Trends and Prevalence of Modifiable Risk Factors for Birth Defects Among U.S. Women of Reproductive Age: National Health and Nutrition Examination Survey 2007 to March 2020.

Introduction: Congenital heart defects, orofacial clefts, and neural tube defects share similar modifiable risk factors. The prevalence and trends of risk factors for these selected birth defects were assessed among nonpregnant, nonlactating women of reproductive age (aged 12-49 years) in the U.S.

Methods: Cross-sectional data from the National Health and Nutrition Examination Survey 2007-March 2020 were analyzed in fall 2024. Demographics, BMI, household food security, folic acid supplement use, usual intake of dietary folate and vitamin B12, concentrations for serum and red blood cell folate, serum vitamin B12, serum cotinine (smoking exposure), and diabetes status were reported. Weighted percentages of prevalence of risk factors with 95% CIs were calculated using the survey package in R to account for clustered sampling.

Results: Among 5,374 women of reproductive age, approximately 66.4% (95% CI=64.3, 68.4) had at least 1 known modifiable risk factor: 6.7% (95% CI=5.7, 7.6) reported very low food security, 33.8% (95% CI=32.2, 35.4) had obesity, 4.8% (95% CI=4.0, 5.5) had diabetes, 18.8% (95% CI=17.2, 20.4) had smoking exposure, and 19.5% (95% CI=17.8, 21.1) had red blood cell folate concentrations below the threshold (748 nmol/L) for optimal neural tube defect prevention. Over the time studied, the percentage of women of reproductive age with at least 1 risk factor rose from 65.3% (95% CI=62.1, 68.4) to 69.5% (95% CI=65.4, 73.9; p=0.08).

Conclusions: Approximately 2 of 3 women of reproductive age in the U.S. have pre-existing modifiable risk factors for birth defects. Implementation of preconception health care could help reduce the prevalence of known risk factors and improve birth outcomes.