Pregnant women are a soft target for such products. (Representational Image)
Multivitamins and mineral supplements in pregnancy are an "unnecessary expense" with no proven benefits for most well-nourished women or their babies, said a review of science data.
Sold at about 18 euros ($20) per month, these supplements are heavily marketed to women in all stages of pregnancy as a means of warding off health problems, said the analysis.
Pregnant women are a soft target for products which promise to give their baby the best start in life "regardless of cost", said the authors.
And while daily doses of a B vitamin called folic acid, and vitamin D to a lesser degree, are known to be beneficial, there is no evidence that cocktails stuffed full of other vitamins are protective.
Some may even be harmful, said the paper: high doses of vitamin A can harm a developing foetus.
Multivitamin and mineral supplements typically contain 20 or more active ingredients.
"We found no evidence to recommend that all pregnant women should take prenatal multi-nutrient supplements beyond the nationally (British) advised folic acid and vitamin D supplements, generic versions of which can be purchased relatively inexpensively," said the review authors.
The analysis was published in the Drug and Therapeutics Bulletin, which informs British doctors and pharmacists about treatment and disease management.
The focus, said the paper, should be on promoting a healthy diet and boosting access to folic acid supplements for lower income women.
"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 authors wrote.
The team had reviewed published research on folic acid, vitamin D, iron, vitamins C, E and A, and multivitamin supplements in a review of official British guidelines for pregnant women.
The guidelines recommend 400 microgrammes of folic acid daily until 12 weeks of pregnancy, and 10 microgrammes of vitamin D throughout pregnancy and breastfeeding.
Much of the evidence on which marketing claims are based, come from studies in low-income countries where pregnant women are more likely to be malnourished, said the authors.
Folic acid, a synthetic version of folate, is used to fortify flour and bread to reduce birth defects of the brain, spine or spinal cord -- so-called neural tube defects.
Vitamin D is found in some foods and can be synthesised by the body when the skin is exposed to ultraviolet light. It has been linked to a healthy heart and bones.