We concluded during one of our sessions that the risk of PE in pregnancy is mainly raised towards the end, and despite the likelihood of pregnancy causing a raised d-dimer, a negative result was still a negative result, and could be used to rule out PE in early pregnancy.
This has been supported by this systematic review, which concluded that a negative d-dimer and low-moderate risk Well's score appears adequately sensitive to rule out PE in the first two trimesters of pregnancy. The likelihood of having a normal d-dimer level in later pregnancy is slim even in the absence of thromboembolism (quoted as 0-1%), making it fairly useless as a diagnostic test.
There is a consistent finding in all of the studies that D-dimer values are raised in pregnancy. It could therefore be extrapolated that current D-dimer levels would be more sensitive in pregnant women than in non-pregnant women as they are more likely to already have higher D-dimers. A negative D-dimer in this group would be highly suggestive that the patient does not have a PE unless there is strong clinical suspicion.