Mirror Syndrome is a rare disorder affecting pregnant women and their babies - it was first described in 1892.

Mirror Syndrome, also known as Ballantyne Syndrome or triple edema. Mirror syndrome happens when the fetus has an abnormal buildup of fluid, while the mother has preeclampsia, a condition of high blood pressure.
It is often called Mirror Syndrome because of the similarity in symptoms between the mother and baby."

University of Pittsburgh Schools of the Health Sciences

Although Mirror Syndrome is known to be associated with immunological disorders, fetal infections, metabolic disorders, and fetal malformations, the biological mechanism(s) which lead to a diseased state are as yet unknown.

Further info. Wikipedia