Placenta Praevia

Question 1

A 26-year-old female is being seen in the obstetric clinic. Her 20-week
anomaly scan showed placenta praevia.

What is the definition of placenta praevia?

Answer 1

• In 2014, the American Institute of Ultrasound in Medicine recommended a change in the definition to “a condition where the placenta lies directly over the maternal os on a transabdominal or transvaginal ultrasound scan”.

Question 2

What is the definition of a “low lying placenta”?

Answer 2

• A low lying placenta is defined as a placenta whose lowest edge lies within 20 mm of the os, after 16 weeks of pregnancy.

Question 3

What is the incidence of placenta praevia?

Answer 3

• 1 in 200 pregnancies (but this varies with the definition).
• The incidence is increasing in association with the increasing number
  of caesarean sections and increased assisted reproductions.

Question 4

What are the risk factors for the development of placenta praevia?

Answer 4

• Previous caesarean section(s).
• Assisted reproduction.
• Increased maternal age.
• Previous placenta praevia.
• Maternal smoker.

Question 5

You are asked to review the patient. She identifies as a Jehovah’s Witness.

What are the key points that you want to discuss with her?

Answer 5

• Ideally, this patient should be reviewed by a consultant anaesthetist in a quiet room, with no other friends or family members present.
• Establish what the patient knows about her condition and the risks associated with placenta praevia including major haemorrhage, hysterectomy and death.
• Establish the patient’s wishes with respect to treatment in hospital, focusing on the exact blood products she would and would not accept, to include the use of tranexamic acid and cell salvage.
• Ensure documentation of the exact wishes of the patient in her notes and in an Advanced Directive that is signed and witnessed.

Question 6

The patient is booked in for an elective caesarean section at 38weeks of gestation. What can be done to pre-optimise her prior to surgery?

Answer 6

• Regular full blood count and haematinics to allow for enteral or intravenous iron preoperatively if required.
• Consider the use of erythropoietin preoperatively.
• Document the plan for pregnancy and delivery including surgical
  intervention, to include:
• Site of delivery.
• Confirming the patient’s wishes at the time of delivery/bleeding.
• Ensuring a senior obstetric and anaesthetic team.
• Early use of multi-modal uterotonic agents.
• Early consideration of interventional procedures in the case of major obstetric haemorrhage.
• Early use of anti fibrinolytic agents.
• Checking the availability of cell salvage and any blood products that are acceptable to the patient.
• High dependency or intensive care unit postoperatively.

Question 7

How does cell salvage work?

Answer 7

• Blood is harvested from the surgical field using a large bore, low-pressure suction cannula.
• Amniotic fluid can be collected using a separate suction system.
• The blood is anticoagulated to prevent clotting. This is usually achieved with heparin solutions but ACD-A (anticoagulant citrate dextrose) solutions can also be used.
• If enough blood is collected, it is centrifuged, washed and re-suspended
  in saline before being transfused back into the patient.

Question 8

What are the concerns with the use of cell salvage in obstetric patients?

Answer 8

• There were previously concerns associated with the risk of amniotic fluid embolism in the use of cell salvage in obstetric patients.
• Some centres advocate the use of leukocyte depletion filters, but it is thought that the usual filtration process is effective in removing amniotic fluid cells from the collected blood.
• Foetal red cells are not distinguished from maternal red cells, so there is a risk of alloimmunisation and anti-D is likely to be required for Rhesus negative mothers with a Rhesus positive foetus. Local guidelines should be adhered to.