Suspected pulmonary embolism in late pregnancy — structured SAQ (15 marks)

(a) Working diagnosis, immediate management, and imaging (4 marks)

One mark for the diagnosis, one for the immediate management, two for the imaging choice and reasoning. ^[1][2]

• Working diagnosis: pulmonary embolism complicating a hypercoagulable late pregnancy in a high-risk woman. The risk factors (BMI 38, prior operative delivery, family history, late pregnancy) and the clinical presentation (sudden dyspnoea, pleuritic chest pain, haemoptysis, tachycardia, hypoxaemia, loud P2) all support the diagnosis.^[1]
• Immediate management: high-flow oxygen to maintain saturations above 95 per cent, intravenous access, bloods including coagulation, troponin and group and save, ECG, left lateral tilt to relieve aortocaval compression, and initiate therapeutic low-molecular-weight heparin immediately while awaiting imaging. The patient is haemodynamically stable but is at high risk of decompensation.^[1]
• Diagnostic imaging: ventilation-perfusion scanning is the preferred first-line modality because the chest X-ray is normal. The advantage over CT pulmonary angiography is the lower maternal breast radiation dose, which reduces the lifetime risk of radiation-induced breast cancer. The fetal radiation dose from V/Q scanning is slightly higher than from CTPA but both are well below the threshold of harm.^[2][4]
• The d-dimer of 1800 ng/mL is not diagnostic of VTE — it is raised throughout pregnancy and most women with a raised d-dimer do not have a clot. The role of the d-dimer is to exclude VTE at low pretest probability; at higher pretest probability, imaging is required regardless of the d-dimer value.^[4]

(b) Anticoagulation strategy (4 marks)

One mark each for the agent and dose, the route, the monitoring, and the duration. ^[1]

• Agent and dose: enoxaparin 1 mg per kilogram subcutaneously twice daily, or 1.5 mg per kilogram once daily. For a 90 kg woman, the twice-daily dose is 90 mg subcutaneously twice daily. Alternatives: dalteparin 200 IU per kilogram once daily, tinzaparin 175 IU per kilogram once daily.^[1]
• Route: subcutaneous injection. Self-administered at home once the woman is established on therapy and counselled.^[1]
• Monitoring: anti-Xa level monitoring is recommended in late pregnancy, in women with a BMI over 40, in renal impairment, or at high bleeding risk. Target peak anti-Xa 0.5 to 1.0 units per millilitre for twice-daily dosing, taken 4 hours after the dose.^[1]
• Duration: for acute VTE in pregnancy, 3 to 6 months or at least 6 weeks postpartum, whichever is longer. In this case, the woman is at 34 weeks gestation, so treatment continues until at least 6 weeks postpartum, with a transition to oral warfarin from day 2 to 5 postpartum if she prefers.^[1]

(c) Peripartum management plan (4 marks)

One mark each for the anticoagulation transition, the timing, the anaesthetic plan, and the mode of delivery. ^[1][3]

• Anticoagulation transition: stop enoxaparin 24 hours before the planned induction. Switch to intravenous unfractionated heparin, which can be stopped 4 to 6 hours before anticipated delivery and 4 to 6 hours before neuraxial insertion. Restart unfractionated heparin 4 to 6 hours after delivery if there is no bleeding, then transition back to LMWH.^[1]
• Timing: planned induction of labour at 39 weeks, individualised if complications arise. The PE itself is not an indication for early delivery unless the woman is haemodynamically unstable.^[1]
• Anaesthetic plan: early neuraxial analgesia with a slow epidural top-up is preferred for labour, provided the anticoagulation has been correctly transitioned. The timing with the last LMWH or unfractionated heparin dose is critical to minimise the risk of epidural haematoma. General anaesthesia for caesarean if neuraxial is contraindicated.^[1][5]
• Mode of delivery: vaginal delivery is preferred unless there is an obstetric indication for caesarean. The PE itself does not mandate caesarean. A short second stage with assisted delivery reduces the Valsalva-related cardiac output spike.^[1]

(d) Postpartum prophylaxis and long-term follow-up (3 marks)

One mark each for the postpartum prophylaxis, contraception, and follow-up. ^[1][3]

• Postpartum prophylaxis: continue therapeutic LMWH for at least 6 weeks postpartum, with transition to warfarin from day 2 to 5 if preferred. The woman is high risk under the RCOG Green-top 37a framework (acute VTE in pregnancy) and warrants 6 weeks of postpartum prophylaxis at therapeutic dose for the index event, with consideration of extended prophylaxis if additional high-risk features emerge.^[1][3]
• Contraception: progesterone-only options are preferred — progesterone-only pill, depo medroxyprogesterone, etonogestrel implant, or levonorgestrel intrauterine system. Combined oral contraception is contraindicated because of the elevated VTE risk. Counsel before discharge.^[1]
• Long-term follow-up: surveillance for post-thrombotic syndrome, recurrence risk counselling for future pregnancies (the woman would require antenatal prophylactic LMWH in any future pregnancy), thrombophilia testing guided by the personal and family history, and preconception counselling for the next pregnancy.^[1][6]