My niece had that while I was in my first trimester. My OBGYN did blood work and it showed that I had the antibodies(so I had already been exposed in the past) for it already, so I didn't have to worry about it. If I remember correctly from back when I was reading about it, many people already have the antibodies from prior exposure, so hopefully you already have them and won't have to worry!
ETA: This article may ease your mind....
http://www.cdc.gov/parvovirusb19/pregnancy.html