Spina bifida before and after folic acid fortification in Canada.

BACKGROUND: In 1998, fortification of a large variety of cereal products with folic acid became mandatory in Canada. A multicentric study was carried out to assess the impact of this policy on the frequency of NTDs. The present analysis focused on spina bifida.

METHODS: The study population included approximately 2 million livebirths, stillbirths, and terminations of pregnancies because of fetal anomalies among women residing in seven Canadian provinces, from 1993 to 2002. Spina bifida cases were divided according to the upper limit of the defect: upper (cranial, cervical, or thoracic) and lower (lumbar or sacral) defects. Based on published results of red blood cell folate tests, the study period was divided into prefortification, partial fortification, and full fortification periods.

RESULTS: A total of 1,286 spina bifida cases were identified: 51% livebirths, 3% stillbirths, and 46% terminations. Prevalence decreased from 0.86/1,000 in the prefortification to 0.40 in the full fortification period, while the proportion of upper defects decreased from 32% to 13%. Following fortification, regional variations in the prevalence and distribution of sites almost disappeared.

CONCLUSIONS: Results confirmed the etiologic heterogeneity of spina bifida and the more pronounced effect of folic acid in decreasing the risk of the more severe clinical presentations.