Neural tube defects

The primary finding reported by Joel Ray and associates1 in their study of ethnicity in relation to the development of neural tube defects — that babies born to First Nations women have a higher risk of neural tube defects — should be interpreted with caution.

The calculation of the relative risk of a neural tube defect for a child with a First Nations mother is based on 5 cases occurring among 1551 subjects. The ethnicity category for “other” (which included Hispanic women) had 1 case among 10 009 subjects. The protective effect observed in this group was not mentioned in the study's interpretation, despite the broader base of subjects.

Such small numbers may cause several problems. One is that a few misclassifications of the First Nations cases could create the appearance of an effect where none actually exists. Also, given that multiple categories were examined, the authors should have considered some form of adjustment for multiple comparisons.2

In general, one should be careful not to overinterpret results obtained in small subpopulations. While the hypothesis suggested by Ray and associates is intriguing, we should gather more evidence before changing policy.