1. We measured erythrocyte folic acid and riboflavin, serum folic acid and leucocyte vitamin C in women at high risk for neural tube defect (NTD) recurrence who were receiving periconceptional vitamin supplementation, before they received extra vitamins, after 28 d of supplementation and at the 8th week of pregnancy. Blood vitamin concentrations in unsupplemented high-risk women were also compared with the values found in unsupplemented low-risk women.
2. Vitamin supplementation with Pregnavite Forte F (Bencard®) raised the mean values for all vitamins measured by the 8th week of pregnancy. Mean erythrocyte folic acid rose from 250 to 478 ng/ml; plasma folic acid from 8·4 to 26·1 ng/ml; leucocyte vitamin C from 1·82 to 3·21 μg/ml blood; erythrocyte riboflavin (glutathione reductase (EC 220.127.116.11) activation ratio) from 1·08 to 1·04. All women receiving supplements had increased their serum and erythrocyte folic acid levels above the highest values found in women in an earlier study, who subsequently gave birth to children with NTD. Not all women, however, increased their leucocyte ascorbic acid or erythrocyte ribflavin levels above the highest values.
3. When vitamin concentrations in unsupplemented high-risk women were compared with levels in unsupplemented women at low risk for NTD, no significant differences were found in the mean values. However, a significantly higher proportion of high-risk compared with low-risk women had erythrocyte folic acid and leucocyte vitamin C values on or below the 5th percentile of the adult normal range.
4. The effectiveness of Pregnavite Forte F (Bencard®) for increasing maternal vitamin reserves is discussed with a view to preventing NTD and the possibility of identifying groups at risk for NTD because of low blood vitamin levels is considered.