Deep Vein Thrombosis in Pregnancy

Deep vein thrombosis in pregnancy is a clot in the deep veins of the leg or pelvis, caused by hypercoagulability, venous stasis and vessel injury. It occurs in about 1 in 1000 pregnancies, is mostly left sided and often involves the iliofemoral veins, which carry a high risk of embolism. It matters because untreated disease causes pulmonary embolism and post thrombotic syndrome.

• Risk factors: previous thrombosis, thrombophilia, obesity, immobility, caesarean section, preeclampsia, infection, dehydration, assisted conception.
• The left leg is involved in most cases.
• Occurs in all trimesters, with a rise after caesarean delivery.

Women have unilateral leg swelling, pain, warmth and tenderness along the deep veins, sometimes with lower abdominal or back pain from pelvic vein extension. A swollen, blue, painful leg suggests iliofemoral disease.

• Calf circumference more than 2 cm larger than the other side.
• Pitting oedema confined to one leg.
• Differential diagnosis: cellulitis, superficial thrombophlebitis, muscle strain, ruptured Baker cyst, lymphoedema, physiological oedema, compartment syndrome.
• Complications: pulmonary embolism, post thrombotic syndrome, phlegmasia cerulea dolens, recurrence, bleeding on anticoagulation.

The approach is compression ultrasound with clinical probability.

• Compression duplex ultrasound of the leg veins; if negative and iliac vein thrombosis is suspected, use Doppler flow in the common femoral vein and magnetic resonance venography.
• Repeat ultrasound at 3 and 7 days if negative and symptoms continue.
• Left leg, calf circumference difference of 2 cm or more, and presentation in the first trimester each raise the likelihood; absence of all three makes deep vein thrombosis unlikely.
• Full blood count, creatinine, liver enzymes, coagulation screen and weight before treatment.

The principle is immediate full dose low molecular weight heparin for the rest of pregnancy and for 6 weeks after delivery.

• Supportive: elevate the leg; walk once anticoagulated; graduated compression stockings of 20 to 30 mmHg for pain and swelling; fluids; stop smoking.
• Pharmacological: enoxaparin 1 mg/kg subcutaneous 12-hourly (booking weight) for the remainder of pregnancy and at least 6 weeks after delivery (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 extensive iliofemoral thrombosis, creatinine clearance below 30 mL/minute or near delivery; warfarin 5 mg oral daily after delivery with overlap of enoxaparin for 5 days until the INR is 2 to 3 for 24 hours; paracetamol 1 g oral 6-hourly (maximum 4 g in 24 hours); avoid NSAIDs and direct oral anticoagulants.
• Procedures: inferior vena cava filter if anticoagulation is contraindicated or thrombosis extends despite treatment; thrombolysis or thrombectomy for limb threatening phlegmasia; stop therapeutic enoxaparin 24 hours before induction or caesarean section and restart 24 hours after delivery; prophylactic doses stop 12 hours before and restart 4 hours after epidural catheter removal.
• Special groups: renal impairment uses unfractionated heparin; suspected heparin induced thrombocytopenia (platelets falling by 50 percent after day 5) needs specialist anticoagulation; breastfeeding is compatible with enoxaparin and warfarin.
• Red flags: breathlessness, chest pain, haemoptysis, syncope, blue or white painful leg, bleeding, severe headache.
• Follow-up: platelets at day 7 to 14; review every 4 weeks; anaesthetic plan by 36 weeks; review at 6 weeks postpartum.