Hi,
I used to work in a hospital laboratory so I know a little about this.
I'm not completely sure about the differences in pregnancy but this is what I know.
Bilirubin in urine is used as an indicator of disease in the liver and/or red blood cells, but this is very dependant on what the concentration is and what the other symptoms are (eg yellowing of whites of the eyes). Bilirubin can also be an indicator of something as simple as a UTI which is easily treated, even in pregnancy.
I know that pregnancy puts a lot more pressure on all organs of our bodies so maybe your liver is just having to work a bit harder. My guess is probably that your levels of bilirubin are not high enough to cause concern (otherwise they would have said something to you?), they are probably just slightly elevated and so they have made a note of it so they can monitor it as your pregnancy progresses.
I hope this helps, but I would suggest if you are still worried about it, that you should mention it to your doctor or midwife when you next see them.
