Most Women Have Modifiable Risk Factors for Birth Defects (2025)

The proportion of women with modifiable risk factors for serious birth defects is growing, suggested an analysis of more than a decade's worth of National Health and Nutrition Examination Survey (NHANES) data.

Among more than 5,000 reproductive age women, 66.4% had one or more known modifiable risk factors, with this percentage rising from 65.3% in 2007-2010 to 69.5% in 2015-2020, according to Arick Wang, PhD, of the CDC's National Center on Birth Defects and Developmental Disabilities in Atlanta, and colleagues.

Three or more known risk factors were found in 10.4% of the women, they reported in the American Journal of Preventive Medicine.

In terms of the modifiable risk factors, 33.8% of participants had obesity, 19.5% had red blood cell (RBC) folate concentrations below optimal thresholds for preventing neural tube defects, 18.8% had smoking exposure, 6.7% reported very low food security, and 4.8% had diabetes. Rates of diabetes and prediabetes nearly doubled across the study period.

The results highlight "how common these changeable risk factors are," Wang said in a press release. "The good news is that they can be lowered."

"Birth defects form early in pregnancy, often before a woman knows she is pregnant," Wang told MedPage Today. "Beginning conversations before pregnancy can help prevent birth defects and support healthier outcomes for both moms and babies."

Food insecurity, folate insufficiency, vitamin B12 deficiency, pregestational diabetes or obesity, and exposure to cigarette smoke are all known modifiable risk factors for birth defects, and some of these are also associated with other adverse pregnancy outcomes, the researchers noted. Congenital heart defects, orofacial clefts, and neural tube defects are among the most common birth defects in the U.S., affecting about 100 per 10,000 live births, 16 per 10,000 live births, and 7 per 10,000 live births, respectively.

Daily folic acid supplementation (400 µg) has been recommended to women for preventing neural tube defects for decades, and the FDA mandated the enrichment of grains with folic acid in 1996 and voluntary fortification of corn masa products in 2016.

"Every growing family hopes for a healthy pregnancy and healthy baby," said Wang. "Understanding modifiable risk factors for birth defects helps families, healthcare providers, and public health professionals make data-informed decisions that can lead to healthier pregnancies and babies."

Among the women in the current study, 28% supplemented with folic acid, but only 12.6% supplemented with the recommended amount. Overall consumption of folic acid-containing supplements did not trend downward across the study period, however the use of supplements meeting the recommended dose did.

Still, most of the women reached the recommended RBC folate concentrations of >748 nmol/L for optimal neural tube defect prevention, highlighting "the importance of existing public health programs such as food fortification in [neural tube defect] prevention," the authors wrote.

David Hackney, MD, a maternal-fetal medicine physician at Case Western Reserve University in Cleveland, told MedPage Today that pregnancy and its subsequent outcomes do not simply occur "in a silo -- it is deeply intertwined with the degree of population health, including things like obesity and access to high-quality food."

To improve pregnancy outcomes, it's vital to improve the health of this population as a whole beforehand, said Hackney, who was not involved in the research. "Many patients don't recognize that they're pregnant until they're partway or fully through the first trimester -- or even further than that."

The study from Wang and colleagues analyzed data from the long-running NHANES surveys, which collect cross-sectional data from a nationally representative sample of U.S. households. Participants responded to two dietary intake 24-hour recall interviews and had household interviews and in-person health exams. The overall response rates ranged from 48.8% to 75.4%. Researchers analyzed NHANES data from 2007 through March 2020.

Women of reproductive age were identified by self-reported sex and age. Exclusion criteria were self-reported pregnancy or lactation or a positive pregnancy test. Only women ages 12 to 49 who completed the dietary recall and had RBC folate and fasting glucose modules were analyzed.

Among the 5,374 participants, 34.2% were ages 12 to 24 years, 25.1% were ages 25 to 34, and 40.6% were ages 35 to 49 years. Most participants were non-Hispanic white (57.8%) while 13.9% were non-Hispanic Black, and 19% were Hispanic.

As for limitations, the authors noted that some strata in the NHANES had limited sample size, that serum vitamin B12 concentrations were only captured from 2011 to 2014, that some data may not reflect clinical definitions, and that their analysis didn't account for all possible risk factors.