Healthy pregnant women should think twice before taking iron supplements, say researchers who have linked high doses to blood pressure problems.
Iron is often given to combat anaemia in pregnancy, but many women take extra iron, on its own or in a multivitamin.
The Iranian university study, published in the British Journal of Obstetrics and Gynaecology, gave some women a 30mg daily dose as part of its research.
UK experts say that this amount should only be taken on GP advice.
The UK Food Standards Agency says that lower doses in UK multivitamins are unlikely to harm women.
Anaemia is a common condition in pregnant women, which, if left unchecked, can contribute to premature births and low birthweight babies.
It is caused by a lack of red blood cells, and taking iron on prescription helps the body produce more.
The researchers from Tarbiat Modarres University wanted to check the effect of iron supplements on women whose red blood cell level was normal.
They gave 370 women a 150mg dose of ferrous sulphate, which equates to approximately 30mg of actual iron, every day throughout their pregnancy.
A similar number of women were given a "placebo" dummy pill containing no iron.
Source - BBC