I just gets re-absorbed When I had an ultrasound with DS they were concerned about the size of his bladder, so I had to go away for a bit then come back. When they looked again it was smaller, so the conclusion was that he just had to do a wee!! Of course I had to ask about it & the sonographer just said that their wee is essential any amniotic fluid they have swallowed & it just stays in the waters. You were right in one aspect, they don't poo until they are born