Subchorionic hemorrhage (subchorionic hematoma) during pregnancy

A subchorionic hemorrhage/hematoma is bleeding or blood within the chorion, which is the membrane just inside the placenta (not the same as the amnion or amniotic fluid sac). Many women experience small subchorionic hemorrhages that do not cause symptoms. Instead they are detected at routine ultrasound visits. In many cases, subchorionic hemorrhage is discovered during a first trimester sonogram (aka ultrasound).

How common is subchorionic hematoma?

Estimates of the number of women that experience subchorionic hematoma vary greatly, from 4 to 48%. As many as one in four women will have abnormal vaginal bleeding during the first third of the pregnancy. The most common abnormality that can occur during this examination is called a subchorionic hemorrhage or subchorionic hematoma.

Risk to the developing baby

Miscarriage. A subchorionic hemorrhage detected in the first trimester increases the risk of having a miscarriage, although hematomas do not pose any risk to the fetus or mother.

• The risk of miscarriage seems to correlate with the size of the hematoma and its position within the uterus. More specifically, the risk of miscarriage in women with subchorionic hemorrhage increases threefold when the volume of blood makes up more than 25% of the gestational sac.
   
• Location of the hematoma may be more critical than its overall size, however. Hematomas located within two areas of the uterus, namely the corpus and fundus, are significantly more likely to be associated with miscarriage then hematomas in the supracervical area. 
   
• There are no specific risk factors for subchorionic hemorrhage; however, in women who have subchorionic hemorrhage, certain groups of women are more likely to have a miscarriage. The risk of miscarriage increases as the age of the mother increases. The risk of miscarriage was twice as high in women older than 35 compared those younger than 35. 

Preterm delivery. Subchorionic hemorrhage found in the second trimester increases the risk of preterm delivery and abruption of the placentae, which is the premature separation of the placenta from the uterus. 

Lower weight babies. Women who have subchorionic hemorrhage during pregnancy give birth to lower weight babies, on average.

Risk to mother 

In most cases, subchorionic hemorrhage poses little to no risk to the mother. Nonetheless, large subchorionic hemorrhage may increase the risk for pregnancy-induced high blood pressure, cesarean delivery, and preeclampsia.

How is subchorionic hemorrhage diagnosed?

By far, the most common means by which subchorionic hemorrhage is diagnosed is by ultrasound. The sonogram can show the presence or absence of a subchorionic hematoma, confirm if the fetus is still living and healthy, and can identify other fetal abnormalities. Ultrasound is also helpful for tracking the size of the hematoma over time, since it uses sound waves instead of radiation, another advantage of ultrasound is that it is portable and can be performed at the patient's bedside.

Unfortunately, ultrasound is not always useful for showing small subchorionic hematomas. As mentioned, small hematomas do not pose any risk to the fetus or mother, so if they are missed it does not negatively influence the course of the pregnancy. However, small subchorionic hematomas may be the cause of abnormal vaginal bleeding and if they cannot be detected by ultrasound, mothers are left without a diagnosis or additional studies are ordered.

Another limitation of ultrasound in the diagnosis of subchorionic hemorrhage is false positives. Uterine fibroids or small contractions of the uterus can give the appearance of subchorionic hemorrhage. Doppler ultrasound can help distinguish some of these features, though.

MRI or CT scans are not often performed on pregnant mothers, including in the diagnosis of subchorionic hematoma. CT scans expose the developing baby to potentially harmful radiation. Use of MRI is limited during pregnancy because the fetus usually moves too much to provide usable images.

Prognosis

Most studies of subchorionic hemorrhage focus on the outcome of the pregnancy in which the hemorrhage formed. It is unclear whether subchorionic hemorrhage in one pregnancy makes it more likely for a woman to experience one in a subsequent pregnancy, though that connection is unlikely. Likewise, if the fetus survives to term after a subchorionic hemorrhage there is nothing to suggest that the child will be developmentally delayed or stunted. If the condition leads to preterm delivery, the long-term complications to the child are related to the preterm delivery rather than the subchorionic hemorrhage itself.

References

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