I was reading this website saying that fetuses urinate into the amniotic fluid. It also mentioned that, because we drink the amniotic fluid, we’ve been drinking our urine for months.

However, why do we produce urine as fetuses? I always believed the placenta was our source of waste removal; then why have fetuses the need for filtering their blood through their own kidneys?

In addition, why would fetuses drink the amniotic fluid? Is there a benefit for doing that?