Venous Thromboembolism in Pregnancy

Venous thromboembolism in pregnancy is the formation of clot in deep veins (deep vein thrombosis) with or without migration to the lungs (pulmonary embolism). Pregnancy raises risk through hypercoagulability, venous stasis and vessel injury, and risk is highest in the postpartum weeks. It is an important cause of maternal death and needs prompt anticoagulation.

• Risk factors: previous thrombosis, thrombophilia, age above 35 years, body mass index above 30 kg/m2, caesarean section, immobility, preeclampsia, infection, assisted conception, sickle cell disease, nephrotic syndrome.
• Most deep vein thrombosis occurs in the left leg.
• Anticoagulation continues for at least 6 weeks after delivery and 3 months in total.

Leg swelling, pain and warmth, or breathlessness, pleuritic chest pain, cough and haemoptysis, sometimes with collapse. Compare calf circumference 10 cm below the tibial tuberosity.

• Difference in calf circumference of 2 cm or more.
• Pulse above 100 per minute and respiratory rate above 20 per minute suggest embolism.
• Differential diagnosis: cellulitis, superficial thrombophlebitis, muscle strain, ruptured Baker cyst, pneumonia, pleurisy, peripartum cardiomyopathy, normal pregnancy oedema.
• Complications: pulmonary embolism, post thrombotic syndrome, recurrence, bleeding on anticoagulation, heparin induced thrombocytopenia, maternal death.

The approach is clinical probability with compression ultrasound and, if needed, lung imaging.

• Compression ultrasound of the leg veins; repeat at 3 and 7 days if negative and suspicion remains.
• For suspected pulmonary embolism: oxygen saturation, ECG, chest X-ray with shielding, then CT pulmonary angiography or ventilation perfusion scan.
• D-dimer rises in normal pregnancy and is not reliable.
• Baseline full blood count, creatinine, liver enzymes, coagulation screen and weight before heparin.

The principle is immediate therapeutic low molecular weight heparin, continued through pregnancy and for 6 weeks after delivery.

• Supportive: elevate the leg; walk once anticoagulated; graduated compression stockings of 20 to 30 mmHg for symptoms; oral fluids; stop smoking.
• Pharmacological: enoxaparin 1 mg/kg subcutaneous 12-hourly (booking weight) for the rest of pregnancy and 6 weeks postpartum, at least 3 months in total; unfractionated heparin 80 units/kg IV bolus then 18 units/kg/hour adjusted to an aPTT of 1.5 to 2.5 times control for massive embolism, near delivery, or creatinine clearance below 30 mL/minute; prophylaxis for high risk women: enoxaparin 40 mg subcutaneous daily (20 mg below 50 kg, 60 mg for 91 to 130 kg, 80 mg for 131 to 170 kg, 0.6 mg/kg above 170 kg); after delivery warfarin 5 mg oral daily with overlap of enoxaparin for at least 5 days until the INR is 2 to 3 for 24 hours; do not use warfarin in pregnancy or direct oral anticoagulants in pregnancy or breastfeeding.
• Procedures: inferior vena cava filter if anticoagulation is contraindicated; thrombolysis for massive pulmonary embolism with shock; stop therapeutic enoxaparin 24 hours before induction or caesarean section and prophylactic doses 12 hours before; restart 4 hours after epidural catheter removal and not sooner than 4 hours after vaginal birth.
• Special groups: renal impairment uses unfractionated heparin or enoxaparin 20 mg subcutaneous daily with anti-Xa monitoring; platelets falling by 50 percent after day 5 of heparin suggest heparin induced thrombocytopenia and need specialist anticoagulation; women with mechanical heart valves need specialist anticoagulation.
• Red flags: breathlessness, chest pain, haemoptysis, syncope, leg swelling that spreads, bleeding, severe headache, labour pains while on therapeutic dose.
• Follow-up: platelet count at day 7 to 14 on heparin; review every 4 weeks; plan delivery with anaesthetist; review at 6 weeks postpartum.