A gene defect may be responsible for some miscarriages, according to experts.

The flaw, which is carried by millions of women worldwide, could increase the risk of unsuccessful pregnancy - and even the chances of the infant dying after birth.

However, the research has only been carried out on mice so far, and UK experts have warned that it needs to be backed up by human-based studies.

Mice with the defect had smaller litters

The genetic defect leads to a deficiency of a common enzyme, or chemical, produced by the body.

This usually neutralises potentially harmful molecules called "free radicals" which can cause cell damage.

If human studies reinforce the findings of this research, it may be possible to give women at risk doses of antioxidants - which can also help deal with free radicals.

Miscarriage happens in approximately 15% of all pregnancies, and are normally unexplained.

Tiny litters

The latest research, by scientists at the University of Toronto, published in Wednesday's New Scientist magazine, found that mice producing low levels of the enzyme, called G6PD were at higher risk of problems during and even after pregnancy.

The mice with the genetic defect had litters only half as large as normal when mated with males carrying the same defective gene.

Instead of miscarrying, mice tend to reabsorb their embryos.

They also saw three times as many pups die during the period between birth and weaning.

It's a matter of urgency now to take these studies forward in humans

Professor Lesley Regan

It appeared to be the genes passed on to the mouse foetus that made all the difference - if a mouse could produce enough G6PD, it tended to survive, even when carried by an enzyme deficient mother.

Professor Lesley Regan, and expert in miscarriage based at St Mary's Hospital in London, said: "It's a matter of urgency now to take these studies forward in humans."

She warned women not to take too many antioxidants - as this could have unknown side-effects.

She said: "The vast majority of miscarriages are actually due to major genetic abnormalities in the baby which are incompatible with life."

She said that gene research could yield treatments for women prone to miscarriage in just a few years.

It is thought that up to 400 million, or nearly seven per cent of the world's population have the deficiency.

In some populations, such as Africa, Asia and the Mediterranean, the rate is as high as 65%.

Additional risk is faced by women who have the genetic defect, and who take the anticonvulsive drug phenytoin for conditions such as epilepsy.