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How does the placenta remove carbon dioxide and other wastes from the fetus?

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human fetus; prenatal development — prenatal development An ultrasound image of a human fetus.

The placenta facilitates the removal of waste products from the fetus through a process of diffusive interchange between the fetal and maternal bloodstreams.12

Within the placenta, the fetus is connected to the organ via the umbilical cord, which contains blood vessels that transport fetal blood to the chorionic villi. These villi are bathed in maternal blood within the intervillous space, but the two circulations remain physically separate, divided by a thin barrier consisting of the trophoblastic covering, connective tissue, and capillary walls.12

Because the partial pressure of carbon dioxide and the concentration of nitrogenous wastes are higher in the fetal blood than in the maternal blood, these substances diffuse out of the fetal capillaries and into the maternal circulation. Once the fetal blood is purified and enriched with nutrients and oxygen from the mother, it is collected into fetal veins and returned to the fetus through the umbilical vein, completing the circuit.1