RESUMEN
Guidelines recommend that women take folic acid supplements in the preconception period to prevent neural tube defects (NTDs) in their offspring. Estimates of adherence to this recommendation across different countries worldwide have not been synthesized. Medline, CINAHL, and EMBASE were systematically searched to identify studies reporting the prevalence of preconception folic acid supplementation. Pooled prevalence estimates for each country (where data were available) were calculated; and differences based on demographic, methodological, and study quality characteristics were examined. Of 3372 titles and abstracts screened, 722 full-texts were reviewed and 105 articles that reported 106 estimates of preconception folic acid supplementation in 34 countries were included. Pooled prevalence estimates were 32-51% in North America, 9-78% in Europe, 21-46% in Asia, 4-34% in the Middle East, 32-39% in Australia/New Zealand, and 0% in Africa. No South American studies were identified. Higher supplementation prevalence was observed in studies that had more highly educated samples, were conducted in fertility clinics, and assessed folic acid use via self-report. Of note, only 32% and 28% of studies reported timing of folic acid use and adherence to folic acid, respectively. Preconception folic acid supplementation is highly variable worldwide and many women may not achieve sufficient folate levels to prevent NTDs. To better understand non-adherence, recommendations for future research include: more explicit reporting of methodology, more detailed assessment of folic acid use, assessment of variables potentially relevant to folic acid use, and surveillance of folic acid use in a greater diversity of countries, especially in the developing world.