Babies born to mothers with mild anemia during pregnancy had smaller brains at age 2, study finds

Babies born to mothers who had anemia during pregnancy had smaller brains around age 2 compared with their peers, a new study has found — even though most cases involved only mild anemia.

A research team led by Jessica Ringshaw and Kirsten Donald at the University of Cape Town in South Africa recently published findings in the international journal Brain Communications, based on repeated brain scans of hundreds of South African infants tracked from birth to 24 months.

Anemia is a condition in which the blood lacks sufficient hemoglobin to carry oxygen. When a pregnant woman develops anemia, less oxygen reaches the fetus — and the brain, the organ that consumes the most oxygen, is the first to be affected.

In a report last year, the World Health Organization (WHO) said anemia among women of reproductive age had not declined in 20 years. It added that an international target to halve the rate by 2030 would be difficult to meet at the current pace.

The research team recruited 394 mother-infant pairs from a community on the outskirts of Cape Town, South Africa, and scanned each infant's brain five times between 3 and 24 months of age.

Babies born to mothers who had anemia during pregnancy had a total intracranial volume 3.77 percent smaller than those born to mothers without anemia.

Among specific brain regions, the corpus callosum showed the largest difference. This bundle of nerve fibers connects the left and right hemispheres and serves as the main channel through which the two sides of the brain exchange information. It was 4.39 percent smaller around 12 months, and the gap widened to 6.27 percent by 24 months.

The putamen, which is involved in movement and learning, was 3.32 percent smaller. The caudate nucleus, which helps form habits and regulate behavior, was 3.70 percent smaller at 18 months and 4.29 percent smaller at 24 months.

Brain scans taken at 3 and 6 months showed no meaningful difference in volume between the two groups. Differences began to emerge around 12 months and grew larger as the infants aged.

The research team offered two hypotheses to explain why the gap did not appear until after the first year.

According to the team, the first year of life is when the brain grows most rapidly, with different regions expanding at different rates. During this period, the overall pace of growth may be large enough to mask small differences. Once growth slows and stabilizes after 12 months, pre-existing gaps may become more apparent, the researchers said.

The team also raised the possibility that iron stores accumulated by the fetus in the womb may have served as a buffer. Breast milk contains highly absorbable iron, which could help offset any deficit during the first year. The researchers suggested that once those reserves ran out around the first birthday, the differences may have become visible.

However, neither hypothesis was confirmed by this study.

The most common cause of anemia is iron deficiency, and about half of the anemia cases among pregnant women in this study were attributed to it.

Yet when the researchers compared infants born to mothers with iron-deficiency anemia against those born to mothers without it, no difference in brain volume was found.

This suggests the brain size differences were linked to anemia caused by other factors, not iron deficiency itself.

The research team noted that the high prevalence of chronic infectious disease among pregnant women in the study region could be a contributing factor. Prolonged inflammation prevents stored iron from being mobilized, meaning iron supplements alone may not resolve anemia in such cases.

The total iron needed throughout pregnancy is about 1 gram — roughly half goes toward building the mother's blood supply, and the other half is directed to the placenta and fetus. In South Korea, anemia screening is conducted early in pregnancy once it is confirmed, with a follow-up check around weeks 28 to 30. All pregnant women are advised to take iron supplements from 20 weeks onward as a preventive measure.

The research team said managing anemia properly throughout pregnancy matters more than simply taking iron supplements. They added that the underlying cause of anemia should be investigated alongside any supplementation.

The findings are consistent with earlier research. Previous studies tracking other groups of children also found that those born to mothers with anemia during pregnancy had smaller brain regions. At ages 2 to 3, the corpus callosum was 7 to 8 percent smaller and the caudate nucleus 5 to 6 percent smaller, with the differences persisting through ages 6 to 7.

However, the research team acknowledged a key limitation: the study compared groups with and without anemia during pregnancy and cannot establish that anemia directly caused the differences in brain size.

DOI: 10.1093/braincomms/fcag318

Paper information: Jessica E Ringshaw, Michal R Zieff, Niall J Bourke, Chiara Casella, Layla E Bradford, Simone R Williams, Donna Herr, Marlie Miles, Carly Bennallick, Khula South Africa Data Collection Team, Sean Deoni, Jonathan O'Muircheartaigh, Dan J Stein, Daniel C Alexander, Derek K Jones, Steven C R Williams, Kirsten A Donald, Antenatal maternal anaemia and infant brain structure: high-field (3 T) and ultra-low-field (64 mT) MRI findings from South Africa, Brain Communications, Volume 8, Issue 5, 2026, fcag318.