I recently started telling my pregnant patients not to travel to parts of Washington state, because they might be exposed to measles. New cases of measles continue to be identified in Clark County along the southern Washington border, just outside Portland. Now, an outbreak in Vancouver, British Columbia, has Canadian health officials worried. Measles outbreaks are currently ongoing in 11 U.S. states, but the outbreak in Washington state is one of the largest.

As a disease, measles is not simply a rash and a fever. Measles is one of the most contagious viruses that we know, and it can be deadly. In fact, the World Health Organization estimated that 110,000 people died of measles in 2017.

Babies and pregnant women are extremely susceptible to measles and its most severe complications. The most concerning for pregnant women are severe breathing problems and brain damage. A pregnant woman can also lose a pregnancy to miscarriage or stillbirth due to measles. The infection can also cause preterm birth, which can lead to serious lifelong health problems for the baby.

As an obstetrician who has spent her career protecting pregnant women and fetuses from complications in pregnancy, I understand parents’ desire to do what is best for their children. The anxiety around the safety of vaccines is based on a now debunked “scientific” article. Some of the clearest evidence supporting the safety of the measles, mumps and rubella vaccine came  last week from a Danish study of more than 650,000 children with more than 5 million person-years of follow-up. Autism risk was not increased in the vaccinated children. There were no study subgroups, such as children with autism risk factors, in which the vaccine was associated with an increased autism risk. I cannot be more clear: The risks of vaccines are nowhere near the risks of the diseases they prevent. Measles is no exception.

Ironically, although we are confident the vaccine is safe, a measles infection in pregnancy may lead to autism in the child. We just published a manuscript in JAMA Psychiatry describing an increased risk of autism and depression in children exposed to a severe infection in pregnancy in Swedish women  who were hospitalized between 1973 and 2014. This time span included nearly 2 million pregnancies with up to 41 years of follow-up, which provided striking evidence that a severe infection, like measles, can result in inflammation that can disturb fetal brain development and increase risk for mental-health disorders.

Even if you’ve had the measles, mumps and rubella vaccine, up to 3 percent of individuals may not be completely protected. In pregnant women who received the vaccine 35-40 years ago, their immunity from the vaccine may not be enough to provide protection. Unfortunately, we can’t give the measles vaccine during pregnancy, which leaves women with uncertainty as to whether they are immune.

For pregnant women living near an active measles outbreak or planning travel there, talk to your doctor or medical provider about measles. In my opinion, the only safe approach for pregnant women and infants is to avoid traveling to Clark County and the many other places in the world where measles is currently spreading. This includes places like the Ukraine, Philippines, Brazil and Madagascar, where hundreds of people have died of measles and tens of thousands have been infected in the last year.

To people who willingly choose not to vaccinate, it is my duty to remind you of the risk you introduce into your homes, schools and communities. I urge you to re-examine the information that has led to this choice. Please trust in the decades of research proving the safety and effectiveness of the measles vaccine. Please also remember that, if you choose not to vaccinate your child, you have made a choice to put pregnant women and their newborns in your immediate community at risk. A measles infection could cost our patients their pregnancy or even their life.