tenderness

Vaginal infections. These can be diagnosed and treated by your health care provider.

Bloody show. This is when the plug of mucus that has been in your cervix falls out. This usually happens at the beginning of labor. It can happen a few days before contractions start or during labor.

Placenta previa. This is when you have a low-lying placenta near or over your cervix. You may need to go to the hospital for emergency treatment.

To find out the cause of your bleeding, your doctor will discuss your symptoms with you and may do a physical exam. You may also need to have an ultrasound or blood tests done.

A subchorionic hematoma is a pocket of blood that forms when your amniotic sac — the fluid that holds your unborn baby — detaches from your uterus. It’s one of the most common causes of bleeding in early pregnancy and normally doesn’t cause problems. Most of the time, they go away on their own. If you have a large subchorionic hematoma, your doctor will create a plan to treat your condition.

How long do subchorionic hematomas last?

Many heal on their own over time. If your doctor decides you need treatment, they’ll create a plan that considers your symptoms, how far along you are in your pregnancy, and the size of the subchorionic hematoma.

Can a subchorionic hematoma cause a miscarriage?

Sometimes, but it’s important to remember that most of the time, these don’t cause problems.

How can you prevent a subchorionic hematoma?

“There isn’t a way to prevent a subchorionic hematoma,” says Kyle Graham, MD, board-certified OB-GYN and medical director at Pediatrix Medical Group in San Jose, CA.

“Avoiding situations that put stress on the placenta, such as maintaining proper blood pressure, avoiding abdominal trauma, wearing your seat belt correctly, and consulting your physician if you are on blood thinners, can help,” Graham says.

How long does a subchorionic bleed last?

It depends. Most often, your body will heal itself. Talk to your doctor if you have concerns.