The most important vaccine that you should get prior to pregnancy is the MMR (measles, mumps, rubella) vaccine. Many people received this vaccine during their childhood; however, immunity can wane over time. Your doctor can order a blood test called a titer that looks at your immunity to those diseases and will decide based on your antibody levels whether you should get the vaccine again. Historically, congenital rubella syndrome was a devastating disease that affected newborns whose mothers developed rubella in the first trimester. Thankfully, because of the vaccine, this condition is now rare with fewer than 1,000 cases a year but even those are preventable.