Ireland has a high rate of neural tube defects, and NIH scientists have frequently collaborated with Irish researchers to gain insight into the causes of this group of disorders.
To conduct the study, the researchers analyzed stored blood samples originally collected during early pregnancy from three groups of Irish women between 1983 and 1990. During that time, pregnant women in Ireland rarely took vitamin supplements. The study authors reasoned that the lack of routine vitamin supplementation would allow them to identify a sufficient number of women with low Vitamin B12 to conduct their analysis.
For their analysis, the researchers classified the women into three groups. The first group consisted of 95 women who were pregnant with a child having a neural tube defect at the time the blood was taken. The second group was composed of 107 women who had previously given birth to a child with a neural tube defect but whose current pregnancy was not affected. Like the first group, women in the third group (a total of 76) were pregnant with a child having a neural tube defect at the time the blood sample was obtained, but were enrolled in a different study than the women in group 1. The researchers measured the Vitamin B12 and folate levels of the women's blood samples, and compared them to those of control groups whose pregnancies were unaffected by a neural tube defect.
Because low folate levels are a known risk factor for neural tube defects, the researchers used statistical techniques to evaluate the role of Vitamin B12 independently of the role of folate. In all three groups, women with low B12 concentrations (estimated at less than 250 ng/L, before pregnancy) had 2.5-3 times the risk of having a child with a neural tube defect compared to those with higher levels. Women with levels in the deficient range (0-149 ng/L ) were a
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NIH/National Institute of Child Health and Human Development