Iron deficiency affects one in five of the world's population and is more prevalent in pregnant women, say researchers. Thyroid disorders and iron deficiency (ID) are associated with obstetrical and fetal complications in expecting mothers. The finding showed that iron deficiency increases the risk of having a thyroid disorder as well as raises complications such as miscarriages and pre-term births.

Iron is essential for the normal functioning of thyroid peroxidase (TPO-abs) - a protein essential for the proper functioning of the thyroid. Pregnant women need to make enough thyroid hormone for the full development of their babies' brains, which is particularly critical during the first semester when the fetus has not developed a thyroid gland of its own, said the paper.

Iron deficiency also causes thyroid autoimmunity - a disease where the immune system mistakenly destroys healthy thyroid cells; causing thyroid hormone levels to fall. It can be especially dangerous for pregnant women.

For the study, the team followed 1900 pregnant women who were in their first trimester. They measured women's blood ferritin, an indicator of iron deficiency, thyroid hormone free thyroxine (FT4) and thyroid hormone thyroid stimulating hormone (TSH).