Definition Venous thromboembolism (VTE) is a condition in which a blood clot (thrombus) develops, commonly in the deep veins of the lower limbs, and this is called deep vein thrombosis (DVT). The majority of DVT in pregnancy are iliofemoral with a greater risk of both embolisation and recurrence. A thrombus may detach from its site of origin in the vein (embolus) and migrate through the blood stream to reach the lungs (pulmonary thromboembolism [PTE]). Venous thromboembolism has multiple contributory risk factors.
Acute DVT occurs in one of the three major paired veins, below the popliteal vein (posterior tibial, anterior tibial, peroneal) in the calf.
Proximal venous thrombosis
Acute DVT occurs in the popliteal vein or higher: superficial femoral or common femoral vein, iliac vein and vena cava.
Upper extremity venous thrombosis
They are generally classified separately from classic DVT. They occur above the right atrium, most frequently in the subclavian, axillary or internal jugular veins.
Incidence: 1–2 per 1000 pregnancies
Identification of women at increased risk of arterial thrombosis
Identification of women at increased risk of bleeding while on treatment with anticoagulants
Hospitalisation and access to high dependency unit (HDU) care secondary to low oxygen lung perfusion
Post-thrombotic syndrome including leg pain, swelling, dermatitis, dependent cyanosis, ulcers and varicosities (risk 30%–60%)
Major postpartum haemorrhage (1.98%)
Osteoporosis-related fractures (0.04%)
Heparin-induced thrombocytopenia (HIT) which is substantially lower with use of low-molecular-weight heparin (LMWH)
Allergic skin reaction (1.8%)
Increased life-time risk of breast cancer 13.6% (background risk of 1/200) with computerized tomography pulmonary angiography (CTPA)
A ventilation–perfusion (V/Q) scan carries an increased risk as compared to CTPA of childhood cancers to 1 per 280,000 (background risk of 1 per 1,000,000).
The radiation dose to the fetus from a chest x-ray performed during pregnancy is negligible.
Hypothyroidism if iodinated contrast medium is used with CTPA.
Fetal death: from the use of thrombolytic agents.
Patients should be informed about all aspects of VTE including seriousness of the disease process, risks related to each investigation and their implications. Counselling should include treatment benefits and risks. Every effort should be made to help women make informed choices about every aspect of their management where appropriate [1, 2].
Patients who had a suspected DVT but negative ultrasound and on no treatment should be advised that they should seek urgent advice and further assessment if they develop symptoms consistent with VTE such as increased limb pains or swelling, sudden onset of breathlessness, chest or back pain, coughing or spitting up blood and any episode of collapse.
Explain to the woman about the increased risk of VTE while using combined oral contraceptives/ hormone replacement treatment.
Magnitude of the Problem
There is an approximately 10-fold increased risk during pregnancy compared with non-pregnant and 25-fold increased risk compared with non-pregnant/ non-puerperal during puerperium, and this risk is considerably increased among women with known thrombophilia. Pulmonary embolism has been the leading direct cause of maternal death in the UK (1.56 per100 000 maternities) [3, 4].
Antenatal Screening and Thromboprophylaxis
The rationale for prophylaxis is based on its efficacy, the clinically silent nature of VTE, its prevalence in pregnant or puerperal patients and its potentially disabling or fatal consequences. More than 40% of antenatal VTE occur in the first trimester of pregnancy. The confidential enquiries into maternal deaths report in the United Kingdom found that two-thirds of antenatal fatal pulmonary embolism occurred in the first trimester . Therefore, every effort should be made to instigate antenatal thromboprophylaxis in the first trimester of pregnancy. Antenatal risk assessment should start at the time of first booking visit to the hospital. Women with multiple risk factors (three or more), those with a previous unprovoked VTE or previous recurrent VTE and those with multiple thrombophilia defects should be offered thromboprophylaxis with LMWH antenatally .
Furthermore, women with a history of recurrent VTE who are on warfarin should be switched over to LMWH as soon as pregnancy is confirmed.
