Roseola and Fifths

I got exposed to both sometime in the last two weeks, so I have to take a blood test to see if I am immune or if I contracted it recently. There is a small risk if I have never had them, and I catch them now, it could hurt the baby. They said that there is a tiny risk that it could decrease the baby's ability to produce red blood cells and require a blood transfusion in utero. I take the test in the morning.