Where does
a baby's poop
go in the womb?

The full narration of the video.

A baby inside the womb: where does its poop go? Here's the strange part: in there, the baby pees for months on end. But the poop? It holds it in. Let's follow one sip the baby swallows, all the way through.

The baby floats in a big pool of water. It's called amniotic fluid. From around the third or fourth month, the tiny kidneys start making urine. It goes straight into that pool. Near birth, the baby pees more than 500 millilitres a day. About a bottle of water.

So is the baby soaking in its own pee? Don't worry. The baby also gulps that water down. Swallow it, pee it out again. So the pool keeps moving and keeps getting renewed. And this pee is very weak. Most of the real waste has already left by another route. More on that soon.

Follow the sip down. Floating in it are flakes of the baby's skin. And fine, soft baby hair. The gut soaks up the water, but the skin flakes and hair stay behind. Add green bile sent down from the liver, and old cells the gut sheds from its own lining.

From about week twelve, all of this slowly piles up in the gut. It becomes a dark green mass, sticky like tar. With almost no smell. It has a name: meconium, the baby's first poop. The baby doesn't push it out. It just stays in the gut, for months.

Doctors usually explain it like this: the gut pushes very slowly, and the little door at the exit stays shut. Then where does the baby's real waste go? The baby doesn't eat with its mouth. Food comes in through the umbilical cord. The leftover waste rides the cord back to the placenta. And it's handed to the mother's blood.

In the end, the mother's kidneys turn it into her urine. So a pregnant mother is really going to the bathroom for two. So when does the meconium come out? After birth.

Most babies pass their first dark green poop within a day or two of birth. After a few days of milk, it slowly turns yellow. Some babies can't wait. Among full-term births, about one or two in ten pass it before they're born. It's more common past the due date. Then doctors keep a closer eye, and most of these babies are fine.

So the poop didn't go anywhere. The baby has been saving it, all the way until the day it's born. Your baby's first dark green poop: which day after birth did it arrive?