i am a midwife, and generally mum is immune if she has definately had a good dose of chickenpox previously, however some people do not and that is why they get it a second time,i dont think you should wait for a blood test, the advice i usually give to my ladies is to have a blood test soon and then one can be sure, if you were previously screened then that is ok. also it depends on when you came into contact with the person with c p because it is important to be vacinated within a set time of contact.