OK, I've tried for 2 days to find my citation for this, but I'll try to
explain it as accurately as I can remember.  In our Healthy Pregnancy
classes, we were instructed to teach our couples about the dangers of blowing
into the vagina DURING PREGNANCY.  This is because there is a risk of air
being blown between the membranes surrounding the fetus and the uterus, where
numerous blood vessels are exposed and dilated to nourish the placenta &
baby.  There apparently have been documented cases of an air bubble finding
its way into the woman's bloodstream this way, where it acts just like a
blood clot to prevent blood from getting to the brain/lung/heart, causing
tissue damage and even death from stroke.  This risk is only during pregnancy
and the immediate postpartum period, before the uterus has had a chance to
involute.

Hope this clears up the question.  If anyone would like me to keep on looking
for the journal article that describes this, please e-mail me, & I'll check
with our other educators, whose files are hopefully more organized than mine!

Carol