Despite recommendations to get the flu shot, most pregnant women do not. In the U.S., only between 10 percent and one-quarter of women have been vaccinated each flu season over the last couple decades, Sheffield's team notes.
Based on studies, that seems largely due to safety worries.
On the other hand, Sheffield said "it's amazing" how many women are unaware that the flu itself is considered a risk during pregnancy.
"The flu is a problem in pregnancy," she said. "But we have a vaccine to prevent it. And it's considered safe and effective in any trimester."
Image: Woman gets flu shot via Shutterstock.