If you are immune, it will be fine. You can have a blood test to double check.
You cannot have the vaccine if you are pg. If you were not immune and your ds had it, you would be given the immunoglobin to reduce risk. Risks are highest in the first 20 weeks, but even then are low.
Incubation period is 2-3 weeks maximum, so even if your ds gets it, he would be over it and no longer infectious by the time baby is born.
Hth.