Obviously, this clinical circumstance would never present itself. The pregnant patient is going to be the young female patient… who says that she’s pregnant. Although, the incidence of cryptogenic pregnancy is often underestimated, and has been shown to be around 1/475.1 Cryptogenic pregnancies that are discovered at the time of delivery have an incidence of approximately 1/2500.1
The AAA patient would be the older patient, often times with risk factors for vascular disease: smoking, diabetes mellitus, hypertension and hypercholesterolemia.2 The prevalence of AAA goes up with age. It has a very low incidence during child bearing age. Here’s a chart from reference two.
Jenkins A, Millar S, Robins J. Denial of pregnancy: a literature review and discussion of ethical and legal issues. J R Soc Med. 2011;104(7):286-91. [PDF]
Lederle FA. Ultrasonographic screening for abdominal aortic aneurysms. Ann Intern Med. 2003;139:(6)516-22. [pubmed]