I always thought pregnancy was a parasitic state because the mother feeds and nourishes the fetus until birth occurs, a rather one-way relationship.  There is evidence that the fetus may be reciprocating, especially if mom has a medical illness or weakness.

The research determining the relationship between mom and fetus was inspired when it was noted that  peripartum cardiomyopathy (cardiac failure during pregnancy) has the highest recovery rate of all the cardiac diseases causing cardiac failure.  It was surmised there was something coming from the fetus that was ensuring the mother’s survival and optimal health.

There are several conditions where male cells are noticed in women with diseases such as systemic sclerosis, hepatitis, thyroid disease and cervical cancer. Male cells are not produced in women and can only come from a male fetus or transplanted tissue.

A research project using mice was developed to demonstrate this fetal phenomena.  Specially bred male mice had proteins that were visible with fluoroscopy.  The female mice did not have this protein.  When the fluoroscopically tagged male mice were mated with the female mice, and the female mice were made to have a heart attack on day 12 of their pregnancy, the fluoroscopically labeled proteins were found repairing the cardiac injury. They could only have come from the fetus. (Kara et al, A Mouse Model for Fetal Maternal Stem Cell Transfer During Ischemic Cardiac Injury, Clin Transl Sci 5(4), Aug 12: 321-328)

Perhaps this is the reason the teachers at the recent October Salt Lake City stem cell seminar commented that for each birth, a mother lives 1/3 year longer because of the donated fetal stem cells.