Having read this chapter, the reader should be able to:
Restricted mobility can influence the development of a venous thromboembolism (VTE) which affects morbidity and mortality. During 2010–2012 VTE was the highest direct cause of maternal mortality in the UK with 26 women dying during 2010–2012 (Knight et al 2014) – almost a 50% increase in numbers since 2006–2008. The majority of deaths were from pulmonary embolism (PE), with two due to cerebral vein thrombosis. This chapter focuses on the principles of VTE prevention, discussing the physiological changes that occur during pregnancy and the risk factors which increase the likelihood of VTE developing and prophylactic measures that can be used – exercises, graduated compression stockings (GCS) and sequential compression devices.
A thrombosis (clot) forms in response to stasis of blood flow, altered coagulation status and/or damage to the blood vessel walls (known as Virchow’s triad), all of which are present at some point during pregnancy, labour and the postnatal period. Pregnancy is a state of hypercoagulability; there is a progressive change in the balance between anticoagulant and prothrombotic factors, an increase in fibrin deposition and decreased fibrinolysis, which create a procoagulant state (Arya 2011, Blackburn 2013). Blood flow in the lower limbs is reduced by up to 50% and venous distension during pregnancy can result in vessel wall damage, with further trauma occurring at delivery (Arya 2011). The changes to the coagulation factors begin with conception and may not return to their prepregnancy levels until 8 weeks following delivery (James 2011). The clot that forms is referred to as a deep vein thrombosis (DVT). If a part of the DVT breaks away, it is carried in the circulation to the major organs where it may lodge in a smaller vein causing ischaemia and may be referred to as an embolism.
During pregnancy the risk of a DVT increases four- to sixfold (Arya et al 2011, RCOG 2015) with the risk of a PE being 1.3 per 1000 pregnancies (RCOG 2015). While DVTs are often symptomatic, Meyer (2010) suggests the rates of asymptomatic DVT following surgery range from 10% for minor surgery, e.g. repair of third-degree tear, to 10–40% for major surgery, e.g. caesarean section. It is more common for a DVT to form in the left leg during pregnancy because of the increased pressure from the gravid uterus on the left common iliac vein but postnatally it can occur in either leg (Virkus et al 2013). Many antenatal VTEs occur during the first trimester (RCOG 2015), although Chan et al (2012) consider the incidence does not vary much across the trimesters. The Royal College of Obstetricians and Gynaecologists (RCOG 2015) advise the first 3 weeks postpartum is the highest risk period for VTE and PE formation, with the risk increased 22-fold.
Complications of DVT
The most serious complication is death; 3.5% of women who develop a PE during pregnancy through to the puerperium will die (RCOG 2015). Approximately 89% of the women who died during 2006–2008 had risk factors and care was substandard for 56% of women (Drife 2011). Thus it is important to identify women who are at high risk of VTE and manage them appropriately.
Post-thrombotic syndrome (PTS) is thought to occur in 20–50% of DVT events (Wik et al 2012). This develops from valve incompetence causing venous stasis resulting in chronic swelling and discomfort in the affected limb, with some limbs becoming ulcerated (Roswell & Law 2011). The use of GCS worn for 2 years following the DVT can reduce the incidence of PTS by 50% (Wik et al 2012).
The RCOG (2015) present a very comprehensible list of risk factors for VTE:
Potentially reversible factors
The RCOG (2015) recommend that all women have a documented assessment of risk factors for VTE in early pregnancy or, if possible, before pregnancy (Table 54.1). They advise the assessment should be repeated each time the woman is admitted to hospital or, if she develops other problems, in labour and following delivery, as her risk status may have changed (RCOG 2015). The Department of Health (2010) produced a national guideline for the National Health Service (NHS) Trusts to use for all patients on admission to hospital but do not include pregnancy-specific risk factors. The risk assessment should identify women at increased risk of developing a VTE and the RCOG (2015) recommend prophylactic treatment based on the degree of risk. However Bennett-Day (2011) argues the amount of high-grade evidence around the unique risk factors associated with VTE and the benefit of thromboprophylaxis is limited. Thus many women will be advised to have prophylactic treatment if they deliver in hospital, and Bennett-Day (2011) questions the value of this. The reader is advised to read her article for further detail.
Risk assessment for venous thromboembolism (VTE) (RCOG 2015)
|Pre-existing risk factors||Tick||Score|
|Previous VTE (excluding single event related to major surgery)||4|
|Previous VTE – provoked by major surgery||3|
|Known thrombophilia (high risk)||3|
|Medical comorbidities, e.g. sickle cell disease, current intravenous drug user||3|
|Family history of VTE – unprovoked or estrogen related||1|
|Known thrombophilia (low risk, no VTE)||1|
|Age (>35 years)||1|
|Gross varicose veins||1|
|Obstetric risk factors|
|Pre-eclampsia (current pregnancy)||1|
|In vitro fertilization/assisted reproductive technology use first trimester||1|
|Caesarean section in labour||2|
|Elective caesarean section||1|
|Mid-cavity or rotational forceps||1|
|Prolonged labour (>24 hours)||1|
|Postpartum haemorrhage (>1 L or transfusion)||1|
|Preterm birth (current pregnancy)||1|
|Stillbirth (current pregnancy)||1|
|Transient risk factors|
|Surgical procedure in pregnancy or ≤6 weeks postpartum excluding perineal repair post-delivery||3|
|Ovarian hyperstimulation syndrome (first trimester)||4|
|Current systemic infection||1|
|If total score ≥4 antenatally – consider thromboprophylaxis from first trimester|
|If total score ≥3 antenatally – consider thromboprophylaxis from second trimester|
|If total score ≥2 postnatally – consider thromboprophylaxis for at least 10 days|
|If admitted to hospital antenatally, prolonged admission (≥3 days) or readmission during the puerperium – consider thromboprophylaxis|