Placenta praevia and low-lying placenta — structured SAQ (15 marks)

(a) Definitions and the measurement (3 marks)

One mark for each definition, one for the measurement technique. No mark for grades I to IV or for marginal, partial or complete — those terms are retired. ^[1][2]

• Placenta praevia: the placenta lies directly over the internal cervical os.^[1]
• Low-lying placenta: the lower placental edge is within 20 mm of the internal os but does not cover it. An edge more than 20 mm away is a normally sited placenta.^[1][2]
• The measurement: transvaginal ultrasound in the sagittal midline plane with an empty maternal bladder and no undue probe pressure, reporting the shortest distance from the lower placental edge to the internal os in millimetres. Transvaginal scanning is safe in praevia because the probe sits in the anterior fornix.^[1][9]
• A mark is available for stating that the uterine isthmus must be distinguished from the cervix, because measuring from the wrong landmark shifts the placenta by a whole classification.^[9]

(b) Further imaging and the accreta signs (4 marks)

One mark for naming accreta spectrum as the concern, two for the ultrasound signs, one for the role and limits of MRI. ^[3][4]

• The concern is placenta accreta spectrum. She has an anterior placenta praevia implanting over two previous caesarean scars, and the risk of accreta with praevia rises with each additional caesarean.^[4][3]
• Grey-scale and colour Doppler signs to seek and report explicitly: ^[3]

• MRI adds value for posterior placentas, for equivocal grey-scale findings and for mapping parametrial or bladder involvement before surgery. It does not outperform good ultrasound for the diagnosis itself and should be reported by someone who does this regularly.^[3][1]
• Report and refer: the finding mandates referral to a centre with a multidisciplinary accreta service.^[1][8]

(c) Antenatal management (4 marks)

One mark each for the admission decision with reasoning, corticosteroids with regimen, haematological optimisation, and the counselling and consent process. ^[5][6]

• Admission versus outpatient care: the Cochrane review of interventions for suspected praevia found only small trials and no convincing advantage for routine hospitalisation, so the decision is individualised. This woman has already bled, has suspected accreta spectrum and is 33 weeks — admission or relocation close to a tertiary unit is justified, and outpatient care would require her to live close by with a companion, immediate transport and clear return instructions.^[6][1]
• Corticosteroids: betamethasone 11.4 mg IM, two doses 24 hours apart, or dexamethasone 6 mg IM for four doses 12 hours apart. A single course reduces perinatal death, respiratory distress syndrome and intraventricular haemorrhage.^[5]
• Haematology: optimise haemoglobin with oral or intravenous iron, keep a valid group and antibody screen, and confirm crossmatched blood availability. Give Rh D immunoglobulin with fetomaternal haemorrhage quantification if she is RhD negative and bleeds.^[1]
• Counselling and consent: the possibility of caesarean hysterectomy, massive transfusion, bladder or ureteric injury and intensive care admission, documented in advance rather than on the day. Discuss cell salvage and involve an interpreter if needed.^[8][1]
• Do not offer cerclage to reduce bleeding — it is not supported outside a trial.^[1][6]

(d) Plan for birth (4 marks)

One mark each for timing with justification, the team and setting, the intraoperative technique, and the haemorrhage ladder. ^[1][8]

• Timing: uncomplicated praevia is delivered at 36+0 to 37+0 weeks; with previous bleeding or suspected accreta spectrum, plan earlier and in a specialist centre, with the exact date set by the multidisciplinary team.^[1][8]
• Team and setting: tertiary unit with an accreta service — senior obstetrician, senior anaesthetist, gynaecological oncologist or pelvic surgeon as local practice dictates, urology available, interventional radiology if used locally, cell salvage, crossmatched blood in the room, critical care bed booked, neonatal team present.^[8][1]
• Intraoperative technique: ultrasound mapping of the placental edge on the table; a uterine incision that avoids transecting the placenta, either above the upper placental edge or a vertical incision; deliver the baby, then make a deliberate decision about whether to attempt placental separation — with accreta spectrum, do not force separation.^[1][8]
• Haemorrhage ladder for the lower segment: uterotonics, tranexamic acid 1 g IV (prophylactic use in praevia is supported by a randomised placebo-controlled phase 3 trial), local haemostatic sutures to the placental bed, intrauterine balloon tamponade, compression sutures, uterine or internal iliac artery ligation, and hysterectomy before she becomes unsalvageable.^[7][8]