A lack of improvement in neural tube defect prevalences in California after folate fortification

Numerous studies have demonstrated declining neural tube defect (NTD) prevalences as a result of folic acid fortification, which began in 1998. The majority of these studies evaluate the effectiveness of folic acid fortification by comparing pre-fortification and post-fortification prevalences; however, these findings may be an artifact of a declining background trend. The aim of this study was to determine whether NTD prevalences decreased more rapidly after fortification (1998-2003) than before fortification (1989-1996) after accounting for pre-existing trends. The study population included all live births and stillbirths delivered in central California counties from 1989 to 2003. Cases included pregnancies with NTDs identified by birth defects surveillance during the same time period. Using weighted least squares regression, we compared the rate of change (i.e. slope of the line) in NTD prevalences in the periods before and after fortification. For comparison, pre- and post-fortification period prevalences were also assessed. For all NTDs combined, the pre-fortification slope indicated that NTD prevalence decreased by 7.8 (slope: -7.8; 95% CI: -11.4, -4.2) cases per 100,000 deliveries per year, while the post-fortification slope increased by 5.0 (slope: 5.0; 95% CI: -2.5, 12.6) cases per 100,000 deliveries per year. A comparison of the pre- (85.23 cases per 100,000 deliveries) and post-fortification (post-fortification=72.16 cases per 100,000 deliveries) period prevalences suggested a beneficial effect from fortification. In conclusion, after accounting for the background trend, annual NTD prevalences did not decrease more rapidly after implementation of folic acid fortification; this finding contradicts previous findings that do not account for pre-existing trends.