The assessment of venous thromboembolism risks associated with pregnancy and the postnatal period

This investigation was carried out by the Healthcare Safety Investigation Branch (HSIB). Find out more about HSIB legacy.

This investigation explores the issues associated with the assessment of risk factors for venous thrombosis in pregnancy and the first 6 weeks after birth.

Venous thrombosis occurs when a blood clot forms and causes a blockage in a person’s vein. This can lead to venous thromboembolism (VTE), when part of the clot breaks off and travels through the bloodstream, blocking a blood vessel elsewhere in the body.

Pregnant women and pregnant people are at greater risk of developing a venous thrombosis than those who are of the same age and not pregnant. Venous thrombosis related to pregnancy can occur at any stage of pregnancy and for 6 weeks after birth. Because of the increased risk, healthcare staff assess a pregnant woman’s and pregnant person’s risk factors for VTE at key stages before and after the birth so that they can be given preventative treatment if necessary.

While rare, in the UK venous thrombosis and VTE is the leading direct cause of death of pregnant women and pregnant people during pregnancy or up to 6 weeks after the end of pregnancy. Pregnant women and pregnant people who develop a VTE must undergo additional treatment and this can cause distress and anxiety at a time when they may already feel vulnerable.

This investigation uses a real patient safety incident, referred to as the ‘reference event’, to explore factors that can impact on the way staff assess a pregnant woman’s and pregnant person’s risk of VTE. It aims to support ongoing national work in this area.

At the time of the reference event, Alice was 26 years old and was pregnant with her second child. A VTE risk assessment was completed for Alice at her first antenatal appointment, when she was admitted to hospital for the birth of her child, and 24 hours after admission. Her score was zero each time, meaning no risk factors were identified for VTE. During her pregnancy Alice reported experiencing some pain in her calf; she was examined by a doctor who referred her for a scan. This ruled out a deep vein thrombosis (DVT).

Alice had her baby by emergency caesarean birth and in line with national guidance her VTE risk assessment was repeated. This indicated that a preventative dose of a blood-thinning medication would be required. Alice was started on a daily injection of low-molecular-weight heparin and was discharged from hospital.

Eleven days after the birth of her baby, Alice was taken by ambulance to the emergency department with chest pain, shortness of breath and leg cramps. She was diagnosed with a pulmonary embolism (PE) and was started on a treatment dose of blood-thinning injections. Following investigation, it was found that Alice may not have received an appropriate preventative dose of low-molecular-weight heparin to help prevent the VTE.

The investigation found that the evidence about risk factors and the occurrence of VTE in pregnancy and the first 6 weeks after giving birth is imprecise. In addition, while there are recommendations for prescribing of medication to thin the blood if a pregnant woman/pregnant person is identified as being at risk, the preventative and treatment dose(s) have not been formally tested in clinical trials.

Research studies are ongoing to address identified knowledge gaps within the evidence base. Safety risks have also been reported in research literature and are reiterated in national reports which make recommendations to improve care during pregnancy and in the first 6 weeks after birth.

In view of the national work to address gaps in the current evidence base and to avoid duplicating existing work, the HSIB investigation considered that the biggest opportunity for learning was to better understand why healthcare professionals find existing risk scoring systems difficult to apply consistently in practice. As a result, HSIB launched this investigation to identify factors that limit the effectiveness of VTE risk assessment policies and identify opportunities to further improve patient safety in this area.

• For healthcare staff, carrying out a robust assessment of risk factors for VTE is challenging, particularly in the complex and busy environment of antenatal clinics, the labour ward and on postnatal wards.
• Multiple competing demands, exacerbated by distractions and interruptions, mean healthcare professionals are constantly having to balance risk and safety for the pregnant women/pregnant people they care for and are trading off the thoroughness of assessments to improve efficiency.
• Midwives are asked to complete a number of risk assessments and screening tools to assess pregnant women’s/pregnant people’s risk at their first antenatal appointment (known as the booking appointment). However, the time needed to carry out these risks assessments may not be reflected in the time allocated for appointments.
• Risk assessments and screening tools are not all designed and presented in a consistent and logical way that would aid staff in completing the task.
• Assessment of VTE risk factors should take place routinely due to body changes in pregnancy and increased risk of VTE.
• Although assessing VTE risk is important, it is a relatively rare condition and there are a number of other competing risks that may take priority.
• Staff do not always involve pregnant women and pregnant people in, or discuss with them, the assessment of their risk factors for VTE. This means pregnant women and pregnant people may not be aware of the signs and symptoms of a possible VTE.
• The importance of knowing the signs and symptoms of VTE may not be fully understood or prioritised by pregnant women and pregnant people who may have other competing concerns and questions about their antenatal and postnatal care.
• National guidance recommends that assessment of VTE risk factors should be repeated when a pregnant woman/pregnant person presents with an ‘intercurrent problem’ (a new health issue which may or may not be related to the pregnancy). However, not all healthcare professionals understand the meaning of ‘intercurrent problem’ and therefore opportunities to reassess risk factors are missed.
• There is a mix of paper-based and electronic record keeping in antenatal and postnatal care. Electronic records systems may lack interoperability and suffer from poor connectivity which limits the ability of staff to access all the data, information, and knowledge they need at the time of assessment.
• Recommendations by MBRRACE-UK (Mothers and Babies: Reducing Risk through Audits and Confidential Enquiries across the UK) for the development of a tool to make the current assessment of VTE risk factors simpler and more reproducible, have not been acted on.

The HSIB investigation identified local learning that may assist maternity healthcare providers and local maternity systems (regional groupings of maternity service providers) when considering how to support the assessment of risk factors for VTE.

It may be beneficial for individual organisations to review how their staff involve pregnant women and pregnant people in the assessment of risk factors for venous thromboembolism and to identify any barriers that may be preventing such involvement. Greater involvement of pregnant women/pregnant people may enable more robust assessments and may make it more likely that VTE risk will be identified and acted upon and enable pregnant women/pregnant people to recognise signs and symptoms sooner.

It may be beneficial for organisations to employ quality improvement tools to implement and monitor pregnant women and pregnant people self-completing risk assessment forms in advance of their appointments.

It may be beneficial if organisations review the extent to which national guidance on the assessment of risk factors for venous thromboembolism is understood and implemented across their organisations. This will help to identify whether local barriers exist and if so, which of these to address for improved implementation.