As we all know, a woman’s body changes enormously during pregnancy — a growing belly, swollen feet. It turns out that one of the most significant changes women experience is invisible to the naked eye: Pregnancy applies the brakes to the mother’s immune system.

“A pregnant woman’s immune system changes in important ways to allow a fetus to develop within her own body without rejecting it,” says Kristina Adams Waldorf, MD, Res. ’02, professor of obstetrics and gynecology and adjunct professor of global health.

At the same time, however, a weaker immune defense in the placenta presents an opportunity for harmful viruses and bacteria to infect the mother and child. And these infections have consequences.

Recently, Adams Waldorf and a research team at the University of Gothenburg in Sweden, where she holds a joint appointment, released the findings from a study. Using the Swedish National Birth and Health Registries, the investigators followed the outcomes of more than 4 million pregnancies and the health of the children for over 40 years. Published in JAMA Psychiatry, the researchers’ findings revealed that if a pregnant woman had been hospitalized with an infection — from the flu, for example — her child was more at risk for developing autism and depression.

Although previous research had shown that infections can injure the fetal brain, this was the largest and most definitive study to demonstrate a long-term impact on the mental health of the child across a broad spectrum of infections. The study highlights the important role vaccines play in protecting not only the mother’s health, but also the health of her fetus and future child.

“Wouldn’t it be incredible if we could use vaccination to protect not only pregnant women, but also the fetal brain when it is at its most fragile stage of development?” asks Adams Waldorf.

Adams Waldorf is also researching medications that could be helpful in protecting the fetus from dangerous infections like the Zika virus, which has been linked to devastating fetal brain injuries. Thanks to the work of Adams Waldorf and her colleague Michael Gale, Jr., PhD, the director of UW Medicine’s Center for Innate Immunity and Immune Disease, researchers are now certain that the Zika virus is dangerous during pregnancy. However, they still don’t know exactly how the Zika virus tricks the early immune response, allowing it to spread and cause damage.

Understanding the intricate, nuanced ways that the immune system interacts and responds to infections like Zika is key to protecting pregnant women and their fetuses from the next viral outbreak or epidemic.

“If we can harness the full power of the maternal and fetal immune system, we can prevent millions of deaths in children around the world,” says Adams Waldorf.

Illustration: Kary Lee