A study has found that women who take iron tablets while pregnant give birth to smaller babies
Pregnant women are being warned not to take iron supplements unless they are anaemic after a study found those who take them are more likely to deliver smaller babies.
The Food Standards Agency already recommends that pregnant women get iron from their diet, rather than supplements.
In the past, iron has been recommended in pregnancy to help promote growth of the placenta and baby.
Research published in BJOG: An International Journal of Obstetrics and Gynaecology, found that iron supplements also increase the risk of copper and zinc deficiency in women.
The Iranian study followed 727 women who were not anaemic, of whom 370 were given a 150mg ferrous sulphate (iron preparation) tablet every day throughout pregnancy, while 357 were given a dummy pill.
They were then examined during pregnancy and for six weeks after delivery.
Researchers, from Tarbiat Modarres University in Tehran, found that women taking the tablets are more likely to develop high blood pressure and more likely to have a small baby.
Professor Philip Steer, BJOG editor-in-chief, said: "Anaemia in women is often associated with low birth weight and preterm births, but that does not mean that women should be popping iron pills, or any vitamin pills indiscriminately, to prevent poor pregnancy outcomes.
"Women who are not suffering from anaemia should ensure that they receive proper advice on diet and nutrition from their doctors and midwives."