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 ~1% of all pregnancies. The rate of placental abruption is thought to have dramatically increased in the past few years.
A number of risk factors have been associated with placental abruption, including:
- maternal trauma
- age 35 years or older
- cigarette smoking
- cocaine use
- previous placental abruption
- prolonged rupture of membranes
- pre-eclampsia and maternal hypertension: up to 50% of cases
- short umbilical cord
- increased parity
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.
According to the position of the abruption within the placenta it can be classified as:
Ultrasound is almost always the first (and usually the only) imaging modality used to evaluate placental abruption, but an index of suspicion should be maintained for the diagnosis since ultrasound is relatively insensitive for the diagnosis 9. This is partly because a retroplacental haematoma may be identified only in 2-25% of all abruptions.
The sonographic signs of placental abruption include:
- retroplacental haematoma (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 intra-amniotic haemorrhage
- blood in the fetal stomach
- intermembranous clot in twins
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.
Since placental abruption is a concern in a pregnant patient who has undergone traumatic injury, CT is occasionally the first imaging modality used to evaluate the placenta.
The appearance of the placenta in the trauma patient is reviewed at "traumatic abruption placenta scale (TAPS)".
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 abruption appears as an area of medium to high signal intensity on T1 and high signal intensity on a T2 weighted image, located between the placenta and uterine wall.
Treatment and prognosis
Given the low sensitivity for detecting placental abruption on ultrasound, if there is a high clinical suspicion, then it is likely prudent to treat based on the clinical suspicion 9.
If an abruption is detected, then 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%.
- intra-uterine growth restriction (IUGR): particularly when the abruption exceeds 30-40% of the placental area
- fetal demise: with a large unattended abruption
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 a 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 may help define the anatomy of this space
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- placental anatomy
- placental developmental abnormalities
- placenta previa
- spectrum of abnormal placental villous adherence
- abnormalities of cord insertion
- abruptio placentae
- placental pathology
- vascular pathologies of placenta
- placental infections
- placental masses
- molar pregnancy
- twin placenta
Ultrasound - obstetric
- ultrasound (introduction)
- obstetric ultrasound
first trimester and early pregnancy
- gestational sac
- yolk sac
- Beta-hCG levels
- ectopic pregnancy
- multiple gestations
- subchorionic hematoma
- failed early pregnancy
- fetal biometry
- fetal morphology assessment
- fetal echocardiography views
- nonvisualisation of the fetal stomach
- nuchal fold thickness
- absent nasal bone
- choroid plexus cysts
- enlarged cisterna magna
- shortened fetal long bones
- echogenic intracardiac focus (EIF)
- echogenic fetal bowel
- aberrant right sublavian artery
- fetal pyelectasis / fetal renal pelvic dilatation
- single umbilical artery
- sandal gap toes
- Doppler ultrasound
- umbilical artery Doppler assessment
- fetal middle cerebral arterial Doppler assessment
- ductus venosus flow assessment
- umbilical venous flow assessment
- nuchal translucency
- 11-13 weeks antenatal scan
- chorionic villus sampling (CVS) and amniocentesis
- first trimester and early pregnancy