Disorders of Placenta

Question 1

What is oligohydramnios?

Answer 1

Reduced amniotic fluid

Less than 500ml at 32-36 weeks and an amniotic fluid index (AFI) < 5th percentile.

Question 2

What are causes of oligohydramnios?

Answer 2

premature rupture of membranes
Potter sequence: bilateral renal agenesis + pulmonary hypoplasia
intrauterine growth restriction
post-term gestation
pre-eclampsia

Question 3

What is placenta accreta?

Answer 3

the attachment of the placenta to the myometrium, due to a defective decidua basalis

Question 4

What is the risk of placenta accreta?

Answer 4

As the placenta does not properly separate during labour there is a risk of postpartum haemorrhage.

Question 5

What are RFs of placenta accreta?

Answer 5

previous caesarean section
placenta praevia

Question 6

What are the 3 types of placenta accreta?

Answer 6

accreta: chorionic villi attach to the myometrium, rather than being restricted within the decidua basalis

increta: chorionic villi invade into the myometrium

percreta: chorionic villi invade through the perimetrium

Question 7

What is placenta praevia?

Answer 7

a placenta lying wholly or partly in the lower uterine segment

Question 8

What is the epidemiology of placenta praevia?

Answer 8

5% will 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 9

What are associated factors of placenta praevia?

Answer 9

multiparity
multiple pregnancy
embryos are more likely to implant on a lower segment scar from previous caesarean section

Question 10

What are clinic features of placenta praevia?

Answer 10

shock in proportion to visible loss
no pain
uterus not tender
lie and presentation may be abnormal
fetal heart usually normal
coagulation problems rare
small bleeds before large

Question 11

How is placenta praevia diagnosed?

Answer 11

digital vaginal examination should not be performed before an ultrasound as it may provoke a severe haemorrhage

placenta praevia is often picked up on the routine 20 week abdominal ultrasound

the RCOG recommend the use of transvaginal ultrasound as it improves the accuracy of placental localisation and is considered safe

Question 12

How is placenta praevia defined and graded?

Answer 12

I - placenta reaches lower segment but not the internal os
II - placenta reaches internal os but doesn’t cover it
III - placenta covers the internal os before dilation but not when dilated
IV (‘major’) - placenta completely covers the internal os

Question 13

If placenta praevia is found at the 20 weeks scan, what are the next steps?

Answer 13

rescan at 32 weeks
no need to limit activity or intercourse unless they bleed
if still present at 32 weeks and grade I/II then scan every 2 weeks
final ultrasound at 36-37 weeks to determine the method of delivery

Question 14

If placenta praevia still present at 36-37 weeks, what is the mode of delivery?

Answer 14

elective caesarean section for grades III/IV between 37-38 weeks
if grade I then a trial of vaginal delivery may be offered

Question 15

What is done if woman with placenta praevia goes into labour before C-section?

Answer 15

an emergency caesarean section should be performed due to the risk of post-partum haemorrhage

Question 16

What is done if woman with placenta praevia presents with bleeding?

Answer 16

admit
ABC approach to stabilise the woman
if not able to stabilise → emergency caesarean section
if in labour or term reached → emergency caesarean section

Question 17

What is the prognosis of placenta praevia?

Answer 17

death is now extremely rare
major cause of death in women with placenta praevia is now PPH