In addition to these evidence-based recommendations, the guideline development group also identifies points of best clinical practice in the original guideline document.
Levels of evidence and grading of recommendations (A–D) are defined at the end of the "Major Recommendations" field.
Prepregnancy and Antenatal Risk Assessment
What Are the Risk Factors for Venous Thromboembolism (VTE) in Pregnancy and the Puerperium? What Is the Magnitude of Risk for These Factors?
The risk factors for VTE are listed in the table below. For most risk factors the level of evidence is 2+ but it varies from 2– to 2++ depending on the risk factor.
Table: Risk Factors for Venous Thromboembolism in Pregnancy
Protein C deficiency
Protein S deficiency
Factor V Leiden
Prothrombin gene G20210 A
Acquired (antiphospholipid syndrome)
Persistent lupus anticoagulant
Persistent moderate/high-titre anticardiolipin antibodies or beta2 glycoprotein 1 antibodies
Medical comorbidities (e.g., heart or lung disease, SLE, cancer, inflammatory conditions (inflammatory bowel disease or inflammatory polyarthropathy), nephrotic syndrome (proteinuria >3 g/day), sickle cell disease, intravenous drug user
Age >35 years
Obesity (BMI >30 kg/m2) either prepregnancy or in early pregnancy
Gross varicose veins (symptomatic or above knee or with associated phlebitis, oedema/skin changes)
||Multiple pregnancy, assisted reproductive therapy
PPH (>1 litre) requiring transfusion
|Prolonged labour, mid-cavity rotational operative delivery
||Surgical procedure in pregnancy or puerperium (e.g., ERPC, appendicectomy, postpartum sterilisation)
Ovarian hyperstimulation syndrome
Admission or immobility (≥ 3 days' bed rest) (e.g., symphysis pubis dysfunction restricting mobility)
Systemic infection (requiring antibiotics or admission to hospital) (e.g., pneumonia, pyelonephritis, postpartum wound infection)
Long-distance travel (> 4 hours)
BMI = body mass index; ERPC = evacuation of retained products of conception; PPH = postpartum haemorrhage; SLE = systemic lupus erythematosus
aMay develop at later stages in gestation than the initial risk assessment or may resolve and therefore continuing individual risk assessment is important
Admission to Hospital
C - All women should undergo a documented assessment of risk factors for VTE in early pregnancy or before pregnancy. This assessment should be repeated if the woman is admitted to hospital for any reason or develops other intercurrent problems. The assessment should be repeated again intrapartum or immediately postpartum.
C - Any woman with three or more current or persisting risk factors shown in Figure 1 of the original guideline and the table above (other than previous VTE or thrombophilia) should be considered for prophylactic low-molecular-weight heparin (LMWH) antenatally and will usually require prophylactic LMWH for 6 weeks postnatally; a postnatal risk reassessment should be made.
C - Any woman with two or more current or persisting risk factors shown in Figure 1 of the original guideline and the table above (other than previous VTE or thrombophilia) should be considered for prophylactic LMWH for at least 7 days postpartum.
Which Women with Prior VTE Require Thrombophilia Testing?
C - Women with a previous non-estrogen-related VTE provoked by a minor risk factor should undergo testing for thrombophilia, as this will influence management and decisions regarding thromboprophylaxis antenatally.
Recommendations for Women with a Previous VTE
C - Women with a previous single provoked (excluding estrogen-related) VTE (and no other risk factors) require close surveillance antenatally and thromboprophylaxis with LMWH for 6 weeks postpartum.
C - Women with previous recurrent VTE or a previous unprovoked or estrogen/pregnancy-related VTE or a previous VTE and a history of VTE in a first-degree relative (or a documented thrombophilia) or other risk factors should be offered thromboprophylaxis with LMWH antenatally and for 6 weeks postpartum.
Asymptomatic Heritable Thrombophilia — How Should Women with Asymptomatic Thrombophilia Be Treated?
C - Women with asymptomatic inherited thrombophilia without other risk factors may be managed with close surveillance antenatally but should be considered for LMWH for at least 7 days postpartum.
Exceptions are in women with antithrombin deficiency or more than one thrombophilic defect (including homozygous factor V Leiden, homozygous prothrombin G20210A and compound heterozygotes) or those with additional risk factors where advice of a local expert should be sought and antenatal prophylaxis considered.
