i just found out my friends child has slap cheek, whom my son and i see regaurly. im pregnant 20 weeks, the doctor is doing the blood test but i have been reading about it to find out what it may do to the baby. it can effect the baby up to 20 weeks pregnant. it can cause miscarrage, heart problems in baby and low iron, where baby needs blood transfetion in uterus. it is a big deal, get the blood test. if you have been in contact with some one who has it with in the last 4 to 20 days.