MMR Vaccine During Pregnancy

Should You Worry if You Had the MMR 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 keep up-to-date on MMR vaccinations as a way to decrease the risks. But if you accidentally had an MMR vaccine (measles, mumps, and rubella) during pregnancy, should you worry? 

Rubella in Pregnancy

First, let's review why it's especially important for women of childbearing age to get the MMR (Measles, Mumps, and Rubella) vaccine.

Infection with the rubella virus, which can cause mild flu-like symptoms and rash in children and adults, generally isn't serious. It's also extremely rare in the U.S. thanks to childhood vaccinations. 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 baby: 

Possible pregnancy risk related to a rubella infection (not the shot) include:

Congenital Rubella Syndrome - The risk of a baby developing congenital rubella syndrome when a mother acquires the infection (not by receiving the shot) during pregnancy, depends on when in pregnancy she contracts the infection. During the first trimester, the risk is close to 85 percent. Infection between the 13th and 16th weeks 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 with widespread immunization (the rubella vaccine has been available since 1969 and the MMR since 1971) doctors usually test all women to see if they have immunity to the infection at the time of the first prenatal visit.

The MMR Vaccine in Pregnancy

The MMR vaccine is designed to provide protection against rubeola (measles), rubella (German measles) and mumps. It is prepared with weakened (attenuated) live viruses (in contrast to many vaccines which are prepared with killed viruses), so doctors usually advise avoiding pregnancy for at least a month after receiving the vaccine to reduce the risk of becoming infected.

Yet occasionally, 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.

If you are in this situation, try not to panic. The advice to wait to get pregnant after a rubella vaccination is based on a theoretical risk of problems to the fetus rather than documented evidence of risk

Studies on Women Who Have Received the MMR During Pregnancy

In the studies looking at accidental MMR vaccination during pregnancy:

  • None of the subjects gave birth to a baby with congenital rubella syndrome. 
  • Miscarriage rates were not higher than 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, doctors continue to advise waiting a bit to get pregnant, and they recommend against vaccinating women known to be pregnant.

    IF You Received the MMR and are Feeling Anxious

    If you found out that you were pregnant soon after receiving an MMR vaccination, there's no cause for alarm and chances are that everything will be fine. Still, be sure to mention the matter to your doctor in case he or she wants to monitor you—just to safe.

    Those who accidentally received the vaccine after conception may find some reassurance in that studies have not only found the rubella vaccine to be associated with little risk when given in pregnancy, but many other Immunizations—including both those with killed and live attenuated viruses—have failed to show significant problems when given in pregnancy. This includes vaccines for flu, tetanus, HPV, hepatitis A, rabies, yellow fever, typhoid, and the live attenuated polio vaccine.

    When Should You Be Vaccinated?

    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 they are immune to all three diseases (measles, mumps and rubella)
    • The immunization is medically contraindicated for them (they have some reason why the risks of the vaccine might outweigh the benefits, such as an allergy to one of the components)

    If you are currently pregnant and do not have immunity against rubella, studies suggest that immunization in the early postpartum period (shortly after giving birth) is safe and very effective.

    If You Are Planning a Pregnancy

    If you are planning on becoming pregnant soon and haven't been vaccinated (or don't know if you were), 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 wait a month to start trying to conceive. If you are immune, you don't have to wait!

    If you're already pregnant and aren't immune, get the shot right after you give birth. Some doctors recommend giving the vaccination before leaving the hospital and others at your postpartum visit. This will keep you from getting sick and passing the infection to your baby, and will 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.

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