RESUMEN
BACKGROUND: In 2000, Chile's Ministry of Health mandated fortification of wheat flour with folic acid at a concentration of 2.2 mg/kg to prevent neural tube defects (NTDs), resulting in a 50% reduction in NTD prevalence. Concerns about possible collateral effects of high folic acid intake led, in 2009, to decrease the folic acid fortification to 1.8 mg/kg of flour. Our study evaluated the impact of this modification on the prevalence of NTDs in Santiago. METHODS: This study measured the prevalence of NTDs in live births and stillbirths born in Santiago. We calculated prevalence ratios (PR) and 95% confidence intervals (CI) between pre-folic acid fortification (1999-2000), post-folic acid fortification (2001-2009), and post-modified folic acid fortification (2010-2015) periods for all NTDs and their specific types. We used chi-square tests to analyze proportions, and a Joinpoint regression to visualize prevalence time trends. RESULTS: The NTD prevalence for the period 2001-2015 was 8.9 per 10,000 births, which represents a 48% reduction (PR = 0.52; 95% CI = 0.45-0.61; p < .001) from the pre-folic acid fortification period. During 2010-2015, the NTD prevalence was 9.5/10,000 births, which was higher, but not statistically significantly different from 2001 to 2009 prevalence of 8.6/10,000 (PR = 1.11; 95% CI = 0.96-1.30, p = .17). CONCLUSIONS: Decreasing the concentration of folic acid fortification was not associated with a statistically significant change in the prevalence of NTDs. Mandatory folic acid fortification continues to be a safe and highly effective policy to prevent NTDs. Future studies should evaluate the prevalence of NTDs across Chile and adherence to folic acid fortification mandates.