Reynod :
http://www.abc.net.au/science/articles/2013/06/05/3774391.htm
Interesting article.
Oh boy, is this ever a WIDE open door for a bunch of dirty jokes. And I'll stop there.
@Riser
That paper you are discussing with morning sickness and spermatophagia sounds a little fishy. The reason there is morning sickness is due to high levels of estrogen and progesterone in the mother's bloodstream. These hormones are made by the placenta and are their levels peak during the first trimester of development when the embryo is very small. The levels decrease after that and the morning sickness gets better in the second trimester. I don't believe sperm has any known anti-nausea properties.
Morning sickness is certainly NOT due to the mother's immune system rejecting the "foreign" embryo. The very complicated placenta allows for a blood-blood barrier between maternal and embryonic/fetal circulation as various substances diffuse across the placenta. The maternal circulation does not see much of anything for fetal cells until at birth due to that indirect placental connection. Otherwise the maternal immune system would see a large number of "foreign" cells and develop antibodies to kill the "foreign" object. Antibodies do cross the placenta and would destroy the fetus. The best example I can think of that describes the whole issue of how the placenta prevents an anti-rejection mechanism and what happens if there is a rejection is with
Rh isoimmunization The first baby is fine as the mother doesn't see any "foreign" Rh+ blood cells until right when the first Rh+ baby is born, so the baby is fine. However then she makes antibodies against Rh+ after that exposure which cross the placenta and wreak havoc on subsequent Rh+ fetuses.