The relationship between maternal anemia and umbilical cord oxygen content at delivery

Background: Anemia is one of the most commonly diagnosed comorbidities in pregnancy and is known to increase the risk of obstetrical complications. However, little is known about the effect of anemia on placental oxygen transfer and fetal oxygenation. Objective: This study examined the relationship between maternal anemia and fetal oxygenation status at delivery as measured by umbilical cord partial pressure of oxygen. Study Design: This is a secondary analysis of a prospective cohort study of singleton term deliveries with universal admission complete blood count and umbilical cord gases between 2010 and 2014. Maternal anemia was defined as hemoglobin of ≤10 g/dL on admission. The primary outcomes were umbilical artery and vein partial pressure of oxygen; the secondary outcomes were acidemia (umbilical artery pH of <7.1), hypoxemia (umbilical artery or umbilical vein partial pressure of oxygen at the <5th percentile), and hyperoxemia (umbilical artery/umbilical vein partial pressure of oxygen at the >90th percentile). Outcomes were compared between patients with and without anemia. Results: Maternal anemia was associated with a significantly higher umbilical artery partial pressure of oxygen (median [interquartile range], 20 [16–24] vs 19 [15–24] mm Hg; P=.01) and umbilical vein partial pressure of oxygen (median [interquartile range], 30 [25–36] vs 29 [23–34] mm Hg; P<.01). Neonates born to anemic mothers were more likely to have umbilical vein hyperoxemia (15.7% vs 10.9%; adjusted odds ratio, 1.51; 95% confidence interval, 1.26–1.81) with no difference in umbilical artery hyperoxemia. There was no difference in the rates of umbilical artery or umbilical vein hypoxemia. Although maternal anemia was associated with a significant difference in umbilical artery pH (7.28±0.060 vs 7.27±0.065; P<.01), there was no difference in the rate of neonatal acidemia between groups (1.6% vs 1.9%; adjusted odds ratio, 0.93; 95% confidence interval, 0.55–1.55). Conclusion: Umbilical cord oxygen content is higher in anemic mothers. Maternal anemia may lead to adaptations in maternal, placental, and fetal physiology, allowing for easier unloading of oxygen to the placenta and increased oxygen transfer to the fetus.