High blood levels of the vitamin folate appear to increase the risk of a twin birth after women are impregnated through in vitro fertilization (IVF) or other assisted reproduction techniques, British doctors have found.

Folate, a B vitamin found in green leafy vegetables, cereals and liver, is essential for fetal growth. Women are advised to take folic acid supplements, a synthetic compound of folate, before becoming pregnant and during the early months of pregnancy, to curb the risk of defects such as spina bifida, a defect of the spine.

A goal of doctors who perform IVF is to increase the rate of successful pregnancies, so they usually implant more than one embryo. However, this practice leads to an increased risk of multiple births, which in turn raises the risk of death and illness for both the mothers and the infants.

Dr. Paul Haggarty, from Aberdeen University, and his associates prospectively evaluated outcomes for 602 women undergoing fertility treatment. Their findings appear in The Lancet this week.

In the IVF group, 32 percent of attempts resulted in a fetus with a heartbeat, and 29 percent in live births. There were 93 singleton pregnancies and 37 twin pregnancies.

Younger women were more likely to have twins, the team found. The rate of twins was also associated with higher levels of folate.

However, folate concentrations were unrelated to the likelihood of successful pregnancies, according to the report.

Haggarty’s team advise doctors to recommend to women undergoing assisted reproduction that they not exceed recommended doses of folic acid.

They also note that if folic acid fortification of the UK diet becomes mandatory in order to reduce the rate of neural tube defects, the number of multiple gestations associated with infertility treatment will increase.

SOURCE: The Lancet, May 6, 2006.