I think they are not inputs from maternal placenta. I think they are the results of foetus metabolism. However, I do not understand it how and where exactly.
What are the roles of creatine and bilirubin in foetus circulation?
Creatine is an important energy source for body, especially for the muscles, so it is no wonder you can finde it there. I don't think it has a special role besides that. See the Wikipedia article for more information.
For bilirubin this is different, this substance is a breakdown product of the heme metabolism (basically hemoglobine). It is not water soluble and needs to be conjugated to a carrier protein (albumin). In this way it is transported to the liver, where the glucuronyltransferase conjugates it to glucuronic acid. This step makes the bilirubin water soluble and it can be excreted from the body.
Newborns have a higher bilirubin level, since their glucuronyltransferase activity is at about 0.1% of that of adults. This can lead to the typical newborn jaundice. For more details about bilirubin, see here.