Placental abruption

Placental abruption refers to a premature separation of the normally implanted placenta after the 20th week of gestation and before the 3rd stage of labour. It is a potentially fatal complication of pregnancy and is a significant cause of third-trimester bleeding / antepartum haemorrhage.

The estimated incidence is at ~1% of all pregnancies. The rate of placental abruption is thought to have dramatically increased in the past few years.

Patients with a placental abruption typically present with antepartum bleeding, uterine contractions, and fetal distress.

The exact aetiology is unknown, but the final pathophysiology is likely rupture of a spiral artery with haemorrhage into the decidua basalis leading to separation of the placenta. The small vessel disease seen in abruptio placentae may also result in placental infarction.

Risk factors

A number of risk factors have been associated with placental abruption, including:

Location 

According to the position of the abruption within the placenta it can be classified as:

Ultrasound

The sonographic signs of placental abruption include:

  • retroplacental clot (often poorly echogenic) 
  • intraplacental anechoic areas
  • separation and rounding of the placental edge
  • thickening of the placenta: often to over 5.5 cm
  • thickening of the retroplacental myometrium: usually should be 1-2 mm unless there is a focal myometrial contraction
  • disruption in retroplacental circulation
  • intra-amniotic echoes due to intramniotic hemorrhage 
  • blood in the fetal stomach 
  • intermembranous clot in twins

A retroplacental haematoma may be identified only in 2-25% of all abruptions.

The echogenicity of haematomas depend upon their age. Acute haematomas imaged at the time of symptoms tend to be hyperechoic or isoechoic compared to the adjacent placenta. As the haematoma is commonly isoechoic to the placenta, it may be mistaken for focal thickening of the placenta. A 'normal' ultrasound does not exclude a placental abruption-particularly as the blood may have escaped through the vagina in the case of external haemorrhage

In other cases, the retroplacental haematoma may be hypoechoic or of heterogeneous echogenicity.

MRI

MR imaging can accurately detect placental abruption and should be considered after negative US findings in the presence of late pregnancy bleeding if the diagnosis of abruption would change management.

Haemorrhage due to abrution appears as an area of medium to high signal intensity on T1 and high signal intensity on T2 weighted image, located between the placenta and uterine wall.

The larger the size of the abruption, the greater the fetal morbidity. The presence of associated concurrent fetal bradycardia carries a poorer prognosis. Management for small abruptions is usually conservative - serial sonographic examinations with measurement of the retroplacental clot volume, antepartum heart rate and maternal symptoms has been suggested.

The recurrence rate of abruptio placentae is thought to vary between 6-17%.

Complications

A number of conditions can simulate the appearance of placental abruption.

For an isoechoic haematoma in an acute to subacute abruption on ultrasound consider:

For an hypoechoic haematoma on ultrasound consider:

  • uterine leiomyoma
  • poorly echogenic subplacental space:
    • may also simulate a retroplacental haematoma.
    • this appearance is often due to prominent veins in the decidua basalis
    • often colour Doppler sonography may help define the anatomy of this space

Ultrasound - obstetric
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Article Information

rID: 12479
System: Obstetrics
Section: Pathology
Synonyms or Alternate Spellings:
  • Abruptio placentae
  • Abruption of placenta
  • Abruption of the placenta

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