A new study estimates that 54% of pregnancies that result in a live birth in the United States involve some exposure to alcohol, HealthDay reports.

Researchers at Yale University used a computer simulation model of U.S. women of reproductive age. They calculated that 12% of developing fetuses are exposed to five or more drinks in a week at least once during the pregnancy, and 3% are exposed to nine or more drinks in a week. They estimated that 80% of pregnancies that were unknowingly exposed to alcohol were unintended.

“When we consider alcohol-exposed pregnancies, much of the focus is on women who are aware of their pregnancies but may continue to drink,” lead researcher Reza Yaesoubi said in a news release. “But what we found in this study is that among pregnancies that are exposed to alcohol, in fact, more than half are exposed while the pregnancy is still unrecognized.”

Alcohol use during pregnancy is associated with a range of adverse outcomes. It can cause fetal alcohol spectrum disorders that are characterized by lifelong physical, behavioral and intellectual disabilities, the researchers noted.