Your guide to having tests for suspected pulmonary embolism during pregnancy
Who needs this leaflet?
You need this information if you are pregnant and doctors have advised that you need diagnostic tests to look for pulmonary embolism.
What is Pulmonary Embolism?
Abnormal blood clots can sometimes form in veins, usually in the legs. Clots can then travel through the circulation, and become stuck in arteries in the lungs. Symptoms could include shortness of breath, chest pain, coughing up blood, or sudden collapse. Pulmonary embolism can be fatal and is a leading cause of death in pregnancy. About 1 in 100,000 pregnant people in UK will have a fatal pulmonary embolism.
Why are diagnostic tests needed?
The symptoms of pulmonary embolism could be due to many other conditions that affect the lungs or heart.
It is important to identify people who definitely need the treatment for pulmonary embolism to prevent more clots from forming.
Each year in the UK, it is estimated that around 4,000 pregnant people have diagnostic tests for pulmonary embolism, but less than 400 have positive tests and need treatment.
Which diagnostic tests are used?
Royal College of Obstetricians and Gynaecologists guidelinesadvise that all pregnant people with suspected pulmonary embolism should have an X-ray of the chest and an electrocardiogram, and in most cases a decision will then be made to recommend one of the following:
• Nuclear medicine (NM) lung scan – which involves an injection, and probably also inhalation, of small amounts of radioactive substances with detailed pictures of the lungs created using a specialised machine called a “Gamma Camera”.
• Computed Tomography (CT) lung scan – which involves an injection of dye with detailed X-ray images of the lungs created by the CT scanner.
In practice, the NM lung scan is unlikely to be helpful if X-ray of chest is abnormal.
Occasionally, if one test is inconclusive, it may be necessary to do the other one.
How might radiation affect the pregnant person?
With both tests, there is a small increase in the risk of pregnant patients developing breast cancer over the course of their life.
With the NM lung scan, the risk increases by 0.01%.
With the CT lung scan, the risk increases by 0.1%.
However, in either case, women have a 12.5% risk of developing breast cancer over the next 50 years WITHOUT having had the test.
Is there anything I should tell the staff before the scan?
Yes. If you are breastfeeding, please inform us as you will need to refrain from breastfeeding for several hours following the scan.
How might radiation affect the baby during the pregnancy?
With both tests there is a small increase in the risk of the baby developing cancer in childhood.
With the NM lung scan, the risk increases by 0.002%.
With the CT lung scan the risk increases by 0.004%.
However, in either case, the baby has a 0.2% risk of developing cancer in the next 15years WITHOUT having had the test.
What treatment would be needed?
The treatment is with daily injections of a blood thinning agent and in pregnancy this carries a small risk of bleeding (2%) for example nose bleeds, etc. It is important to note that this blood thinning agent does not affect your baby and carries no risk of miscarriage.
The blood thinning agent also carries a small risk (1.8%) of a skin reaction.
Are there any other concerns about the baby?
There is a very small theoretical risk that the dye used for the CT lung scan could affect the baby’s thyroid.
As a precaution, guidelines adopted by the Royal College of Radiologists advise that babies born to people who received dye while pregnant should have testing for underactive thyroid. In England, this is performed in all newborn babies by a heel prick test as part of routine screening.
If you have symptoms of pulmonary embolism during pregnancy, it is important to have diagnostic tests to check whether treatment with blood thinners is necessary.
Diagnostic tests involve medical radiation, but the extra risk of developing cancer is very small, for both the pregnant person and the baby.
Most cases will have X-ray of chest and a Nuclear Medicine (NM) lung scan.
If a NM lung scan is not possible, then a Computed Tomography (CT) lung scan will be offered instead.
- MBRRACE-UK (2017) Saving Lives, Improving Mothers’ Care
- Armstrong et al (2017) Clinical Radiology 72:696 Survey of UK imaging practice for the investigation of pulmonary embolism in pregnancy
- Greer et al (2005) Blood 106(2):40 Low molecular-weight heparins for thromboprophylaxis and treatment of venous thromboembolism in pregnancy: a systematic review of safety and efficacy.
- Forestier et al (1984) Thromb Res. 34(6):557-60 Low molecular weight heparin does not cross the placenta during the second trimester of pregnancy study by direct fetal blood sampling under untrasound
- RCOG (2015) Green Top Guideline 37b Thromboembolic Disease in Pregnancy and the Puerperium: Acute Management
- Schembri GP, Miller AE, Smart R. Radiation dosimetry and safety issues in the investigation of pulmonary embolism. Semin Nucl Med 2010;40:442–54.
- International Commission on Radiological Protection. Pregnancy and medical radiation. ICRP Publication 84. Ann ICRP 2000;30(1)
- Remy-Jardin M, Remy J. Spiral CT angiography of the pulmonary circulation. Radiology 1999;212:615–36
- HPA document RCE-9 “Protection of Pregnant Patients during Diagnostic Medical Exposures to Ionising Radiation” (2009)
- RANZCR (2016) Iodinated Contrast Media Guideline (subsequently adopted by UK Royal College of Radiologists).
- Atwell TD, Lteif AN, Brown DL et al. Neonatal thyroid function after administration of IV iodinated contrast agent to 21 pregnant patients. Am J Roentgenol 2008, 191: 268-71.
- Rajaram S, Exley CE, Fairlie F et al. Effect of antenatal iodinated contrast agent on neonatal thyroid function. Br J Radiol 2012, 85: e238-42.
- Kochi MH, Kaloudis EV, Ahmed W et al. Effect of in utero exposure of iodinated intravenous contrast on neonatal thyroid function. J Comput Assist Tomogr 2012, 36: 165-9.