I nused Audrey while I was pg with Sammie and had no problems either. You should ask your nurse how moms become tandem nursers if they must wean while pg
I think it should be a personal choice. The isn't any info that says nursing will cause any problems but it's something that you should decided to do or not based on your personal situation.
You might also want to read
Adventures in Tandem Nursing - it talks alot about nursing while pg.