RecommendationConsider offering pharmacological VTE prophylaxis with LMWH (or UFH for patients with renal failure) to women who are pregnant or have given birth within the previous 6 weeks who are admitted to hospital but are not undergoing surgery, and who have one or more of the following risk factors:
  • expected to have significantly reduced mobility for 3 or more days
  • active cancer or cancer treatment
  • age over 35
  • critical care admission
  • dehydration
  • excess blood loss or blood transfusion
  • known thrombophilias
  • obesity (pre-pregnancy or early pregnancy BMI over 30 kg/m2)
  • one or more significant medical comorbidities (for example: heart disease; metabolic, endocrine or respiratory pathologies; acute infectious diseases; inflammatory conditions)
  • personal history or a first-degree relative with a history of VTE
  • pregnancy-related risk factor (such as ovarian hyperstimulation, hyperemesis gravidarum, multiple pregnancy or pre-eclampsia)
  • varicose veins with phlebitis.
Relative Values of OutcomesThe outcomes identified as important by the Guideline Development Group included thromboembolic events (asymptomatic and symptomatic DVT, symptomatic pulmonary embolism and fatal pulmonary embolism), bleeding events (major bleeding, fatal bleeding and stroke) and other long term events occurring as a result of VTE (chronic thromboembolic pulmonary hypertension and post thrombotic syndrome).
Trade off between clinical benefit and harmsThe benefits of reducing the risk of VTE and long term consequences were considered against potential harmful effects to both the mother and her unborn child (if the admission was antenatal).
Economic considerationsA cost effectiveness analysis was not completed specifically for this population subgroup. However, the cost-effectiveness model for medical patients indicates that prophylaxis with LMWH is cost-effective for patients at increased risk.
Quality of evidenceNo RCT studies on methods of prophylaxis were found in pregnant or postpartum women admitted to hospital not undergoing surgery.
The recommendations were developed based on the expert consensus. These are supported by epidemiological studies although no systematic review of these studies was completed.
Other considerationsPregnancy and the postpartum period (up to and including 6 weeks after delivery) have been identified as an independent risk factor for VTE. If these patients are admitted and have one of the risk factors listed, they should be considered for prophylaxis. Most women having vaginal deliveries will not require an extended stay in hospital and women are unlikely to have restricted mobility for extended periods of time.
The risk factors for VTE within the recommendation are similar to those used for other hospitalised patients. The evidence for these factors is reviewed in section 5.7.
The risk factors added or modified are based on additional information presented within section 30.2 specifically for pregnant women and those ≤6 weeks postpartum. The age criterion of 35 was added as the evidence suggests that this is when pregnant women are at increased risk. Two other risk factors were added; excess blood loss or blood transfusion and other specific pregnancy related risk factors. The evidence for these are discussed in section 30.2
Choice of prophylactic agents
The summary of product characteristics contains further information on the use of pharmacological prophylaxis agents during pregnancy and postpartum.
LMWH: Although it has not been tested extensively in this population, low molecular weight heparin (LMWH) is regarded as the most appropriate prophylaxis for pregnant women. LMWH has been used widely in pregnancy and is considered to be relatively safe. It is preferred over over unfractionated heparin, due to its better safety profile and convenience235 the summary of product characteristics indicates that animal studies have not shown evidence of fetotoxicity or teratogenicity. Heparin induced thrombocytopenia (HIT) with LMWH has not been reported and the risk of osteoporotic fracture with LMWH is known to be much lower than the risk with unfractionated heparin (UFH), although the actual risk is uncertain.
Fondaparinux: There is inadequate safety information for the use of fondaparinux during pregnancy and should not be prescribed unless clearly necessary.
Warfarin: has been identified to have teratogenic and bleeding risks to the foetus and should not be used without a careful risk-benefit analysis and discussion with the patient.
Prophylaxis dosing:
There is debate about the appropriate frequency and size of doses of LMWH in pregnancy due to inadequate information from clinical trials. Due to the increased plasma volume, increased glomerular filtration rate and, therefore, decreased half-life of LMWH during pregnancy, dose adjustment (based on weight) may be necessary. More details are available in the summary of product characteristics and the in the RCOG green-top guidelines563.

From: 30, Pregnancy and up to 6 weeks post partum

Cover of Venous Thromboembolism
Venous Thromboembolism: Reducing the Risk of Venous Thromboembolism (Deep Vein Thrombosis and Pulmonary Embolism) in Patients Admitted to Hospital.
NICE Clinical Guidelines, No. 92.
National Clinical Guideline Centre – Acute and Chronic Conditions (UK).
Copyright © 2010, National Clinical Guideline Centre - Acute and Chronic Conditions.

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