Fetus is not a transplant in the body of the mother. Food you ingest does not go inside the body. It remains out side the body. like wise the fetus is not inside the body. It is outside the body of the mother. The proteins from the fetus do not come in direct contact of the mother. There is placental barrier between the fetus and the mother.

The possessive form of fetus is fetus' or fetus's

The amniotic sac and amniotic fluid inside the womb.

Fetal calf, fetus, fetus calf, or cow fetus.

A female fetus with an a y chromosome is what makes it develop differently from a male fetus.