Multivitamin supplements that are promoted to pregnant women are not needed by most mothers-to-be and are simply an unnecessary expense, it has been claimed.

A review of all the available evidence on multivitamin and mineral supplements was carried out and it concluded that pregnant women should resist the marketing claims made by these products.

It noted that good nourishment before and during pregnancy is key for women and their unborn children and deficiencies in key nutrients have been linked with a number of pregnancy and birth complications, such as pre-eclampsia, low birth weight and neural tube defects.

Many multivitamin and mineral supplements are marketed towards pregnant women, which claim to reduce the risk of certain health issues. These usually contain at least 20 vitamins and minerals such as vitamins C and D, iodine, iron and selenium.

The review was carried out by the journal, Drug and Therapeutics Bulletin (DTB), a monthly journal from the UK which carries out rigorous evaluations of treatments and the overall management of diseases.

The review found that claims in relation to folic acid are accurate. Folic acid is known to reduce rates of neural tube defects, which are birth defects of the brain, spine or spinal cord. Spina bifida is the most common NTD.

Taking folic acid before conception and during the early stages of pregnancy has been proven to prevent up to 70% of these defects and this supplement should continue to be taken.

However, when it came to other vitamins and minerals, the evidence was less clear. For example, vitamin D supplementation did not appear to reduce the risk of pregnancy and birth complications, while other supplements did not appear to offer any clinical benefit to well-nourished women.

DTB noted that a lot of the evidence in relation to these products comes from low-income countries where women are more likely to be malnourished or undernourished.

Furthermore, a lot of these studies were observational, which can only establish a link, not a cause.

"For most women who are planning to become pregnant or who are pregnant, complex multivitamin and mineral preparations promoted for use during pregnancy are unlikely to be needed and are an unnecessary expense. The marketing of such products does not appear to be supported by evidence of improvement in child or maternal outcomes," DTB said.

It added that pregnant women ‘may be vulnerable to messages about giving their baby the best start in life, regardless of cost'.