I had the same at my 8 week blood test. It said that < 10 is not immune, 10-40 requires a booster and > 40 is immune. I was 20. My sister was the same. It just means the Rubella shot we were given at school wasnt that strong. It doesnt mean theres anything wrong with you at all. Just means that after bubs is born you'll need to have a booster (you cant have it while youre pregnant). And in the mean time if you know anyone with the Rubella/Measles, just stay away from them.. but its really nothing to be too concerned over, none of my doctors or midwives said its anything to worry about.. youll be right