Taking folic acid supplements prior to pregnancy does not increase the likelihood of giving birth to twins, scientists have found.

Folic acid supplements are taken by women wishing to conceive to reduce the risk that their baby will develop neural-tube defects - a malformation of the spinal cord that can cause severe handicap.

Among women who have already had at least one child with neural-tube defects, taking folic acid (0.4 mg daily) for at least one month before conception can reduce the risk by 72%. The risk of complications is also substantially reduced among women who have not previously had such complications.

Hungarian researchers found that the rate of multiple births in women taking multivitamins - including a low dose of folic acid - was increased.

But no such link has been found by two UK studies which looked at the folic acid intake of more than 2,000 women:

• The MRC Vitamin Study, a trial which examined the effect of folic acid on the incidence of neural-tube defects;
• The Prospective Study of Nutrition, Smoking and Pregnancy Outcome, which investigated the use of folic acid before and during pregnancy in English women.

The researchers, writing in The Lancet medical journal, conclude that there is no evidence that folic-acid supplementation is associated with an increased rate of twinning.

One of the study authors, Dr Fiona Mathews, from Oxford University, said women may have been dissuaded from taking folic acid if they thought there was a chance of a multiple birth.

"There could also have been very important public health considerations," she said.

"Twins carry substantially more risk than a normal pregnancy. There is a higher risk of pre-term birth and of miscarriage."

Publicity drive

Folic Acid safeguards against birth defects

Research in the Dutch city of Nijmegen has found that a joint sustained effort by health authorities, the media and health care professionals can significantly boost the number of women who take folic acid supplements.

Prior to a publicity campaign in 1992, less than 10% of women who wanted to conceive took folic acid, but the proportion rose to about 70% following a concerted media campaign.

In the UK, approximately one in three women who want to get pregnant currently take folic acid supplements.

Doctors recommend that women take 4mg a day in supplements, assuming that they take in an additional 2mg a day from their natural diet.

Dr Mathews said the UK research found that only one woman in 1,000 took in sufficient folic acid from her diet alone.

"The idea that simply eating enough brocolli is going to give you enough folic acid is not really borne out. You would need a bizarre diet to achieve that," she said.