Recommendations on Thrombophilia
C - Women should be stratified according to level of risk associated with their thrombophilia and the presence or absence of a family history or other risk factors.
C - If thromboprophylaxis is given antenatally for a persisting risk factor, it should be continued postpartum for 6 weeks.
Acquired Thrombophilia (Antiphospholipid Syndrome) — How Should Women with Antiphospholipid Syndrome Be Treated?
C - Women with previous thromboses and antiphospholipid syndrome should be offered both antenatal and 6 weeks of postpartum thromboprophylaxis. Women with persistent antiphospholipid antibodies with no previous VTE and no other risk factors or fetal indications for LMWH may be managed with close surveillance antenatally but should be considered for LMWH for 7 days postpartum.
Timing of Initiation of Thromboprophylaxis
When Should Thromboprophylaxis Be Started?
B - Antenatal thromboprophylaxis should begin as early in pregnancy as practical.
Thromboprophylaxis after Delivery
For How Long Should Thromboprophylaxis Be Continued after Delivery?
C - Thromboprophylaxis should be continued for 6 weeks in women at high risk of postpartum VTE and for 1 week in women with intermediate risk.
Which Women with Previous VTE Need Postpartum Thromboprophylaxis?
C - All women with a previous history of confirmed VTE should be offered thromboprophylaxis with LMWH or warfarin for 6 weeks postpartum, regardless of the mode of delivery.
Which Women with Thrombophilia without Previous VTE Need Postpartum Thromboprophylaxis?
C - All women with known heritable or acquired thrombophilia should be considered for LMWH for at least 7 days following delivery, even if they were not receiving antenatal thromboprophylaxis. This could be extended to 6 weeks if there is a family history or other risk factors present.
What Is the Magnitude of Risk of VTE after Caesarean Section?
C - All women who have had an emergency caesarean section (category 1–3) should be considered for thromboprophylaxis with LMWH for 7 days after delivery.
C - All women who have had an elective caesarean section (category 4) who have one or more additional risk factors (such as age over 35 years, BMI greater than 30) should be considered for thromboprophylaxis with LMWH for 7 days after delivery.
Which Agents Should Be Used for Thromboprophylaxis?
B - LMWHs are the agents of choice for antenatal thromboprophylaxis. They are at least as effective as and safer than unfractionated heparin.
Agents for Postpartum Thromboprophylaxis
Which Agents Are Appropriate for Postpartum Thromboprophylaxis?
C - LMWH is appropriate for postpartum thromboprophylaxis although, if women are receiving long term anticoagulation with warfarin, this can be started when the risk of haemorrhage is low, usually 5–7 days after delivery.
B - Both warfarin and LMWH are safe when breastfeeding.
Grades of Recommendation
At least one meta-analysis, systematic review or randomised controlled trial rated as 1++ and directly applicable to the target population; or
A systematic review of randomised controlled trials or a body of evidence consisting principally of studies rated as 1+, directly applicable to the target population and demonstrating overall consistency of results
A body of evidence including studies rated as 2++ directly applicable to the target population and demonstrating overall consistency of results; or
Extrapolated evidence from studies rated as 1++ or 1+
A body of evidence including studies rated as 2+ directly applicable to the target population and demonstrating overall consistency of results; or
Extrapolated evidence from studies rated as 2++
Evidence level 3 or 4; or
Extrapolated evidence from studies rated as 2+
Classification of Evidence Levels
1++ High-quality meta-analyses, systematic review of randomised controlled trials or randomised controlled trials with a very low risk of bias
1+ Well-conducted meta-analyses, systematic reviews of randomised controlled trials or randomised controlled trials with a low risk of bias
1- Meta-analyses, systematic reviews of randomised controlled trials or randomised controlled trials with a high risk of bias
2++ High-quality systematic reviews of case–control or cohort studies or high quality case–control or cohort studies with a very low risk of confounding, bias or chance and a high probability that the relationship is causal
2+ Well-conducted case–control or cohort studies with a low risk of confounding, bias or chance and a moderate probability that the relationship is causal
2- Case–control or cohort studies with a high risk of confounding, bias or chance and a significant risk that the relationship is not causal
3 Non-analytical studies; e.g. case reports, case series
4 Expert opinion