Pregnancy, particularly late pregnancy is a significant risk factor (4 times relative risk) for the development of venous thromboembolism. D-Dimer levels are often elevated in pregnancy which limits its use as a triage tool. Although a negative D-Dimer in a low risk patient in early pregnancy may be considered helpful, use of D-Dimer to exclude PEs is not supported by the Royal College of Obstetricians and Gynaecologists.
Investigation strategies in pregnant patients frequently advocate bilateral leg vein ultrasonography initially in order to minimise ionising radiation exposure. The pick up rate for this investigation is very low however and a need to progress to further imaging is frequently required.
Although the total radiation doses with V/Q and CTPA are small, a CTPA gives a larger dose of radiation to maternal breast tissue than V/Q whereas V/Q gives a larger dose of radiation to the foetus. Women with suspected PE should be advised that V/Q scanning carries a slightly increased risk of childhood cancer compared with CTPA (1/280,000 versus less than 1/1,000,000) but carries a lower risk of maternal breast cancer (lifetime risk increased by up to 13.6% with CTPA, background risk of 1/200 for study population).
Some centres advocate a half dose perfusion scan as a first test although this can sometimes lead to a further test (CTPA) being needed if the scan is indeterminate resulting in the patient receiving a larger radiation dose overall..
Emergency Medicine physicians should be able to explain the level of risk to mother and foetus of investigations that they may request from the ED since these questions are frequently asked.