Both high and low maternal hemoglobin levels raise newborn health risks: Study

A population-based study of over 1.1 million births in Ontario, CA found that both low and high maternal hemoglobin levels early in pregnancy are linked to higher rates of neonatal illness and death compared to those with mid-range levels.

The results are consistent with prior studies showing a relation between both low and high maternal hemoglobin concentrations and adverse neonatal outcomes. The study is published in Annals of Internal Medicine.

Researchers from the University of Toronto and colleagues set out to understand how early pregnancy hemoglobin levels affect newborn health in high-income countries. They analyzed hemoglobin measurements taken between 2 and 12 weeks of gestation for 1.1 million births from women aged 18 to 50 from 2007 to 2023.

They examined the association between hemoglobin concentration and severe neonatal morbidity and mortality (SNM-M), a composite measure of major conditions and critical interventions within 27 days of birth.

The study found that babies born to mothers with very low or very high hemoglobin were more likely to experience serious health problems, suggesting that both anemia and excess red blood cells can be harmful. The authors recommend further trials to assess whether iron therapy can improve outcomes.

Reference:

Ieta Shams, Grace H. Tang, Xuesong Wang, et al. Hemoglobin Concentration in Early Pregnancy and Severe Neonatal Morbidity and Mortality: Population-Based Cohort Study. Ann Intern Med. [Epub 3 February 2026]. doi:10.7326/ANNALS-25-02586