Pricey multivitamins marketed to pregnant women are a waste of money, a new study has concluded.
And some, particularly those containing vitamin A, may even be harmful to the foetus.
Drug and Therapeutics Bulletin, a journal associated with the British Medical Journal, reviewed published research on popular vitamin supplements for pregnant women. They commonly contain a range of ingredients, including vitamins B1, B2, B3, B6, B12, C, D, E and K, folic acid, iodine, magnesium, iron, copper, zinc and selenium.
But the research suggests all mothers-to-be need to top up on is folic acid and perhaps vitamin D - at least in advanced Western countries like the UK, where the study was conducted, or New Zealand.
"We found no evidence to recommend that all pregnant women should take prenatal multi-nutrient supplements beyond… folic acid and vitamin D supplements, generic versions of which can be purchased relatively inexpensively," the authors wrote.
In New Zealand, multivitamin supplements aimed at pregnant women can cost upwards of $25 a month - money the researchers say would be better spent elsewhere.
Vitawomenz, sold at fertilityhealth.co.nz for example, contains not just folic acid and vitamin D, but magnesium, zinc, copper, selenium, biotin, omega 3 and vitamins E, K, C, H, B1, B2 and B12. Radiance Multi for Pregnancy, for sale at mynaturalhealth.co.nz, contains all that and beta-carotene (which the body turns into vitamin A), boron, chromium, potassium, vanadium, phosphorus and more.
"Much of the evidence on which the marketing claims for multivitamin supplements are based, comes from studies carried out in low-income countries, where women are more likely to be undernourished or malnourished than women in the UK," the study claims.
"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 study says pregnant women may be particularly sensitive to marketing because they want to give their child "the best start in life, regardless of cost".
The only supplement that showed a clear clinical benefit was folic acid, which helps prevent neural tube defects. The evidence for vitamin D wasn't quite as strong.
The New Zealand Ministry of Health recommends taking between 800mcg and 5mg of folic acid from four weeks before conception to 14 weeks after. It also recommends topping up on iodine (which wasn't examined at in the latest study) and vitamin D.