Investigation of Suspected Pulmonary Embolism (PE) in Pregnancy – Risks to you and your baby

Patient Experience

  • Reference Number: HEY1050/2024
  • Departments: Maternity Services
  • Last Updated: 1 January 2024


This leaflet has been written to give you information about two different types of lung scan used within the hospital so that you are informed about the amount of radiation, and the associated risks, that you and your unborn baby will receive when you have one of these scans.

Your doctor, together with a radiologist (doctor specialising in imaging), will decide which type of scan is most appropriate for you to have. They will take into account your medical history and the stage of your pregnancy.

Thrombosis in pregnancy

A thrombosis is a blood clot in a blood vessel (a vein or an artery). Veins are the blood vessels that take blood back to the heart and lungs whereas arteries take the blood away.

Pregnancy increases your risk of thrombosis, with the highest risk being just after you have had your baby. However, venous thrombosis is still uncommon in pregnancy or in the first 6 weeks after birth, occurring in only 1 to 2 in 1000 women. Thrombosis can occur at any time during your pregnancy, including the first 3 months.

Venous thrombosis occurs in a vein. This can be serious because the blood clot may break off and travel in the bloodstream until it gets lodged in another part of the body, such as the lung. This is called a pulmonary embolism (PE) and can be life threatening. However, dying from a PE is very rare in women who are pregnant or who have just had a baby.

If your medical team suspects you may have a PE, the following tests will be performed:

  • A chest X-ray – this can also identify common problems that could be the cause of your symptoms, such as a chest infection. It uses a tiny dose of radiation that is not considered harmful for you or your baby.
  • An ECG – a tracing of your heartbeat.
  • An ultrasound scan of your legs.
  • If the leg scan is normal, your doctor may ask to have a scan of your lungs. There are two types of scan that can be performed to look at your lungs:
    • The first is called a ventilation/perfusion scan (VQ scan) and is performed in the nuclear medicine department.
    • The second type of scan is called a computed tomography (CTPA) scan and is performed in the radiology department.

Both scans involve the use of ionising radiation.

While on the ward, the doctor will discuss with you why you are having a VQ or CTPA scan and the risks and benefits of the scan (see below). The doctor will answer any questions you might have.


CTPA scan is a specialised X-ray. This scan looks at the blood vessels from the heart to the lungs and identifies any blockages in these vessels.

What preparation is required for the CTPA scan?

You may be given a gown to wear during the scan. Metal objects, such as necklaces and bra fastenings may affect the CT images and will be removed prior to the examination while you are changing.

A cannula (small plastic  tube) will be placed into a vein in your arm before you leave the ward.

Unless you have been told otherwise, you may eat and drink normally before and after the scan. If you are asthmatic and use inhalers you should bring your inhalers with you to the radiology department.

What will happen during the CTPA scan?

You will be taken into the CT scanning room where you will be asked some questions to identify you, such as your name and date of birth. The radiographer will explain the procedure to you and will check some other details such as any allergies you may have. You will be asked to lie down on the couch.

A lead apron will be wrapped around your tummy and back to help reduce the amount of radiation that reaches the baby.

The couch will be moved slowly to position your chest within the ‘polo mint’ of the scan machine. The radiographers will go into the control room but they are able to hear you talk over the intercom and they will be able to see you throughout the scan.

With modern CT machines, you will only hear slight buzzing, clicking and whirring sounds as the machine takes the images. During the scan, the couch will move in and out of the machine a few times.

You will be asked to breathe in and hold your breath for a few seconds as the couch moves through the scanner.

You will receive an injection of dye automatically through the cannula in your arm. The radiographers will tell you over the speaker before you receive the injection. When the dye enters your bloodstream during the procedure, it clearly shows the blood vessels in the lungs, making them appear bright white on the images.

When the dye is injected it is common to experience a ‘hot flush’ sensation, particularly across the neck and chest. This feeling goes away quite quickly and is normal. Many people experience the hot sensation around the rest of the body. Some people also get a metallic taste in their mouth.

The result of the scan will be available shortly after you return to the ward. Your medical team will discuss the results with you and what happens next.

VQ Lung Scan

A VQ lung scan is also known as a ventilation perfusion scan. This scan looks at the blood and air supply to your lungs. It involves breathing slightly radioactive air through a mouthpiece, an injection of a small amount of radioactive liquid and imaging with a special camera.

How do you prepare for this scan?

There is no special preparation for this scan. You can eat, drink and take medication as normal. A cannula will be placed into a vein in your arm before you leave the ward.

You do not need to undress for the examination, but you may need to remove metal objects from your clothing or upper pockets, such as jewellery or belts as these will interfere with the quality of the pictures.

How is the scan performed?

A technician will ask you to breathe slightly radioactive air through a mouthpiece for about one to two minutes. It will not make you feel any different.

You will need to lie still with your arms above your head and breathe normally while the images are taken. The first series of images will take about 20 minutes.

Next, while you are still lying on the scanning bed, a small amount of radioactive liquid will be injected into the cannula in your arm. This will not make you feel any different. More images will be taken, similar to the previous ones, but these will take approximately 10 minutes.

Alternatively, the radiologist may perform only a lung perfusion scan where half the dose of radioactive dye is used without you having to breathe the radioactive air. However if this test does not provide enough information the full VQ scan or sometimes a CTPA scan may need to be performed.

You will not be enclosed in a tunnel and the radiographers will be in the room with you at all times. Except for the minor discomfort of having the needle for the injection, the test is painless and usually takes less than an hour.

Risks from the radiation

The radioactive substances are used as sparingly as possible and the benefits of this scan far outweigh the small risk from radiation. The radiation dose you will receive is similar to the radiation that you receive from natural sources in a year. The radioactive substance is quickly eliminated from your body. You can help this process by drinking plenty of fluid for the rest of the day and passing urine more often than normal.

