What is the safe titre for rubella in a pregnant woman?

Q: If a pregnant woman is exposed to a person infected with rubella then what is the safe titre for rubella?

A:If a pregnant woman is exposed to rubella virus, a sample should be taken within 10 days. If the date of exposure is not known, it is recommended to take a second sample 2 weeks later. A reactive result (>or= 10 IU/ml) indicates prior or current exposure to rubella virus infection. A subject having an anti-rubella IgG titre more than 20 IU/ml is considered to be immunologically protected.