Occurrence of low birthweight and preterm delivery among California infants before and after compulsory food fortification with folic acid.

Objectives: Studies suggest that folic acid intake influences the occurrence of low birthweight and preterm delivery. Since 1998, there has been compulsory fortification of flour and other grains with folic acid in the U.S. The objective of this study was to investigate the frequencies of low birthweight and preterm delivery after mandatory folic acid fortification among approximately six million California births.

Methods: The authors investigated prevalences of low birthweight and preterm delivery before and after compulsory fortification among 5,916,630 singleton California live births that occurred from January 1990 through December 2000.

Results: The unadjusted prevalences of very low birthweight, low birthweight, and preterm delivery did not substantially vary across birth years. That is, substantial decreased prevalences during the fortification period relative to the period preceding it were not observed. However, analyses that simultaneously adjusted for maternal age, parity, race/ethnicity, education, year of birth, and fortification period revealed the following relative risk ratios (RR) and 95% confidence intervals (CI): RR = 0.91, CI 0.88, 0.94 for very low birthweight, RR = 0.94; 95% CI 0.93, 0.96 for low birthweight, and RR = 0.96; 95% CI 0.94, 0.97 for preterm delivery.

Conclusion: Findings indicate small reductions in prevalences of these outcomes associated with the timing of fortification of the U.S. food supply.