Assessment of venous thromboembolism risk and prevention of deep vein thrombosis in childbirth
All pregnant women have a risk of thrombosis from the first trimester until at least 6 weeks postpartum, the absolute risk being 1 : 1000 pregnancies.
The factors contributing to venous thromboembolism (VTE) include immobility, stasis of blood flow, alteration of the constituents of the blood (hypercoagulability) and abnormalities/damage to the vessel wall; all of these are affected by pregnancy. An increase in coagulation factors, with a decrease in natural inhibitors to anticoagulation, reduced venous tone and the pressure of the pregnant uterus all predispose to VTE. If left untreated, 25% of deep vein thrombosis (DVT) will be complicated by pulmonary embolism (PE), where a fragment of thrombus breaks away (Figure 70.1) and travels through the right side of the heart to lodge in the pulmonary circulation. The risk factors are listed in Table 70.1.
NICE (2015), RCOG (2015) and SIGN (2010) recommend that all pregnant women should undergo a thrombotic risk assessment with numerical scoring at the first antenatal visit or prepregnancy wherever possible (Table 70.1). This assessment should consider personal and family history, the presence of any risk factors and any known thrombophilia, balancing with the risk of bleeding. If the woman’s circumstances change, such as excessive weight gain, immobility or vomiting with dehydration, or admittance to hospital, then assessment should be repeated. Once the baby is born, a further risk assessment should be undertaken. All details should be documented in her records.
If assessment identifies a risk of developing VTE or bleeding, the midwife should refer the woman to a specialist haematologist. Based on the numerical scoring from the thrombotic risk assessment, NICE recommend pharmacological VTE thromboprophylaxis with low molecular weight heparin (LMWH) or unfractionated heparin (UFH) for those with renal failure, as follows:
- From the first trimester if the total score ≥4
- From 28 weeks, if the total score is 3 antenatally
- For at least 10 days, if the total score is ≥2 postnatally.
- If admitted to hospital antenatally
- If prolonged admission ≥3 days or readmission to hospital within the puerperium.