|Ultrasound showing a subchorionic hemorrhage|
Chorionic hematoma (also chorionic hemorrhage) is the pooling of blood (hematoma) between the chorion, a membrane surrounding the embryo, and the uterine wall. It occurs in about 3.1% of all pregnancies, it is the most common sonographic abnormality and the most common cause of first trimester bleeding.
Cause and diagnosis
- Subchorionic hematomas, the most common type, are between the chorion and endometrium.
- Retroplacental hematomas are entirely behind the placenta and not touching the gestational sac.
- Subamniotic or preplacental hematomas are contained within amnion and chorion. Rare.
Ultrasonography is the preferred method of diagnosis. A chorionic hematoma appears on ultrasound as a hypoechoic crescent adjacent to the gestational sac. The hematoma is considered small if it is under 20% of the size of the sac and large if it is over 50%.
Prognosis and treatment
The presence of subchorionic bleeding around the gestational sac does not have a significant association with miscarriage overall. However, the case of intrauterine hematoma observed before 9 weeks of gestational age has been associated with an increased risk of miscarriage. In one study women who complied with instructions for bed rest for the duration of bleeding had a lower rate of miscarriage and a higher rate of term pregnancy than non-compliant women. The study had several limitations; results were severely confounded by inherent differences between compliant and non-compliant women. 
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