What is a subchorionic hematoma?

Subchorionic Hematoma

A subchorionic hematoma (SCH) is a collection of blood that forms between the chorion and decidua basalis due to separation of these layers, commonly detected by ultrasound as a hypoechoic or anechoic crescent-shaped dark area. 1

Definition and Appearance

• SCH represents blood accumulation between the chorion (fetal membrane) and decidua basalis (maternal tissue), creating a space that can be visualized on ultrasound 1
• On ultrasound imaging, SCH typically appears as a crescent-shaped fluid dark area with hypoechoic or anechoic characteristics 1
• SCH is commonly detected during ultrasound evaluation of first trimester vaginal bleeding, occurring in 7% to 27% of pregnancies 2

Diagnosis

• Transvaginal ultrasound is the primary imaging modality for diagnosing SCH, especially in early pregnancy 2
• SCH is typically identified as a crescent-shaped collection between the gestational sac and uterine wall 1
• All SCHs extend to the margin of the placenta, which is an important diagnostic feature 3
• The size of SCH can be categorized as small, medium, or large based on the volume of blood collection 4
• In later pregnancy (second and third trimesters), SCH may be more difficult to diagnose but remains detectable by ultrasound 5

Risk Factors

• Known risk factors include maternal coagulation factor deficiencies and anticoagulation therapy 5
• Other potential contributing factors include:
  • Abnormal maternal coagulation function 1
  • Autoimmune factors in pregnant women 1
  • Assisted reproductive technologies 1
  • Medication use during pregnancy 1
  • Reproductive tract infections 1

Clinical Significance and Outcomes

• SCH is associated with first trimester vaginal bleeding, which is the most common presenting symptom 4

• The prognosis correlates with:

  • Relative and absolute size of the hematoma (larger hematomas carry worse prognosis) 3
  • Severity of vaginal bleeding 3
  • Changes in hematoma size on follow-up examinations 3
  • Presence of pain 3

• Large SCHs (SCH-III) are associated with significantly higher rates of:

  • First trimester vaginal bleeding 4
  • Early pregnancy loss 4
  • Intrauterine growth restriction (IUGR) 4
  • Placental abruption 4
  • Preterm delivery 4

• Medium-sized SCHs (SCH-II) are associated with increased risk of:

  • Placental abruption 4
  • Early pregnancy loss 4

• Even small SCHs are associated with:

  • Lower gestational age at delivery 4
  • Higher rate of first trimester bleeding 4

Management Considerations

• There are no established clinical treatment guidelines for SCH 1
• No proven treatments exist for SCH, though several investigational therapies have been reported 5
• For larger SCHs in second and third trimesters, consider:
  • Serial growth ultrasounds 5
  • Umbilical artery Doppler studies 5
  • Antenatal fetal testing 5
  • Close monitoring if blood transfusion is required 5

Important Distinctions

• SCH must be differentiated from other placental abnormalities such as:
  • Subamniotic hematomas (which form between chorion and amnion) 6
  • Placental abruption (separation of placenta from uterine wall) 5
  • Gestational trophoblastic disease (which has distinct ultrasound features) 2

Pitfalls in Diagnosis

• Early first trimester SCHs may be confused with normal decidual bleeding 2
• SCH in second and third trimesters can be more difficult to diagnose and manage 5
• SCH must be distinguished from other causes of first trimester bleeding, including ectopic pregnancy and nonviable intrauterine pregnancy 2