GGC Medicines

Adult Therapeutics Handbook

Prevention and Management of Venous Thromboembolism in Pregnancy

Please note: this guideline has exceeded its review date and is currently under review by specialists. Exercise caution in the use of the clinical guideline.

Prevention and Management of Venous Thromboembolism in Pregnancy

The full guideline on 'Thromboembolic Disease in Pregnancy and Puerperium' is available via NHSGGC StaffNet / Acute / Women and Children's Services / Obstetrics / GGC obstetric guidelines.


Venous thromboembolism (VTE) is a major cause of maternal death in the United Kingdom. Clinical assessment and diagnosis of women presenting with suspected VTE in pregnancy is unreliable and clinical suspicion must always be confirmed by appropriate objective testing. The signs and symptoms of VTE include: leg pain and swelling (usually unilateral), lower abdominal pain, low grade pyrexia, dyspnoea, chest pain, haemoptysis and collapse.

In prophylaxis of VTE in pregnancy, enoxaparin or tinzaparin is used. Before initiating prophylactic therapy, seek specialist advice to discuss doses and monitoring during pregnancy.

Prevention of VTE in pregnancy

  • Assessment of risk factors for VTE is usually made at booking, throughout pregnancy and in the postnatal period (see full guideline on NHSGGC StaffNet for details on risk factors).
  • Thrombophillia screen at booking should be considered in women with either:
    • A family history of both VTE and thrombophillia or
    • A family history of VTE in a 1st degree relative which was unprovoked or provoked by a minor risk factor (e.g. hormone-related [including pregnancy], minor trauma or long distance travel).
  • Women with a personal history of VTE which was unprovoked or provoked by a minor risk factor should be tested for antithrombin deficiency and antiphospholipid antibodies as these are the only thrombophilias which, if present, could alter management during pregnancy.
  • Women with several risk factors for VTE may require antithrombotic therapy antenatally and/or postnatally: low molecular weight heparin (LMWH) or unfractionated heparin (UFH). See full guideline on NHSGGC StaffNet / Acute / Women and Children's Services / Obstetrics / GGC obstetric guidelines.

Investigation of suspected VTE

  • Send for FBC, U&Es, coagulation screen, LFTs
  • After checking patient's bloods and whilst awaiting results of diagnostic test (as outlined below), commence anticoagulation therapy (see Drug therapy / treatment options section of this guideline).

Diagnosis of VTE in pregnancy

  • If Deep Vein Thrombosis (DVT) is suspected:
    • compression Duplex ultrasound is the primary diagnostic test. If ultrasound confirms DVT diagnosis then continue anticoagulating.
    • if ultrasound is negative but a high level of clinical suspicion remains, anticoagulant treatment should be discontinued but the ultrasound should be repeated between day 5 and 7. If repeat testing is negative, no further treatment is required. If repeat testing confirms DVT, anticoagulant treatment should be recommenced and continued.
    • when iliac vein thrombosis is suspected, (back pain and swelling of the entire limb) magnetic resonance venograph or conventional contrast venography may be considered.
  • If Pulmonary Embolism (PE) is suspected:
    • perform a chest x-ray and electrocardiogram. Pulse oximetry is often more useful and safer than arterial blood gases.
    • a troponin should also be checked to assess for other causes of chest symptoms and to assess the severity of any PE that might subsequently be diagnosed. A raised troponin level indicates a higher level of severity.
    • if the chest x-ray is normal, PE is still suspected and there are symptoms and/or signs of DVT then leg Doppler scans should be performed. If these show a DVT, anticoagulant treatment should be continued and further radiological investigations are not required.
    • if the chest x-ray is normal, PE is still suspected and there are no symptoms and/or signs of DVT, then a ventilation / perfusion scan (V/Q scan) or CT-pulmonary angiography (CTPA) should be performed. V/Q scanning is first-line investigation for suspected PE in all maternity units within NHSGGC. If the patient has an abnormal chest x-ray or is unstable, a CTPA is the investigation of choice.
  • If a V/Q scan or CTPA is required, the woman should be counselled with regard to the risk of radiation exposure both to her and her unborn baby.
  • Testing for D-dimer and performing a thrombophillia screen in the acute situation, should not be performed.

General management

Following DVT, the leg should be elevated, mobilisation encouraged and the fitting of a graduated elastic compression stocking on the affected leg organised via an orthotics department (or an equivalent locally available service). In the prevention of post-thrombotic syndrome, women should be advised that LMWH may be more beneficial when compared to warfarin, but the role of compression stockings is unclear.

Drug therapy / treatment options

Treatment of VTE in pregnancy

  1. Start treatment with a LMWH:
  • Initial dose of enoxaparin SC is either a twice daily regimen (1mg/kg 12 hourly) or a once daily regimen (1.5mg/kg/day). Check with local obstetric team which regimen is preferred before prescribing, then using early pregnancy weight:
    • see table 1 below for details of the twice daily regimen
    • for once daily regimen (1.5mg/kg/day) and weight is <125kg, choose appropriate prefilled syringe dose size (sizes available include 60mg, 80mg, 100mg, 120mg and 150mg). If the syringe dose is +/- 10% of correct dose, check anti-factor Xa levels approximately 4 hours post dose after at least 3 doses have been given (target range 0.5–1units/ml). 
    • for once daily regimen (1.5mg/kg/day) and weight >125kg - discuss with haematologist. 

Table 1: Twice daily enoxaparin regimen

Early pregnancy weight Initial dose of enoxaparin
<50kg 40mg twice daily
50-69kg 60mg twice daily
70-89kg 80mg twice daily
90-109kg 100mg twice daily
110-125kg 120mg twice daily
>125kg Discuss with haematologist
  • Initial dose of tinzaparin: 175units/kg once daily. Use early pregnancy weight.
  1. Monitor LMWH therapy. Routine measurement of peak anti-factor Xa activity for patients on LMWH for treatment of acute VTE in pregnancy or post-partum is not recommended but can be requested if:
    • obstetric patient is at extremes of body weight (<50kg and ≥90kg).
    • obstetric patient has other complicating factors which puts her at high risk (e.g. renal impairment, recurrent VTE).
    • if once daily dosing is commenced and the pre-filled syringe dose is +/- 10% of calculated dose
  2. Platelets - Obstetric patients receiving LMWH or UFH (unless receiving UFH post-op) do not require routine platelet monitoring for heparin-induced thrombocytopenia.
  3. Continue full dose LMWH throughout pregnancy.
  4. Labour, caesarean section, and regional anaesthesia – inform the on-call obstetric team of this patient and see the full guideline on NHSGGC StaffNet for details.
  5. High risk of haemorrhage – discuss patient with specialists and also refer to the full guideline on NHSGGC StaffNet.
  6. Postnatal anticoagulation – anticoagulant therapy should be continued for the duration of the pregnancy and for at least 6 weeks postnatally and until at least 3 months of treatment has been given in total. Refer to the full guideline on NHSGGC StaffNet for information regarding postnatal treatment choice.

    Patients developing VTE in pregnancy should be referred to the haematology clinic or obstetric medical / haematology clinic for follow up investigations (including thrombophilia testing, if appropriate, once heparin treatment has been discontinued) and anti-factor Xa activity if appropriate.