Can breastfeeding mothers have the test?

Breast-feeding mothers can have VQ scan but will be required to express and discard the breast milk for 12 hours after the injection. If possible you can express milk the day before and use that on the day of the test.


It is important to know if you have a blood clot in your lung. If this is not found and treated, it could lead to conditions such as pulmonary hypertension, stroke or even death.

By not having a scan, you could be treated for a blood clot when you do not need to be treated.


The request for a lung scan will be discussed with a consultant radiologist (who specialises in scans involving radiation) and the senior medical team looking after you.

They consider that:

  • The risks to you and your baby from a lung scan are very small.
  • The benefits from knowing what is wrong with you outweigh the risk.
  • You should be fully informed of all risks and benefits involved with the procedure.

Most patients will experience no adverse effects during or after the scan.

There is an extremely small chance that you might have an allergic reaction to the injection. Most reactions are mild; radiographers are trained to recognise the signs of a reaction and how to look after you. Doctors are also available should you start to feel more unwell.

A reaction may involve feelings of intense hot flushing, nausea, developing a rash or becoming breathless or wheezy. Severe reactions to the dye are extremely rare.

Both the VQ scan and CTPA scan involve the use of ionising radiation. Although the radiation doses from the examination are small, any examination that uses radiation is only performed when absolutely necessary. This means the benefit to you (and therefore also your unborn child) of having the examination outweighs the risks of not having it.

In this particular situation the risks of NOT having a lung scan are as follows:

  • You could have a blood clot in your lungs. If this is not found and treated, it could lead to conditions such as pulmonary hypertension, stroke or even death.
  • By not having a scan, you could receive unnecessary treatment for a blood clot when you do not need to be treated.

What are the radiation risks to me?

The CT and VQ scans both carry a small risk but this needs to be weighed up against the risk to you and your baby of an undiagnosed PE.

Because breast tissue is sensitive to radiation exposure in pregnancy, there is a small increased risk of breast cancer. A CTPA scan gives a higher dose of radiation to your breasts than a VQ scan and the lifetime risk of breast cancer may be increased.

For a 25 year old whose background risk of developing breast cancer in the following 10 years is 1 in 1000, the extra risk from a CTPA scan means an extra 136 women would develop breast cancer for every 1 million CTPA scans.

What are the risks to my baby?

The risks to your baby are extremely low; there is no substantial risk of causing death, malformation or impairment of mental development.

  • Ultrasound is generally safe in pregnancy.
  • The chest X-ray uses a very small dose of radiation and your baby is covered with a protective sheet, so the risk of childhood cancer is tiny.
  • The risk to your baby of developing childhood cancer after a VQ scan or a CT scan is slightly higher with a VQ scan. This risk is an extra 1 case of cancer for every 34,000 VQ scans performed. It is important to note that this risk is low compared to the baseline risk of childhood cancer in the UK of 1 in 500.

Is one test better than the other?

Although both tests can show whether there is a blood clot on your lungs, they each have advantages and disadvantages that will be taken into account when the doctor decides which test you will have.

VQ scans are often preferred during pregnancy because they give a lower radiation dose to your breast tissue (which is more sensitive than usual to radiation during pregnancy).

However, a CTPA scan will give a smaller radiation dose to your baby, and it can be more accurate in detecting blood clots in your lung. Also, it provides information on other tissues in the chest.


If your medical team suspects you may have a blood clot in your lungs, they will treat you with blood-thinning injections which you need to take once or twice daily depending on your body weight. If a VQ or CTPA scan is not performed your doctor cannot confirm or rule out a blood clot. In this case you would need to continue the daily injections throughout the pregnancy and for several weeks afterwards.

Are there any risks to my baby and me from Heparin?

Low-molecular-weight heparin does not cross the placenta and therefore cannot harm your baby.

There may be some bruising where you inject – this will usually fade in a few days.

One or two women in every 100 (1 to 2%) will have an allergic reaction. If you notice a rash after injecting, you should inform your doctor so that the type of heparin can be changed.

General Advice and Consent

Most of your questions should have been answered by this leaflet, but remember that this is only a starting point for discussion with the healthcare team.

Consent to treatment

Before any doctor, nurse or therapist examines or treats you, they must seek your consent or permission. In order to make a decision, you need to have information from health professionals about the treatment or investigation which is being offered to you. You should always ask them more questions if you do not understand or if you want more information.

The information you receive should be about your condition, the alternatives available to you, and whether it carries risks as well as the benefits. What is important is that your consent is genuine or valid. That means:

  • you must be able to give your consent
  • you must be given enough information to enable you to make a decision
  • you must be acting under your own free will and not under the strong influence of another person

During the course of your procedure the radiology staff will ask questions that may appear unnecessary to you and these may be repeated at certain intervals. Please be assured that these questions are necessary to ensure that all aspects of your care during the procedure are maintained to a high standard.

Information about you

We collect and use your information to provide you with care and treatment. As part of your care, information about you will be shared between members of a healthcare team, some of whom you may not meet. Your information may also be used to help train staff, to check the quality of our care, to manage and plan the health service, and to help with research. Wherever possible we use anonymous data.

We may pass on relevant information to other health organisations that provide you with care. All information is treated as strictly confidential and is not given to anyone who does not need it. If you have any concerns please ask your doctor, or the person caring for you.

Under the General Data Protection Regulation and the Data Protection Act 2018 we are responsible for maintaining the confidentiality of any information we hold about you. For further information visit the following page: Confidential Information about You.

If you or your carer needs information about your health and wellbeing and about your care and treatment in a different format, such as large print, braille or audio, due to disability, impairment or sensory loss, please advise a member of staff and this can be arranged.

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