How does oxygen exchanges between material and detalles blood in a pregnant women???

During pregnancy, the unborn baby (fetus) depends on its mother for nourishment and oxygen. Since the fetus doesn’t breathe air, his or her blood circulates differently than it does after birth:

The placenta is the organ that develops and implants in the mother's womb (uterus) during pregnancy. The unborn baby is connected to the placenta by the umbilical cord. 

All the necessary nutrition, oxygen, and life support from the mother’s blood goes through the placenta and to the baby through blood vessels in the umbilical cord.

Waste products and carbon dioxide from the baby are sent back through the umbilical cord blood vessels and placenta to the mother's circulation to be eliminated.