Why is MMR vaccine contraindicated in pregnancy?

The MMR (measles, mumps, and rubella) vaccine is contraindicated in pregnancy because it contains live attenuated viruses, which could potentially harm the developing fetus. Infection with rubella during pregnancy can lead to serious congenital defects and complications. Therefore, it is recommended that women avoid becoming pregnant for at least 28 days after receiving the vaccine to ensure safety. Pregnant women should instead receive the vaccine postpartum.