The impact of voluntary folate fortification of corn masa flour on US pregnancies complicated by neural tube defects

INTRODUCTION: In 1996, the US Food and Drug Administration (FDA) mandated folic acid fortification for all enriched cereal grains. This resulted in a reduction of neural tube defect (NTD)–affected pregnancies. However, Hispanic women continued to be twice as likely to give birth to a child affected by NTD compared to non-Hispanic White women. Some hypotheses explaining this difference focus on cultural variation in dietary intake of cereal grains. In 2016, the FDA approved voluntary folic acid fortification for corn masa flour products to focus on the Hispanic diet staple. This study investigates rates of NTDs in predominantly Hispanic-populated zip codes before and after the voluntary fortification of corn masa flour with folic acid. METHODS: Normal pregnancies and those complicated by NTDs between 1/1/2016 and 9/30/2020 were identified using ICD-9 and ICD-10 codes in an all-payor claims database. The post-fortification period began 12 months after the fortification recommendation. The US Census data was used to stratify pregnancies in predominantly Hispanic zip codes (≥ 75% of households) vs. non-Hispanic zip codes. The causal impact of the FDA’s recommendation was assessed by means of a Bayesian structural time series model. RESULTS: A total of 2,584,366 pregnancies were identified among females aged 15–50 years. Of these, 365,983 took place in predominantly Hispanic zip codes. Mean quarterly NTDs per 100,000 pregnancies did not significantly differ between predominantly Hispanic zip codes and predominantly non-Hispanic zip codes pre-FDA recommendation (184.5 vs. 175.6; p = 0.427), nor post-recommendation (188.2 vs. 185.9; p = 0.713). Rates of NTDs predicted to occur if no FDA recommendation had been made were compared to the actual rate post-recommendation: no significant difference was observed in predominantly Hispanic zip codes (p = 0.245) or overall (p = 0.116). CONCLUSIONS: Rates of neural tube defects were not significantly reduced in predominantly Hispanic zip codes following the 2016 FDA approval of voluntary folic acid fortification of corn masa flour. Further research and implementation of comprehensive approaches to advocacy, policy, and public health are necessary to decrease preventable congenital disease rates. Mandatory rather than voluntary fortification of corn masa flour products may achieve more substantial prevention of neural tube defects in at-risk US populations. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00381-023-05945-w.