Unreal.  Us at the level of biochemical processes.

Maternal-fetal conflict has its origins with the very first placental mammals millions of years ago. Over evolutionary time, the fetus has evolved to manipulate the mother's physiology and increase the transfer of resources like nutrition and heat to the developing child. The mother's body in turn has evolved countermeasures to prevent excessive resource flow.

Things get even more intriguing when fetal cells cross the placenta and enter the mother's bloodstream. Like stem cells, fetal cells are pluripotent, which means they can grow into many kinds of tissue. Once in the mother's blood, these cells circulate in the body and lodge themselves in tissue. They then use chemical cues from neighboring cells to grow into the same stuff as the surrounding tissue, Boddy says.

It's literally another life form taking over. 

Microchimerism can get especially complex when a mother has multiple pregnancies. The mother's body accumulates cells from each baby—and potentially functions as a reservoir, transferring cells from the older sibling into the younger one and forming more elaborate microchimeras. The presence of fetal cells in the mother’s body could even regulate how soon she can get pregnant again.

Sibling rivalry?