Also tell your health care professional if you are allergic to any other substances, such as preservatives. Tell your doctor if you are pregnant or if you may become pregnant within 3 months after receiving this vaccine. Although adequate studies have not been done in either humans or animals and problems have not been shown to occur, use of measles, mumps, and rubella vaccine during pregnancy, or becoming pregnant within 3 months after receiving the measles, mumps, and rubella vaccine, is not recommended. Because the natural measles infection has been shown to increase the chance of birth defects and other problems, it is thought that the live virus vaccine may cause similar problems. Mumps vaccine may infect the placenta, although the vaccine has not been shown to infect the fetus or to cause birth defects.
Rubella vaccine crosses the placenta.
However, the Centers for Disease Control observed more than 200 women who received the vaccine within 3 months before or after becoming pregnant and those women gave birth to normal babies. Mothers who are receiving measles, mumps, and rubella vaccine and who wish to breast-feed should discuss this with their doctors, because rubella vaccine virus may pass into the breast milk and may cause mild rubella infection in nursing babies. However, studies have not shown that this infection causes any serious problems. Use is not recommended for infants younger than 12 months of age, unless the risk of measles infection is high. Waiting until children are at least 12 months of age is important because antibodies that infants receive from their mothers before birth may interfere with the effectiveness of the vaccine.