The diagnosis of PE during pregnancy imposes special challenges. Both CTPA and VQ scanning expose the mother and the fetus to radiation, with the fetus being particularly susceptible. The International Commission on Radiological Protection (ICRP) has made recommendations regarding the minimization of radiation exposure to both patient and fetus and many countries have introduced legislation to this end. In general terms, the fetal dose is much higher with VQ scanning than with CTPA (depending on the protocol up to 200 times higher) (700 - 800 Gy, vs 3 - 131 μGy) while the maternal dose is typically lower with VQ scanning (1.4 mSv versus 2.2 - 6.0 mSv).

This fetal dose advantage for CTPA even applies to protocols specifically modified for pregnant patients like half-dose perfusion scans (140 - 250 μGy). Other considerations are the somewhat higher risk for the mother to develop breast cancer with CTPA and the lack of human safety data for the effects of iodinated contrast media on the fetus, although they approved to be safe in animal experiments. Therefore, any search for PE in a pregnant patient should involve a thorough discussion of the risks and benefits with the patient. If imaging is necessary with ionizing radiation, the currently available data support the preferential use of CTPA, if possible with a modified low-dose technique and limited anatomical coverage. Automated tube modulation should be used for all scans, regardless if the patient is pregnant or not. However, as a first step, an ultrasound of the legs is recommended as a surrogate test for pulmonary embolism.

The D-dimer concentration is usually increased in the second and third trimester of the pregnancy and normalizes 4 to 6 weeks after delivery. Thus, the test is clearly less useful during pregnancy. As significant controversy exists on this topic and because no study has ever validated a negative D-dimer test for t he exclusion of PE in pregnancy, the use D-dimer testing as a stand-alone test to exclude a PE can currently not be recommended in this setting.