A hematoma is a collection of blood that has gathered outside of a blood vessel or organ. During pregnancy, this refers to a pooling of blood within the layers of the uterus. This condition is relatively common, especially when detected during the first trimester, and often prompts medical evaluation. The presence of this pooled blood, or hemorrhage, indicates a separation of the membranes supporting the pregnancy from the uterine wall.
Understanding Hematomas in Pregnancy
The most frequently encountered type is the Subchorionic Hematoma (SCH), also called a subchorionic hemorrhage. This hematoma forms in the space between the uterine wall and the chorionic membrane, the outer layer of the sac surrounding the fetus. The chorion is meant to be firmly attached to the inner lining of the uterus; the blood pocket forms when a partial detachment occurs.
SCHs are the most common cause of bleeding in the first half of pregnancy, occurring in approximately 7% to 27% of pregnancies detected by ultrasound. These collections are usually found adjacent to the developing placenta but are separate from it. Less common and more concerning types include retroplacental hematomas, which form directly behind the placenta, indicating a significant separation of the placenta itself.
Factors Contributing to Formation
The precise reason a Subchorionic Hematoma forms is often not definitively known, making its development a subject of ongoing research. The most accepted theory is a failure in the initial attachment process, often called defective implantation. This can lead to a slight separation of the chorionic villi—the projections that connect the chorion to the uterine lining—causing small blood vessels to rupture.
Several factors are thought to increase the likelihood of developing SCH. These include pregnancies achieved through In Vitro Fertilization (IVF), a history of recurrent miscarriage, or structural abnormalities of the uterus. The use of blood-thinning medications may also contribute to the size or persistence of the bleeding.
Systemic factors may also play a role. Abnormalities in the mother’s blood clotting function or the presence of specific autoimmune conditions are potential underlying causes. Additionally, a history of pelvic infection or elevated blood pressure in early pregnancy has been statistically associated with an increased incidence of SCH. However, many individuals diagnosed with a subchorionic hematoma have none of these identifiable risk factors.
Recognizing Signs and Diagnosis
The most common sign leading to the discovery of a subchorionic hematoma is vaginal bleeding, ranging from light, brownish spotting to heavier, bright red flow with clots. This bleeding is typically painless, though some individuals may experience mild abdominal cramping or pelvic discomfort. A hematoma can also be discovered incidentally during a routine ultrasound scan, even if no external bleeding has occurred.
Diagnosis is definitively made using ultrasound, most often via a transvaginal approach, which provides a detailed view of the uterine structures. On the image, the hematoma appears as a crescent-shaped area of fluid—either hypoechoic (darker) or anechoic (black)—situated between the uterine wall and the gestational sac. The size of the hematoma is measured and compared to the size of the gestational sac; this comparison is a key factor in determining the management approach and prognosis.
Managing the Condition
Management of a Subchorionic Hematoma is primarily centered on expectant management, which involves close monitoring rather than active intervention. This strategy is based on the fact that the majority of these hematomas, particularly those that are small or moderate in size, resolve spontaneously as the pregnancy progresses. Follow-up ultrasounds are typically scheduled to track the size of the blood collection and ensure the viability of the pregnancy.
Providers commonly recommend activity restriction, often referred to as pelvic rest, to avoid aggravating the bleeding. This includes refraining from sexual intercourse, avoiding strenuous exercise, and limiting heavy lifting. Maintaining adequate hydration is also advised to support overall uterine health and reduce the possibility of uterine contractions. While a diagnosis can cause anxiety, the overall prognosis is favorable, with most small-to-moderate hematomas resolving completely and leading to a healthy pregnancy outcome.