How does the fetus excrete metabolic waste?

The placenta works with both mother and baby to provide blood, nutrients and oxygen to the fetus while in the womb.

The placenta basically functions like this: Mom's blood flows into the blood lake on her side of the placenta, which bathes the chorionic villi that are threaded through with fetal blood vessels.

The metabolic waste found in fetuses is excreted through the umbilical cord back to the mother. Some of it goes to the amniotic fluid which can be seen when the baby is born.