subchorionic hemorrhage

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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.

Epidemiology

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.

Radiographic features

Ultrasound 
  • 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
Quantification

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% , and large if it is >50-66% of the size of the gestational sac .

Large hematomas by size (>30-50%) and volume (>50 mL) worsen the patient's prognosis .

Treatment and prognosis

Fetal outcome is dependent on the size of the hematoma, maternal age, and gestational age . In most cases, the hematoma gradually decreases in size on follow-up and can resolve over 1-2 weeks . A subchorionic hemorrhage places the gestation at increased risk of:

If the collection extends up 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.

Differential diagnosis

General imaging differential considerations include:

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