Jolleigh, it's sometimes called fifth disease because it's the next common childhood rash illness after measles mumps rubella and chicken pox.
The risk is mostly prior to twenty weeks (I am 14 weeks) and it can cause complications with the baby with a 9% risk of it causing the baby to die. There are some interventions they can do to improve outcomes though so if you are exposed they test for immunity and then if you aren't immune you are tested a month later to see if you caught it. Then if you did you'd be referred to foetal medicine for monitoring.
PiratesMam, I'm on ondansetron for the sickness. I've had most things but none of them have been effective except for this and cyclizine made me more sick.
Oh and slapped cheek disease is no concern at all for DD - it's made her rather grumpy and she's sleeping more than usual but it's nothing at all to worry about for her. (And I guess a good thing for her to have now as it then avoids potential worry in pregnancy!)