Does my baby pee and poop while still in my placenta?

Hello nunu88

First of all your baby is not in the placenta.
The placenta is a kind of interface between you and the baby.
The baby and placenta are together in the womb.

No your baby does not pee or poo in your womb. The umbilical cord takes care of supply of all that is needed, and of removal of all waste products.

:>)

The amniotic fluid is made from the baby's pee. They ingest it and practice breathing with it. At your 20 week u/s you'll probably even see your baby's bladder full. They don't usually poo until late in pregnancy. They really shouldn't, but if you go overdue there is a chance they will have the first bowel movement in utero.