Is alagille syndrome autosomal dominant? can it be detected in utero?

Yes it is : It is autosomal dominant. It would be difficult to detect but if a parent had it then your doctor would be very suspicious about it. It is possible to do a amniocentesis and then a very special dna test on that fluid, but it would require a special lab to do the test, it is not in the routine.

Yes: It's quite variable in its expression. You should be able to get a test before birth.