Chapter 2: Thrombosis and thromboembolism

Annex 2.1 

Summary of the key recommendations of the Royal College of Obstetricians and Gynaecologists (RCOG) guidelines for thromboprophylaxis in pregnancy, labour and after vaginal delivery and caesarean section
Thromboprophylaxis during pregnancy, labour and after normal vaginal delivery3.

Risk factors for venous thromboembolisma in pregnancy and the puerperiuma1.

New onset or transientb
  • Previous VTE
  • Thrombophilia
    • Congenital
      • Antithrombin deficiency
      • Protein C deficiency
      • Protein S deficiency
      • Factor V Leiden
      • Prothrombingene variant
    • Acquired
      • antiphospholipid syndrome
  • Lupus anticoagulant
  • Anticardiolipin antibodies
  • Age over 35 years
  • Obesity (BMI over 30kg/m2) either pre-pregnancy or in early pregnancy
  • Parity over 4
  • Gross varicose veins
  • Paraplegia
  • Sickle cell disease
  • Inflammatory disorders e.g. inflammatory bowel disease
  • Some medical disorders e.g. nephritic syndrome, certain cardiac diseases
  • Myeloproliferative disorders, e.g. essential thrombocythaemia, polycthaemia rubra vera
  • Surgical procedure in pregnancy or puerperium
  • e.g. evacuation of retained products of conception, postpartum sterilization,
  • Hyperemesis
  • Dehydration
  • Ovarian hyperstimulation syndrome
  • Severe infection, e.g. pyelonephritis
  • Immobility (over 4 days bed rest)
  • Pre-eclampsia
  • Excessive blood loss
  • Prolonged labourc
  • Mid-cavity instrumental deliveryc
  • Immobility after deliveryc

aAlthough these are all accepted as thromboembolic risk factors, there are few data to support the degree of increased risk associated with many of them.

bThese risk factors are potentially reversible and may develop at later stages in gestation than the initial risk assessment or may resolve; an ongoing individual risk assessment is important.

cRisk factors specific to postpartum VTE only.


All women should undergo an assessment of risk factors for VTE in early pregnancy or before pregnancy.  This assessment should be repeated if the woman is admitted to hospital or develops other intercurrent problems. (C)

Women with previous VTE should be screened for inherited and acquired thrombophilia, ideally before pregnancy. (B)

Regardless of their risk of VTE, immobilisation of women during pregnancy, labour and the puerperium should be minimised and dehydration should be avoided. (GPP)

Women with previous VTE should be offered postpartum thromboprophylaxis with LMWH.  It may be reasonable not to use antenatal thromboprophylaxis with heparin in women with a single previous VTE associated with a temporary risk factor that has now resolved. (C)

Women with previous recurrent VTE or a previous VTE and a family history of VTE in a first-degree relative should be offered thromboprophylaxis with LMWH antenatally, and for at least six weeks postpartum. (C)

Women with previous VTE and thrombophilia should be offered thromboprophylaxis with LMWH antenatally and for at least six weeks postpartum. (B)

Women with asymptomatic inherited or acquired thrombophilia may qualify for antenatal or postnatal thromboprophylaxis, depending on the specific thrombophilia and the presence of other risk factors. (C)

Women with three or more persisting risk factors should be considered for thromboprophylaxis with LMWH antenatally and for three to five days postpartum. (GPP)

Women should be reassessed before or during labour for risk factors for VTE. Age over 35 years and BMI greater than 30 or a body weight greater than 90Kg are important independent risk factors for postpartum VTE even after vaginal delivery.  The combination of either of these risk factors with any other risk factor for VTE (such as pre-eclampsia or immobility) or the presence of two other persisting risk factors should lead the clinician to consider the use of LMWH for three to five days postpartum. (GPP)

Antenatal thromboprophylaxis should begin as early in pregnancy as practical.  Postpartum prophylaxis should begin as soon as possible after. (B)

LMWHs are the agents of choice for antenatal thromboprophylaxis. They are as effective as and safer than unfractionated heparin in pregnancy. (B)

Warfarin should usually be avoided during pregnancy. It is safe after delivery and during breastfeeding. (B)

Once the woman is in labour or thinks she is in labour, she should be advised not to inject any further heparin.  She should be reassessed on admission to hospital and further doses should be prescribed by medical staff. (GPP)

The grades of recommendations (B or C) are as follows:

Requires the availability of well controlled clinical studies but no randomised clinical trials on the topic of recommendations (Evidence levels IIa, IIb, III).
Requires evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities. Indicates an absence of directly applicable clinical studies of good quality (Evidence level IV).
The other recommendations represent Good Practice Points (GPP), i.e. recommended best practice based on the clinical experience of the guideline development group.

For further details, see the full Report 3.

Prophylaxis against thromboembolism in caesarean section

The following recommendations, taken from the RCOG Working Party Report on prophylaxis against thromboembolism5, are widely used for risk assessment and are of relevance to women requiring caesarean section. It is important to note that the 2004 guideline3 updates and replaces previous guidance on dosage of thromboprophylaxis.

Box 2.1.1

RCOG Risk assessment profile for thromboembolism in caesarean section

Low risk - Early mobilisation and hydration
Elective caesarean section - uncomplicated pregnancy and no other risk factors

Moderate risk – Consider one of a variety of prophylactic measures


High risk – Heparin prophylaxis +/- leg stockings

Management of different risk groups

Low risk patients

Patients undergoing elective caesarean section with uncomplicated pregnancy and no other risk factors require only early mobilisation and attention to hydration.

Moderate risk patients

Patients assessed as of moderate risk should receive subcutaneous heparin (doses are higher during pregnancy) or mechanical methods. Dextran 70 is not recommended until after the delivery of the fetus and is probably best avoided in pregnant women.

High risk patients

Patients assessed as high risk should receive heparin prophylaxis and, in addition, leg stockings would be beneficial.

Prophylaxis until the fifth postoperative day is advised (or until fully mobilised if longer).

The use of subcutaneous heparin as prophylaxis in patients with an epidural or spinal block remains contentious. Evidence from general and orthopaedic surgery does not point to an increased risk of spinal haematoma.