A 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 over last few decades (valid at the time of initial writing).
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.
Associations and risk 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
- previous placental abruption
- prolonged rupture of membranes
- pre-eclampsia and maternal hypertension : often seen in as many as 50% of cases
- short umbilical cord
- increased parity
According to the position of the abruption within the placenta is can be classified as a
- marginal placental abruption : commonest by far
- retro-placental abruption :
- pre-placental abruption :
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 cm
- thickening of the retroplacental myometrium : usually should be 1 - 2 mm unless there is a focal myometrial contraction
- intra-amniotic clot
A retroplacental haematoma may be identified only in 2 - 25% of all abruptions.
The echogenicity of haematomas will 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.
- 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 ~ 6 - 17 %.
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
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
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Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|
|Abruption of placenta||✗|
|Abruption of the placenta||✗|