Placenta praevia Flashcards
Define placenta praevia vs low-lying placenta.
Definitions apply after 16 weeks
Placenta praevia = placenta lies directly over the internal os
Low-lying placenta = placental edge lies <2 cm from the internal os
How common is placenta praevia at different gestations?
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 cervix
What are the risk factors for placenta praevia?
- multiparity
- multiple pregnancy
- cesarean section - embryos are more likely to implant on a lower segment scar from previous caesarean section; % risk increases linearly after each previous C/S
- uterine structural anomaly
- assisted conception
What are the clinical features of placenta praevia?
- 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
What are the grades of placenta praevia?
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
How do you diagnose placenta praevia?
Picked up on routine 20 week abdominal USS (i.e. anomaly scan) - RCOG recommend TVUSS to improve accuacy of placental localisation
But may also present with painless vaginal bleeding in the second or third trimester.
Which type of examination should not be performed in placenta praevia?
Digital vaginal examination should not be performed on women with active vaginal bleeding until the position of the placenta is known with certainty.
It can cause haemorrhage if disrupted.
What % of placentas move away from the os by 36 weeks?
90%
What are the causes of bleeding in placenta praevia?
May occur spontaneously
From placental trauma e.g., sexual intercourse, vaginal examination
As cervix opens at the onset of labour - as the presenting part moves into the lower segment, the placenta may be torn or may separate (abrupt) from the uterus, in whole or in part. Massive haemorrhage results from both the mother and the fetus. Untreated, this almost always results in the death of the mother and fetus
Treatment for PP should be thought of in three dimensions.
- Degree of bleeding: none, mild to moderate, severe.
- Labour: no, yes.
- Duration of pregnancy: first trimester, second trimester but not viable, viable but not term, term (age of viability varies depending on local resources).
What is the management of asymptomatic low-lying placenta or placenta praevia?
- Pelvic rest (e.g. avoid penetrative sex, no douching) and seek medical attention in case of bleeding beyond spotting
-
Rescan at 28-32 weeks gestation (only 10% go on to have a low-lying placenta later in pregnancy, many migrate up)
- If still low-lying/praevia at 32 weeks → rescan at 36 weeks
- If still low-lying/praevia at 36 weeks → recommend elective C-section at 36-37 weeks gestation (i.e. before allowing for spontaneous labour to occur)
- +/- Colour flow Doppler imaging/MRI if suspecting abnormally adherent placenta (accreta)
At how many weeks is elective C-section done in placenta praevia?
36-37 weeks (according to guidelines)
Should anti-D be considered in placenta praevia?
Usually standard protocols are followed where anti-D is given at 28 weeks but if there is a potential event with placental trauma e.g. placenta praevia with bleeding, then consider additional anti-D within 72 hours of the bleeding starting.
What is the management of syptomatic placenta praevia if the mother is haemodynamically stable with no evidence of fetal distress?
ABCDE approach:
- Gain IV access
- Bloods (FBC, Rhesus status, cross-match, clotting screen)
- Continuous foetal monitoring
- Give anti-D immunoglobulin in Rh-negative women
AND:
- Admit + give steroids - until bleeding has stopped and for further 48 hours for observation
-
Rescan at 36 weeks
- If still low-lying/praevia -> elective C-section at 34-36 weeks
How do you counsel a patient with symptomatic placenta praevia?
Admit until bleeding has stopped and for a further 48 hours
Explain the importance of the finding and that the foetus needs to be monitored
Explain that prompt delivery needs to be discussed (based on gestation)
Explain the risks of delivery:
- Major blood loss
- May require a blood transfusion
- May require a hysterectomy
