Placenta Praevia

Question 1

What is placenta previa?

Answer 1

When the placenta is lying wholly or partly in the lower uterine segment
Complete - placenta covers internal os
Partial - partial coverage
Marginal - placenta extends within 2cm of the cervical os

Question 2

How common is it?

Answer 2

5% have low lying placenta when scanned at 16-20 weeks gestation
Incidence at delivery is only 0.5%, therefore most placentas rise away from the cervix

Question 3

What risk is associated?

Answer 3

Significant haemorrhage by mother and fetus

Question 4

Describe the symptoms and signs

Answer 4

Shock in proportion to visible loss
No pain 
Small bleeds before large
Uterus not tender 
Lie and presentation may be abnormal 
Fetal heart usually normal 
Coagulation problems rare

Question 5

What examination should be avoided?

Answer 5

Digital PV examinations
Speculum exam is safe
Advise against penetrative intercourse

Question 6

What is it associated with?

Answer 6

Caesarean section 
Multiparity
Multiple pregnancy
Having multiple placentas or placenta larger than normal surface area (can happen with twins or triplets) 
Mother >35 years old 
Assisted conception
Fibroids
Endometritis
Maternal smoking

Question 7

Which US type is best for localising the placenta?

Answer 7

TVUS is superior to trans abdominal for localising placenta
If low lying at 20w scan, rescan are 34 weeks
If still present at 34w then scan every 2 weeks

Question 8

What type of delivery does major praevia require?

Answer 8

Caesarian section

Question 9

What type of delivery is done for minor placenta praevia?

Answer 9

Aim for normal delivery unless placenta encroaches within 2 cm of internal os - especially if posterior or thick

Question 10

What is placenta accretia?

Answer 10

Abnormal adherence of all or part of the placenta to the uterus
Termed placental increta if myometrium infiltrated

Question 11

What is placental percreta?

Answer 11

Placental penetration reaches the serosa

Question 12

Where should the placenta implant normally?

Answer 12

The upper uterus

Question 13

What causes placenta praevia?

Answer 13

Unclear
Hypothesis: placenta implants lower down when the upper uterus endometrium not well vascularised - may be due to damage from previous Caesarian section, abortion, uterine surgery, multiparity (can all decrease vascularisation)

Question 14

Why does bleeding occur?

Answer 14

As the lower uterine segment grows, it disrupts placental vessels causing bleeding - usually bright red and sudden onset

Question 15

When does the bleeding typically occur?

Answer 15

After 20 weeks gestation

Question 16

Can the amount of bleeding vary?

Answer 16

Yes and can be intermittent or continuous

Can increase during labour due to contractions and cervical dilatation

Question 17

What complications can occur?

Answer 17

Maternal - related to blood loss

Fetal - hypoxia and pre term delivery

Question 18

How is placenta praevia diagnosed?

Answer 18

Prenatal USS

Sometimes during labour

Question 19

How is placenta praevia managed?

Answer 19

Plan for and prevent pre term birth 
Corticosteroids 
Minor bleeding - bed rest and monitoring
Major bleeding - blood products and fluids 
In severe cases: immediate CS

Question 20

How should the bleeding be managed?

Answer 20

Admit
Treat shock
Cross match blood
Final USS at 36-37w to determine method of delivery

Question 21

Why is there a predisposition to PPH?

Answer 21

Due to poor lower segment contractility