Placental abruption

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

Epidemiology

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

Clinical presentation

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

Pathology

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.

Associations and riskRisk factors

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

• maternal trauma
• maternal age of 35 years or older
• maternal cigarette smoking
• maternal cocaine use
• thrombophilia
• previous placental abruption
• chorioamnionitis
• prolonged rupture of membranes
• pre-eclampsia and maternal hypertension: often seen in as many as 50% of cases
• short umbilical cord
• increased parity

Location 

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

• marginal placental abruption: commonestmost common by far
• retro-placental abruption 
• pre-placental abruption 

Radiographic features

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 1/2.5 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 clot

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 iso-echoic 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 hypo-echoic 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.

Complications

• intra-uterine growth restriction (IUGR) : particually when the abruption exceeds 30-40% of the placetal area
• fetal demise : with a large unattended abruption

Treatment and prognosis

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.

The recurrence rate of abruptio placentae is thought to vary between ~66-17%.

Differential diagnosis

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

For an iso-echoic haematoma in an acute to sub-acute abruption on ultrasound consider:

• causes of placentomegaly
• a focal myometrial contraction: transient

For an hypo-echoic 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 color Doppler sonography may help define the anatomy of this space

See also

• peri-gestational haemorrhage
• sub-chorionic haemorrhage