Maternal and fetal plasma homocysteine concentrations at birth: the influence of folate, vitamin B12, and the 5,10-methylenetetrahydrofolate reductase 677C-->T variant.

OBJECTIVE: The purpose of this study was to determine the nutritional and genetic factors that influence fetal plasma homocysteine concentrations.

STUDY DESIGN: Maternal and umbilical cord venous blood was taken from 201 women who were delivered after uncomplicated pregnancies of 37 to 41 gestational weeks. Red blood cell folate, plasma folate, plasma vitamin B12, and plasma homocysteine concentrations were measured in all samples. Cord and maternal bloods were also genotyped for the 677C-->T variant.

RESULTS: The fetal circulation had lower homocysteine concentrations (7.87 +/- 2.87 micromol/L; mean +/- SD) than the maternal circulation (8.34 +/- 2.94 micromol/L; P =.003), but there was a strong linear association between the levels in these 2 compartments (r = 0.72; P <.0001). Overall, the maternal homocysteine level had the strongest influence on the fetal homocysteine concentration (P <.0001), with the fetal and maternal vitamin B12 having important additional effects (P =.016 and P =.0045, respectively). Fetal plasma folate and 5,10-methylenetetrahydrofolate reductase 677C-->T genotype had no significant effects (P =.23 and P =.54, respectively), probably because of folic acid supplement use.

CONCLUSION: The maternal homocysteine level is the primary predictor of blood homocysteine in the developing fetus. If lowering maternal blood homocysteine proves critical to preventing pregnancy complications, it will be important to maintain optimal vitamin B12 status in addition to optimal tissue folate status.