Changes in Frequencies of Select Congenital Anomalies since the Onset of Folic Acid Fortification in a Canadian Birth Defect Registry

Article excerpt

ABSTRACT

Objectives: Fortification of grain products with folic acid has been shown to significantly reduce the occurrence of neural tube defects (NTDs) in Canada and elsewhere. However, the impact on non-NTD anomalies has not been well studied.

Methods: Using the Alberta Congenital Anomalies Surveillance System (ACASS), we examined changes in occurrence of select congenital anomalies where folic acid supplementation with multivitamins had previously been suggested to have an effect. Anomalies documented in the ACASS 1992-1996 (pre-fortification) were compared to 1999-2003 (post-fortification).

Results: A significant decrease in spina bifida (OR 0.51, 95% CI 0.36-0.73) and ostium secundum atrial septal defects (OR 0.80, 95% CI 0.69-0.93) was evident, but there was a significant increase in obstructive defects of the renal pelvis and ureter (OR 1.45, 95% CI 1.24-1.70), abdominal wall defects (OR 1.40, 95% CI 1.04-1.88) and pyloric stenosis (OR 1.49, 95% CI 1.18-1.89).

Conclusions: Consistent with other studies, a 50% reduction in spina bifida was associated with the post-fortification time period. Supporting the possibility that folic acid fortification may play a role in preventing other birth defects, a 20% reduction in atrial septal defects was also associated. The increase in abdominal wall defects, most notably gastroschisis, is likely related to pre-existing increasing trends documented in several regions around the world. The increase in pyloric stenosis and obstructive urinary tract defects was not expected and any causal relationship with folic acid fortification remains unclear. Similar studies by other birth defects surveillance systems in Canada and elsewhere are needed to confirm these trends.

Key words: Folic acid; heart septal defects, atrial; congenital abnormalities; pyloric stenosis; gastroschisis

Congenital anomalies are a major cause of morbidity, disability and mortality among children, contributing significantly to health care costs.1-3 The discovery of folic acid as a simple and economical way to prevent at least neural tube defects (NTDs) was therefore an important public health success. Indeed, here in Canada, a recent multicentre study has confirmed an associated 46% reduction of NTDs since the onset of folic acid fortification of grain, supporting the effectiveness of the public health initiative. 4 There is now interest in whether folic acid will reduce rates of other birth defects.5-7

It has been long established that periconceptional use of vitamin supplements containing folic acid reduces the risk of neural tube defects (NTDs).8,9 This information led to recommendations of periconceptional folic acid supplementation of 0.4 mg/day for all women of childbearing age and an increased amount (0.8-5 mg daily) for higher risk women (those with diabetes, taking anti-epileptic drugs, or previous NTD-affected pregnancies).10,11 Fortification of grain products with folic acid was implemented to ensure that the majority of women have the benefit of at least some folic acid intake during the periconceptional time frame.12 In December 1996, Canada, along with the US, allowed the addition of folic acid to white flour, enriched pasta and cornmeal.12 Mandated in Canada by November 1998, the level of fortification was estimated to increase the average daily intake of folic acid in women of childbearing age by about 0.1 mg.13

Evaluation of the fortification program has been largely focused on significant reductions in NTDs and has been declared successful in the US and Canada.4,14-17 The significant decline temporally associated with fortification provides convincing evidence that folic acid is the nutrient responsible.

For non-neural tube birth defects, there is evidence that periconceptional use of multivitamin supplements containing folic acid and other vitamins is associated with decreased occurrence of some anomalies including: orofacial clefts,6,18-23 limb reduction defects,6,20,24,25 urinary tract defects,6,20,26,27omphalocele,28 conotruncal and septal heart defects,6,24,29,30 and pyloric stenosis. …