That earlier study strengthened the case for supplements, but Christian's new research shows an even longer term impact on children who received iron in utero. She and her colleagues returned to Nepal, and were able to test the neurological development on children who were now on the brink of adolescence.

"The offspring of the mothers who had received iron and folic acid during pregnancy through three months postpartum had improved intellectual functioning including improved working memory and inhibitory control, which are domains capturing executive function, and they had better fine motor functioning ability as well."

Christian adds there was a qualitative difference between these older children and those whose mothers had received the supplements without iron.

She says these outcomes should remove any doubts lingering in the minds of health planners about whether or not to spend extra dollars to make sure that each pregnant woman receives iron supplementation during pregnancy. And she says in places such as the Asian subcontinent - where iron deficiency is endemic - supplementing with iron delivers an even larger bang for the public health buck.

Christian's research appears in the Journal of the American Medical Association.