What is Placenta Praevia?

Placenta praevia occurs when the placenta is situated wholly or in part into the lower segment of the uterus and is located close to the opening of the cervix. Clinically this is important as it can give rise to bleeding either during pregnancy, during labour or following delivery.


Placenta praevia complicates approximately 1 in 200 pregnancies. The incidence has increased over time due to the rising incidence of caesarean section, which is a risk factor, and improved diagnostics. While abruption can occur in women with no risk factors, there are factors, listed below, that increase the risk of a mother experiencing placental abruption.

Risk Factors

The cause of placenta praevia remains unknown, however risk factors include:

Placenta praeviaThe increased risk of placenta praevia following caesarean section is highest for the pregnancy immediately following the caesarean and decreases in subsequent pregnancies.


The lower uterine segment only develops fully in the third trimester. This means that prior to the third trimester many placentas may appear to be located close to the cervix and are termed low lying placentas. However, as the pregnancy progresses and the lower segment develops fully, a large number (>90%) of low lying placentas detected in early pregnancy move away from the cervical opening.


Classically patients present with an unprovoked, painless episode of vaginal bleeding. The amount of vaginal blood loss varies between minor to massive haemorrhage. Blood loss is most frequently intermittent with unpredictable recurrence.

Following an episode of bleeding, it is most likely that you will need to stay in hospital for a period of time so that both you and your baby can be monitored closely.

Clinical Examination

Placenta praevia examinationOn examination, your doctor will be examining you for signs and symptoms of placental praevia as well as other differential diagnoses depending on your presenting symptoms. They will be especially concerned with your vital signs, including heart rate and blood pressure to assess whether you are showing any signs of shock.

Other than your health, they will also be concerned with the health of your unborn child. They will be interested in if your baby is moving, its heart rate and how many weeks gestation your baby is. If there are any signs of foetal compromise, active bleeding, uterine activity or tenderness a cardiotocograph (CTG) will be applied for continuous monitoring.

Several blood tests will be ordered and an ultrasound may be necessary.

How is it Diagnosed

Placenta praevia is diagnosed using ultrasound. The most accurate method for diagnosing placenta praevia is by trans-vaginal ultrasound. This involves the insertion of the ultrasound probe into the vagina. Ultrasound using a probe over the abdomen (trans-abdominal) can be performed, however, this method is more likely to incorrectly identify cases of placenta praevia compared to trans-vaginal ultrasound.


UltrasoundIf your placenta was determined as low lying from an ultrasound scan performed prior to the third trimester of pregnancy, it is most likely that as the lower segment of the uterus develops fully that your placenta will move away from the opening of the cervix.

For those women in which this does not occur, placenta praevia can be responsible for bleeding from the vagina either during pregnancy, during labour or following labour. This may result in anaemia, hysterectomy, a blood transfusion and/or possible infection. In the Western world, placenta praevia is a rare cause of maternal mortality, approximately 0.03%.

Foetal death is slightly higher than maternal mortality, approximately 4-8%, and is associated with pre-term birth (50%) and intrauterine growth restriction. While the cause is unknown, the risk of birth defects in the foetus are doubled.


Placenta praevia managementManagement is dependant on several factors including maternal and foetal wellbeing, volume of blood loss, degree of placenta praevia and gestational age.

If the bleeding becomes life threatening, resuscitation and stabilisation of the mother is the primary focus followed by delivery of the baby by emergency caesarean section.

In cases where the foetus is pre-term and the bleeding is minimal, the goal is to delay the delivery to allow for maturation of the foetus without increasing the risk to the mother. In most cases this will involve admission to hospital where you and your baby can be monitored closely. Unless there is spontaneous labour of heavy sustained bleeding necessitating emergency caesarean delivery, delivery is by planned caesarean section at 37-38 weeks gestation.


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