All known identifiable risk factors for VTE have to identified at the booking visit (Table 3.1). These can be classified at high, intermediate or low risk for VTE and managed accordingly. Each woman’s risks need to be continually reviewed throughout pregnancy and during the intrapartum period. A note should also be made of conditions that can increase complications following thromboprophylaxis.
|Antenatal risk assessment for venous thromboembolism: adjusted odds ratio where available|
|High risk||Intermediate risk||Low risk|
Single previous VTE (AOR: 24)
Thrombophilia or family history
Previous recurrent VTE (>1)
Requires antenatal prophylaxis with LMWH
Single previous VTE with no family history or
Thrombophilia + but no VTE
Medical comorbidities, e.g. heart or lung disease, systemic lupus erythematosus (AOR:8.7), inflammatory conditions, nephrotic syndrome, sickle cell disease, chronic HIV, intravenous drug user
Surgical procedure, e.g. appendicectomy
Consider antenatal prophylaxis with LMWH
Seek expert team advice
Obesity BMI>30 kg/m2): 2- to 5-fold increase
Parity ≥3 (AOR: 3.4)
Smoker (10–30/day): (AOR 1.4, 3.4)
Gross varicose veins (AOR: 2.7), current systemic infection
Heterozygous factor V Leiden and prothrombin G20210 A without prior Hx of VTE (risk <1%)
Immobility, e.g. paraplegia, symphysis pubis
Dysfunction with immobility, long-distance travel, dehydration/hyperemesis
Preeclampsia (AOR: 2.9, 3.1)
Multiple pregnancy/assisted reproductive treatment
Mobilisation and avoidance of dehydration: three or more risk factors, treat as intermediate
Additional intrapartum risk factors
Preeclampsia (AOR: 2.9, 3.1)
Dehydration/hyperemesis/OHSS (AOR: 2.5)
Multiple pregnancy or assisted reproduction (ART)
Caesarean section in labour (AOR: 2.7, 3.6)
Elective caesarean section (AOR:2.1)
Mid-cavity or rotational forceps
Prolonged labour (>24 hours)
PPH (>1 L or blood transfusion) (AOR: 4.1)
Identification of women at increased bleeding risk when on anticoagulation treatment
Haemophilia or other known bleeding disorder (e.g. von Willebrand’s disease or acquired coagulopathy)
Active antenatal or postpartum bleeding
Women considered at increased risk of major haemorrhage
(e.g. placenta praevia)
Thrombocytopenia (platelet count <75 × 109)
Acute stroke in previous 4 weeks (haemorrhagic or ischaemic)
Severe renal disease (glomerular filtration rate <30 mL/minute/1.73 m2)
Severe liver disease (prothrombin time above normal range or known varices)
Uncontrolled hypertension (blood pressure > 200 mm Hg systolic or >120 mm Hg diastolic)
Transient risk factors
Postpartum infection (AOR: 4.1)
Immobility (AOR: 7.7)
Surgical procedure in pregnancy + haemorrhage or ≤6 weeks postpartum (AOR: 6.2, 12)
Obstetric haemorrhage (AOR: 9); transfusion (AOR: 7.6)
Antenatal and postnatal prophylactic dose of LMWH
Weight <50 kg = 20 mg enoxaparin/2500 units of dalteparin/3500 units of tinzaparin daily
Weight 50–90 kg = 40 mg enoxaparin/5000 units of dalteparin/4500 units of tinzaparin daily
Weight 91–130 kg = 60 mg enoxaparin/7500 units of dalteparin/7000 units of tinzaparin daily
Weight 131–170 kg = 80 mg enoxaparin/10 000 units of dalteparin/9000 units of tinzaparin daily
Weight >170 kg = 0.6 mg/kg/day enoxaparin; 75 units/kg/day dalteparin/75 units/kg/day of tinzaparin
AOR, adjusted odds ratio; LMWH, low-molecular-weight heparin; OHSS, ovarian hyperstimulation syndrome; PPH, postpartum haemorrhage; VTE, venous thromboembolism.