High folate hikes odds of twinning after IVF.(Obstetrics)

A high plasma folate level around the time of conception raises the chance of twinning after in vitro fertilization, but not the chance of having a successful pregnancy, reported Paul Haggarty, Ph.D., of the Rowett Research Institute, Aberdeen, Scotland, and his associates.

"Our results suggest that the high incidence of twin births associated with treatment for infertility could be reduced, while maintaining [live birth] rates, by encouraging women not to exceed recommended doses of folic acid and by identifying those at high risk of twins after double-embryo transfer on the basis of their plasma folate concentrations and age," they wrote (Lancet 2006;367:1513-9).

"The need to increase the intake of folic acid to reduce the incidence of neural tube defects is not in doubt, but the associated risks of multiple births after IVF need to be addressed," they noted.

High folate levels have been associated with an increase in natural twinning, and "there are good biological reasons to suspect that B-vitamin exposure" also affects twinning in IVF pregnancies. Dr. Haggarty and his associates assessed vitamin B intake, plasma and red cell levels of folate, and six variants in genes known to be involved with B-vitamin metabolism in 602 women undergoing IVF. For comparison, they also performed the same genetic analysis in 932 women who had conceived naturally and had singleton pregnancies.

Folate and vitamin B intake correlated with plasma and red-cell levels of folate. Neither one was associated with the rate of live births or the rate of pregnancy loss after IVF. However, both were associated with an increased rate of twinning in the IVF group.

Younger maternal age also was associated with an increased rate of twinning.

Women in the United Kingdom who are trying to conceive either naturally or through IVF are advised to take 400 mcg of supplementary folic acid daily before and after conception, to reduce the ...