Vasa praevia — structured SAQ (15 marks)

(a) Explaining the diagnosis and its significance (3 marks)

One mark each, maximum three. Marks for the mechanism, the risk, and a quoted outcome figure. ^[2][1]

• The mechanism, in plain terms: one of the baby's blood vessels is running through the membranes across the opening of the cervix, without the protection of the cord jelly or the placenta. If the membranes break, that vessel can tear; if the baby's head presses on it, it can be squeezed shut.^[1][4]
• Why it is dangerous: the blood lost is the baby's, not hers, so she can feel completely well while the baby exsanguinates. Fetoplacental blood volume is small — direct measurement gives about 93 mL/kg at 31 weeks — so a loss of only 100 to 200 mL can be fatal.^[10][2]
• The outcome data to quote: in the multicentre series of 155 pregnancies, survival was 97% when vasa praevia was diagnosed antenatally versus 44% when it was not, and in the Australian population-based study there were no perinatal deaths among 58 antenatally diagnosed women, while case fatality was 40% among the 5 not diagnosed. Her diagnosis is the single most important thing that has happened in this pregnancy.^[2][3]

(b) Antenatal management plan and the admission decision (4 marks)

One mark each, maximum four. ^[4][7]

• Confirm and document the vessel map — type, course, relation to the os, and place a clear plan in her record that any clinician meeting her at 03:00 can follow. State explicitly: no digital vaginal examination and no amniotomy.^[1][4]
• Antenatal corticosteroids timed to the planned birth date, a neonatal cot booked, and the neonatal team informed of the diagnosis in advance.^[1][6]
• Admission decision, justified rather than asserted. The international consensus states that outpatient management of an asymptomatic patient without risk factors for preterm birth is reasonable, and the panel reached no agreement on routine hospitalisation. Set out what would change your mind: any bleeding, contractions, a short cervix, twins, or a long distance from a unit with 24-hour immediate caesarean capability. State a gestation at which you would review admission — commonly around 30 to 34 weeks.^[4][7]
• Counsel and safety-net specifically: any bleeding, any contractions, or rupture of membranes means calling an ambulance and coming straight to the tertiary unit, not the local hospital. Discuss relocation if she lives remotely.^[1][7]

A mark is available for citing the mortality argument for admission: in the systematic review of deaths despite prenatal diagnosis, every perinatal death occurred with an unscheduled delivery, and a routine hospitalisation policy was associated with less neonatal transfusion (0.9% versus 6.0%). ^[7]

(c) Timing and mode of birth, with the evidence (3 marks)

One mark for mode with justification, two for timing with evidence. ^[5][6]

• Mode: planned caesarean section, before labour and before the membranes rupture. There is no vaginal-birth pathway for confirmed vasa praevia. Place the uterine incision to avoid the mapped vessels, and have the neonatal team present.^[1][4]
• Timing: a planned birth in the mid-thirties. The international consensus supports scheduled caesarean between 35 and 37 weeks for asymptomatic patients.^[4]
• The two datasets to reconcile: the Robinson and Grobman decision analysis found 34 weeks optimal, with sensitivity analyses keeping the optimum at 34 to 35 weeks and no benefit from amniocentesis for lung maturity. The later meta-analysis of 490 neonates found complications fell steadily to 36 weeks — perinatal death 0%, respiratory distress 5.3%, neonatal transfusion 2.9% — concluding that prolonging to 36 weeks is safe and beneficial in uncomplicated antenatally diagnosed cases.^[5][6]

Full marks for a candidate who states a specific plan (for example "scheduled caesarean at 35 to 36 weeks after corticosteroids") and can defend both the earlier and later evidence. ^[5][6]

(d) Immediate management of ruptured vasa praevia (5 marks)

One mark each, maximum five. The pattern of marks rewards speed and the neonatal half of the answer. ^[1][8]

• Recognise and declare. "This is a ruptured vasa praevia with fetal exsanguination." Fresh bleeding, acute fetal bradycardia and completely normal maternal observations are the diagnostic triad. Declare a category-1 caesarean immediately.^[1][2]
• Do not delay for tests. No Apt test, no Kleihauer, no ultrasound. The interval from rupture to birth is what determines survival.^[1][2]
• Call the neonatal team and use the words "acute fetal blood loss" so they attend with volume and arrange emergency group O RhD-negative red cells to the operating theatre.^[8][9]
• Theatre and anaesthesia. Transfer immediately; general anaesthesia is usual because regional block is too slow. Maternal intravenous access and bloods as for any caesarean, but she is not the bleeding patient.^[1][4]
• Neonatal resuscitation: ventilation plus volume. Effective positive-pressure ventilation first, then intravascular access, adrenaline and volume expansion if the response is inadequate. Give a 10 mL/kg bolus of isotonic saline or red cells over about 5 minutes, repeated according to response, with early umbilical venous access. In suspected hypovolaemic arrest, current guidance sequences intravenous adrenaline before the volume bolus. Recheck the haemoglobin — a normal first value does not exclude major acute loss.^[8][9]

Also creditable: send the placenta and membranes for histopathology to confirm the diagnosis, document times, and debrief the woman and her partner. ^[1][3]