One in 33 babies in the United States are born with birth defects. But a new study from the Centers for Disease Control and Prevention is raising awareness of ways to lower that risk.

The study points to five risk factors that public health officials — and, in some cases, women themselves — can do something about: obesity, diabetes, smoking exposure, food insecurity and low levels of folate (an essential vitamin that helps the body produce cells).

According to the study, 66% of women ages 12 to 49 have at least one of these risk factors, and 10% have three or more. The CDC’s findings, published Tuesday in the American Journal of Preventive Medicine, are based on responses from 5,374 women who completed the agency’s National Health and Nutrition Examination Survey from 2007 to 2020.

“We can’t underscore enough how important it is to raise awareness about these risk factors and encourage women to speak with their doctors if they have any concerns or questions before becoming pregnant,” Arick Wang, a health scientist at the CDC and the lead author of the new study, said via email.

She added that the “risks can be lowered through steps like getting the recommended 400 micrograms (mcg) of folic acid daily, healthy diet and exercise, and managing blood sugar.”

Birth defects are the leading cause of death in infants, according to CDC data. The risks often start before some women even know they’re pregnant. Though the causes of birth defects are largely a mystery, scientists generally recognize that some combination of genetics, environment and lifestyle factors is responsible.

“This should be a wake up call to all of us,” said Dr. Michael Warren, chief medical and health officer of March of Dimes, a nonprofit research and advocacy group focused on maternal and infant health.

“We want to make sure that people have access to nutritious foods,” said Warren, who wasn’t involved in the study. “We want to make sure that people have safe places to be physically active.”

People with food insecurity can be deficient in nutrients that are vital for a fetus’ organs to develop properly, including folate. For instance, low concentrations of folate in the blood are associated with neural tube defects — brain or spine defects that develop in the first month of pregnancy. Doctors recommend that people who are pregnant or trying to get pregnant take folic acid, the synthetic version of folate.

Since 1998, the Food and Drug ministration has required that enriched cereal-grain products be fortified with folic acid. Wang, the CDC scientist, said in a press release that the policy likely prevents more than 1,300 babies each year from being born without neural tube defects.

“The vast majority of birth defects that occur, we still don’t know why they occur,” Nembhard said. “Even when women do everything right — they don’t smoke, they don’t drink during pregnancy, they monitor caffeine intake, they exercise — you can still have an outcome that is not what you wanted.”

Warren, who until June served as associate administrator of HHS’ Maternal and Child Health Bureau, said many women might not be aware that conditions like obesity and food insecurity are also risk factors.

Obesity, which affected roughly one-third of the women surveyed, was the most common modifiable risk factor in the CDC study. Scientists aren’t exactly clear on why it’s linked to birth defects, but they suspect it has something to do with changes to a woman’s metabolism — such as the way her body manages insulin and glucose — that may lead to abnormal development in the fetus.

“When [our] cells are growing and forming organs, we really rely on everything to be working just as it should. And when you disrupt those processes, things can go awry,” Warren said.

High blood sugar from diabetes may also lead to abnormal organ development, he said. And some of the chemicals in cigarette smoke, including nicotine, can reduce the supply of oxygen to the fetus.

Warren said there’s more to be done. He pointed to Mississippi, which declared a public health emergency last week over its high infant mortality rates and pledged to eliminate “care deserts,” where women don’t have access to obstetricians.

Outside researchers lauded the study’s release amid layoffs and proposed funding cuts to the agency.

“We’re delighted that this study has been ongoing. There were some questions about whether or not it would continue,” said Wendy Nembhard, director of the Arkansas Center for Birth Defects Research and Prevention at the University of Arkansas for Medical Sciences.

The Department of Health and Human Services in March announced the termination of 2,400 CDC employees. However, a federal judge issued a preliminary ruling on Aug. 12 that blocked the layoffs for certain CDC programs, including the National Center on Birth Defects and Developmental Disabilities — the group behind the new study. At least 600 CDC employees are still expected to receive permanent termination notices.