Why is it dangerous to have air forced into the vagina when you're pregnant, but fine when you're not?

Air Embolism: Air entering the vagina under pressure could pass through the cervix and into the uterus. This could cause problems such as an infection (it brings bacteria with it from the vagina) or air embolism (air enters the bloodstream through the dilated vessels of the uterus). Air bubbles in the bloodstream could cause death, though this is rare. These problems are possible in non-pregnant women also.