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Subchorionic hemorrhage occurs when there is perigestational hemorrhage and blood collects between the uterine wall and the chorionic membrane in pregnancy. It is a frequent cause of first and second trimester bleeding.
It typically occurs within the first 20 weeks of gestation. When seen in the first 10-14 days of gestation, they are also termed implantational bleeds.
- crescentic collection with elevation of the chorionic membrane
- depending on the time elapsed since bleeding, the collection will have variable echotexture
- acute: hyperechoic and may be difficult to differentiate from the adjacent chorion
- subacute-chronic: decreasing echogenicity with time
- in almost all cases there is an extension of the hematoma towards the margin of the placenta 3
In early pregnancy, a subchorionic hemorrhage is considered small if it is <20% of the size of the sac, medium-sized if it is 20-50% 9, and large if it is >50-66% of the size of the gestational sac 5.
Large hematomas by size (>30-50%) and volume (>50 mL) worsen the patient's prognosis 9.
Treatment and prognosis
Fetal outcome is dependent on the size of the hematoma, maternal age, and gestational age 2. In most cases, the hematoma gradually decreases in size on follow-up and can resolve over 1-2 weeks 9. A subchorionic hemorrhage places the gestation at increased risk of:
If the collection extends to the internal os and/or there is dilatation of the internal cervical os, this is an indication of extremely poor prognosis, almost always leads to impending miscarriage.
General imaging differential considerations include: