18 week fetal us indicated enlarged bladder. kidneys measured normal. amniotic fluid normal. any advice?

Here are some ...: The finding of "enlarged" bladder for a fetus of 18 weeks shouldn't rouse an overly concern at all. Clinically, this finding may just present a normally distended bladder before peeing. So, stop worrying about it and see what it may be in follow-up US as long as you're clinically sound for normal pregnancy. In fact, nothing could be done anyway even if something is serious. So, seek pro-counseling

Full bladder US?: If the ultrasound was done with a full bladder as is usually done, then the pregnancy will distort and displace the bladder at 18 weeks, so it is difficult to say that the "bladder was enlarged". Since the amniotic fluid content is OK. as well as the fetus then "no worries" at this juncture.