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Definition vasa praevia

Fetal vessel running in the free placental membranes within 2 cm of the cervix

Unprotected by placental tissue or Wharton’s jelly of the umbilical cord, a vasa praevia is likely to rupture in active labour, SROM or cervical dilation.


Fetal outcomes

AMOSS study (2017) found no perinatal mortality when diagnosed prenatally.
40% perinatal mortality if undiagnosed.

Over 50% undiagnosed cases will require urgent neonatal transfusion of O negative blood due to fetal exsanguination from relatively small volumes of blood.



1:2500 to 1:5000



Painless APH
Small volumes of blood but quickly leads to fetal distress


What is the guidance around screening for vasa praevia

- Currently no evidence for cost-benefit of routine screening; targeted screening has good cost-benefit analysis.
- Mid-trimester scan - placental location and cord insertion should be assessed transabdominally.
- If risk factors identified, TV USS with associated colour doppler should be used to screen for vasa praevia.

NB. over half of vasa praevia associated with velamentous cord insertion. Incidence of velamentous cord insertion is 1%. Routine Mid-trimester US screening has NPV and PPV approaching 100%.


Risk factors for vasa praevia

placenta praevia or LLP*
velamentous cord insertion*
bilobed placenta
succenturiate placental lobes
conception by ART
Multiple pregnancy


Management for vasa praevia

Consider admission after 30/40

Elective caesarean delivery at 34-35/40

Give antenatal steroids due to likelihood of preterm delivery

If in early labour/PPROM- cat 1 CS

2 weekly growth scans

Pre-operatively - TVUSS to map fetal vessels to try not to inadvertently lacerate during CS

Inform neonatal team - to prepare for neonatal resuscitation, prepare for blood transfusion


What are the criteria for ultrasound diagnosis?

- Visualising aberrant linear or tubular echolucent structures with 2D imaging

- Demonstrating blood flow in these structures using colour or power doppler

- Demonstrating umbilical artery/venous doppler waveforms using pulse wave doppler

- Aberrant vessels located over or within 2cm of internal os as attached to the inner perimeter of fetal membranes


A 23 year old primigravida has just had a fetal morphology scan performed at 20 weeks. The report stated that the placenta was posterior, low lying and that vessels were observed at the internal os. The fetus is otherwise well.

a) List the differential diagnoses. (2 marks)

• Vasa praevia - type 1 or 2
• Cord presentation
• Marginal placental sinuses in placenta praevia


If mid trimester scan noted vessels close to the internal os.
b) Discuss what you would advise the patient at this stage. (4 marks)

• Needs TVUSS with colour Doppler by experienced monographer and radiologist to confirm diagnosis
• Needs repeat TVS at 30-32 weeks as small chance vessels may move out the way (15%)
• If vasa praevia confirmed – significant risk to fetus if SROM/PTB/bleed – exsanguination and death
• Suggest elective admission from 30 weeks until delivery
• Recommend antenatal steroids from 30 weeks
• If managed as an outpatient - do not travel far from hospital, keep phone handy and stay with others, If bleeding/SROM/pain occurs in community – call ambulance and avoid intercourse
• Aim for elective delivery between 34-35/40


c) She presents at 32 weeks with painful contractions but no bleeding. What is your management plan? (9 marks)

• Setting – manage in 3’ centre with NICU and blood bank available – transfer only if stable if necessary
• Get help- senior obs/anaesthetics/midwifery. OT/NICU.
• IVL, G&S, X-match, FBC
• NBM until stable
• CTG – if fetal distress Cat 1 CS, if no fetal distress, as below
• Further history
- strength/freq of contractions – increasing or decreasing?
- ROM?
- Abdo pain between contractions?
- FM’s
- PMHx, surgical, meds, allergy
• Examination
- Palpate contractions
- Speculum to assess cervical dilation – high risk bleed if dilating +/- fFN
- USS + colour doppler if time to check for persistence of vasa praevia and identify vessels pre-op
• Antenatal corticosteroids - potential for spontaneous or iatrogenic PTB
• Tocolysis until steroids complete
• If stabilized – keep for observation until delivery
• If fetal compromise, ongoing contractions or SROM then high risk bleeding – consider delivery by CS with blood available for baby
• Paeds at delivery – if SROM/bleed then the bleeding is fetal – prepare for immediate transfusion


