F_ and myself had previously come across something that said that the baby was able to wee and we were wondering yesterday how much wee a roughly 2 pound baby would be producing in the womb. As it happened I stocked up on pregnancy magazines in the supermarket later in the day and one of them contained the rather startling figure that the baby produces a pint of urine a day! How does that work then - is the baby just swimming around in wee we asked each other...
Intriged by this I did what any self-respecting librarian does and Googled it :)
Turns out that amniotic fluid is a lovely stew of skin cells and wee which the baby both 'breathes' into her lungs and also drinks and wees back out again - yum! It must be noted that the wee isn't exactly the same as she will produce in the outside world - most of the waste products actually pass back over the placenta and are filtered out by the mothers circulation system through the kidneys, until the end of the pregnancy when the baby's intestines start working and she saves up the waste products for that all important first toxic poop!
Lots more info on what is going on at different times in the pregnancy can be found here.