Personally I would not get it, unless you were at an extreme high risk of contracting rubella.
I take it that you weren't vaccinated against rubella as a child?
What do you suppose the chances are that you would contract rubella, while pregnant.
Then, if you eat right, and take care of yourself, your immune system might even protect you from contracting the disease.
It is entirely up to you, but I would not say the vaccine is safe.
Ask for an insert, and read the ingredients and side effects.