You arrange admission to hospital for a 34 year old multiparous woman, at 30 weeks gestation with an antenatally diagnosed Type 1 vasa praevia. This was diagnosed at her routine morphology scan at 19 weeks gestation. She has had no bleeding this pregnancy and her previous pregnancy resulted in a normal term delivery. With respect to her antenatally diagnosed vasa praevia:

(i) Describe the two (2) features that would have been visualized at her routine morphology scan that alerted the sonographer to the increased risk of a Type 1 vasa praevia, and enabled further investigation. (2 marks)

- placenta praevia
- velamentous cord insertion


(ii) Outline the details that you would expect to see on the morphology scan report that would reassure you of an accurate diagnosis of vasa praevia. (4 marks)

The scan was performed by a qualified sonographer and read by a radiologist with experience in reporting placental abnormalities

Both TA and TV scans were performed- TV scans are more accurate for diagnosis of vasa praevia

Colour doppler used to show arterial and venous flow

Careful documentation of the placental location with regards to the os

Careful documentation of any accessory lobes, their relationship to the main body of the placenta, and the documentation of the location fetal vessels

Documentation that the umbilical cord is not in the area of the cervix and thus not what is being seen on USS (cord presentation)

Diagnostic criteria for VP
- Visualising aberrant lineral or tubular echolucent structures with 2D imaging within 2cm of os
- Demonstrating blood flow in these structures using colour or power Doppler
- Demonstrating umbilical arteria/venous doppler waveforms using a pulse wave Doppler
- Aberrant vessels located over or within 2cm of the internal os attached to the inner perimeter of the fetal membranes


iii) Identify two (2) significant benefits of antenatal detection of vasa praevia for this pregnancy. (2 marks)
Justify her admission to hospital. (2 marks)

Benefits of antenatal detection
Antenatal surveillance: vasa praevia can be associated with other placental abnormalities and there is a risk of growth restriction with velamentous cord insertion- regular USS can be performed to monitor for growth restriction

Planning for delivery: the mode of delivery needs to be by lower-segment Caesarean section and this may need to be an emergency procedure if there is any bleeding
Significant reduction in perinatal mortality and morbidity
Overall perinatal mortality is 36%, compared with 97% survival with prenatal diagnosis

Justify admission to hospital
There is an increased risk of tearing of the fragile vessels as the uterus grows and the lower segment stretches in the third trimester
If there is tearing of the vessels and an APH, then a Caesarean section will need to be performed immediately as the baby may exsanguinate and die
If she is in hospital then this can be performed much faster than if she were at home and had to call an ambulance to come in
Allows immediate access to neonatal care and transfusion


Outline your management plan following admission for vasa praevia at 30 weeks. (5 marks)

Valid group and hold and IVL at all times, in case of need for emergency LSCS
Explain procedure for emergency LSCS and sign consent to ensure that this is completed in cause of emergency
Regular growth scans- every 2 weeks from 34 weeks to monitor for growth restriction
Vessel mapping can also be done to attempt to avoid inadvertent injury to fetal vessels at LSCS
Evaluate if vasa praevia has moved out of the way
Scheduling of planned CS between 34-35 weeks with aim to avoid labour prior to LSCS
Daily CTG monitoring
Encourage woman to mobilise and give her compression stockings to wear to reduce her risk of VTE due to immobility
Education of the woman that she should call for review immediately should she have any bleeding, ROM, signs of labour or concern about her baby's movements
Immediate CTG and prepare for delivery if any of these occur
Administration of corticosteroids for fetal lung maturation in anticipation of potential preterm delivery
Ensure the hospital has paediatric expertise and an appropriate level of neonatal care


Define type 1 and type 2 vasa praevia.

Type I - velamentous insertion of the umbilical cord into the placenta

Type II - velamentous fetal vessels connecting the placenta to a succenturiate placental lobe