MMR Vaccine During Pregnancy

Should You Worry If You Got the MMR Vaccine After Conceiving?

Pregnant woman getting shot
What happens if you get the MMR vaccine while you are pregant?. Universal Images Group/Getty Images

Acquiring rubella (German measles) during pregnancy can cause miscarriage and other major problems, so women are encouraged to stay up to date on MMR (measles, mumps, and rubella) vaccinations as a way to decrease the risks. But if you accidentally got an MMR vaccination during pregnancy, should you worry? 

Why a Rubella Infection During Pregnancy Is Risky

It's especially important for women of childbearing age to get the MMR vaccination.

Infection with the rubella virus, which can cause mild flu-like symptoms and rash in both children and adults, generally isn't serious. It's also extremely rare in the U.S., thanks to childhood vaccinations (the rubella vaccine has been available since 1969 and the MMR vaccine has been available since 1971). However, if an expectant mother contracts it and passes it to her developing baby in the womb, it can cause very serious harm to the fetus. 

Possible pregnancy risks that are related to a rubella infection (not the rubella vaccination) include:

  • Birth defects (congenital rubella syndrome): The risk of a baby developing congenital rubella syndrome depends on when in the pregnancy the mother contracts the infection. During the first trimester, the risk is close to 85 percent. Infection between the 13th and 16th week of pregnancy leads to congenital rubella syndrome in around 54 percent of babies. The risk drops to 25 percent later in the second trimester, and third-trimester infections rarely lead to congenital birth defects.  The syndrome often includes blindness, hearing loss, heart defects, microcephaly (a small head), and mental retardation.

Even though rubella is rare now, doctors usually test all women to see if they have immunity to the infection at the time of the first prenatal visit.

How Doctors Prefer to Time the MMR Vaccine

The MMR vaccine is designed to provide protection against rubella, rubeola (measles), and mumps.

It is prepared with weakened (attenuated) live viruses (in contrast to many vaccines that are prepared with killed viruses), so doctors usually advise avoiding pregnancy for at least one month after receiving the vaccine to reduce the risk of becoming infected.

However, sometimes women might not be aware that they are pregnant when they are vaccinated. Others might accidentally get pregnant sooner than one month after receiving the MMR vaccine.

What Research Shows

In studies looking at MMR vaccination during pregnancy, researchers found:

  • None of the subjects gave birth to a baby with congenital rubella syndrome. 
  • Miscarriage rates were not higher than they were in the general population. 

Researchers concluded that the rubella vaccination does not seem to be risky in early pregnancy. Erring on the side of caution, though, doctors continue to advise waiting a bit to get pregnant, and they recommend against vaccinating women who are known to be pregnant.

If You Received the Rubella Vaccine During Pregnancy

If you received the MMR vaccine during your pregnancy, try not to panic. The advice regarding waiting to get pregnant after a rubella vaccination is based on a theoretical risk, rather than on a documented evidence of risk.

Chances are, everything will be fine. Still, be sure to mention it to your OB/GYN in case he or she wants to monitor you—just to safe.

Who Should Get the MMR Vaccine?

According to the Centers for Disease Control and Prevention (CDC), all adults born in 1957 or later should have at least one MMR shot unless:

  • Lab tests show that they are immune to all three diseases (measles, mumps, and rubella)
  • The immunization is medically contraindicated for them (for instance, maybe they are allergic to one of the components)

Ideally, When to Get Vaccinated

If you're thinking about getting pregnant or you're already pregnant, here's what you need to know about getting vaccinated against MMR.

  • If you're planning a pregnancy: If you are planning on becoming pregnant soon and you haven't yet gotten the MMR vaccine (or if you don't know whether you've gotten it in the past), you can be tested for immunity. You're probably immune if you had the shot or were infected with rubella in the past. If you're not immune, get the MMR shot and then wait a month before trying to conceive. If you are immune, you can start trying to conceive immediately.
  • If you're pregnant: If you received the MMR vaccine before you got pregnant, then you're immune and you don't have to worry about contracting rubella. If you received the MMR vaccine during your pregnancy, again, it's no reason to panic, but let your doctor know in case he or she wants to monitor you. If you haven't ever gotten the MMR vaccine, get the shot shortly after you give birth. Some doctors recommend getting the vaccination before leaving the hospital and others recommend getting it at a postpartum visit. This will help keep you from getting sick and passing the infection to your baby and it will help protect your future pregnancies.

Sources:

de Martino, M. Dismantling the Taboo against Vaccines in Pregnancy. International Journal of Molecular Sciences. 2016. 17(6).pii: ​E894.

Hisano, M., Kato, T., Inoue, E., Sago, J., and K. Yamaguchi. Evaluation of Measles-Rubella Vaccination for Mothers in Early Puerperal Phase. Vaccine. 2016. 34(9):1208-14.

Keller-Stanislawski, B., Englund, J., Kang, G. et al. Safety of Immunization During Pregnancy: A Review of the Evidence of Selected Inactivated and Live Attenuated Vaccines. Vaccine. 2014. 32(52):7057-64.

Continue Reading