The research involved women who were having treatment to boost their fertility but as there were no side effects from taking the vitamins, scientists said all women who are trying to conceive should consider them.

In the study half of women were given a multivitamin and mineral tablet to take each day and half were given folic acid, recommended by government to prevent abnormalities in the baby.

Four weeks later they then had a fertility drug treatment.

Women on the vitamins were more likely to conceive and 60 per cent were still pregnant three months later compared to 25 per cent on folic acid.

They were also likely to fall pregnant after fewer fertility treatments with three quarters conceiving on their first cycle, compared with less than one in five of those on folic acid, it was found.

The study conducted by researchers at Warwick University involving 56 women attending University College London and the Royal Free Hospital fertility units.

The women, who were mostly from an affluent background, all had healthy diets at the beginning of the study and later blood tests showed those on the multivitamin had higher levels of micronutrients than those only taking folic acid.

The multivitamin used was Pregnacare Conception made by Vitabionics but the company did not commission, fund or influence the study. They provided the vitamins used which usually cost £10.15 for a pack of 30.

Lead author Dr Rina Agrawal, consultant obstetrician and gynaecologist and Associate Professor in Reproductive Medicine, said: "All women considering pregnancy should take a specifically formulated prenatal micronutrient supplement to optimise their chances of conception."

She said it is not known what components of the vitamin tablet had the effects on pregnancy but the Pregnacare Conception product used contained a range of vitamins, minerals, antioxidants and substances linked to ovarian function and blood flow to the reproductive organs.

The findings are being published in the Reproductive BioMedicine Online journal.

Prof Alison Murdoch, Professor of Reproductive Medicine at Newcastle University said: “This is not a well designed study; the numbers are small and they have not provided any evidence of causation.

"The results are unusual and difficult to explain. They describe it only as a pilot study – which it clearly is.

"I know it will cause unnecessary anxiety for infertile patients. A good diet is important if you are trying to conceive but most of us get sufficient nutrition in a normal diet and unless there is no evidence of dietary deficiency, this does not provide evidence of the need for supplements.”

Dr Allan Pacey, Senior Lecturer in Andrology at the University of Sheffield said “The influence of nutrition on our fertility is of general interest to the public and professionals, but there are relatively few studies which have examined this systematically and few which have shown direct benefits of taking supplements to enhance things."

“Therefore, on the face of it, this study is interesting but we should acknowledge that this is a relatively small number of patients and the study would need to be repeated in a larger trial before we could be certain of the results.

“I can't help but thinking that for most people, just general dietary advice would achieve the same effect and a good basket of fresh fruit and vegetables from the greengrocer each week would have much the same effect if their diet was poor.”

Glenys Jones, a Nutritionist at the Medical Research Council's Human Nutrition Research said: “This is an interesting study and supports the body of evidence that diet plays an important role in supporting women's health and their fertility.

"However this study alone cannot result in the general recommendation that all women undergoing fertility treatment should take a preconception multivitamin as it is a very small single study and further large-scale research is required to investigate if this is reproducible in a larger more diverse group of women.”

Catherine Collins, Principal Dietician, St Georges Hospital NHS Trust said: “Although the researchers claimed their diets were nutritionally adequate no robust data was provided to confirm this – a major concern for any trial making nutritional claims.

"We know that broad-spectrum supplements can correct dietary deficiencies and boost blood levels of iron, B12, folic acid and vitamin D - as was shown in this study which suggests these women had low intakes pre-conception.

“As this study was of women with conception problems there’s no evidence to suggest every woman considering pregnancy should take them.

"Similarly, n-acetyl cysteine and arginine have been shown to improve the efficacy of IVF treatments in a small number of studies, but there’s no evidence to support their use in natural conception. However, the nutritional advice for women contemplating pregnancy remains unchanged – take folic acid supplements until 12 weeks of pregnancy and if you decide on a multi-nutrient supplement for nutritional insurance make sure it’s one suitable for pregnancy, as the vitamin A content is lowered to ensure safety of the developing baby.

"But it’s important to remember a supplement can’t substitute for a varied healthy diet providing sufficient protein and calories to sustain a healthy pregnancy.”

A larger study is underway.