What parameter is normally lower in the fetus than in the mother during the second trimester: hemoglobin concentration, affinity of hemoglobin for oxygen, erythrocyte binding of 2,3-bisphosphoglycerate (2,3-BPG), cardiac output per kilogram body weight, or cardiac glycogen content?

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From the Research

The answer is b. Affinity of hemoglobin for oxygen. Fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin (HbA), which is essential for facilitating oxygen transfer from maternal to fetal circulation across the placenta, as noted in a study published in 2021 1. This increased affinity is due to structural differences in fetal hemoglobin, which has two gamma chains instead of the beta chains found in adult hemoglobin. Importantly, fetal hemoglobin has a reduced interaction with 2,3-BPG (2,3-bisphosphoglycerate), which normally decreases hemoglobin's affinity for oxygen.

Key Points

  • Fetal hemoglobin concentration is actually higher than maternal levels
  • Fetal erythrocytes bind more 2,3-BPG, as discussed in a study on 2,3-bisphosphoglycerate metabolism in human erythrocytes 2
  • Fetal cardiac output per kg is higher due to higher metabolic demands
  • Cardiac glycogen content is greater in the fetus as a reserve for the stress of birth

Evidence Review

The most recent and highest quality study on this topic was published in 2021 1, which found that fetal hemoglobin has a significantly higher affinity for oxygen than adult hemoglobin. This study used near-infrared spectroscopy to measure tissue oxygenation in preterm and term neonates. Other studies, such as those published in 1999 2, 1989 3, 1983 4, and 1994 5, also provide insight into the metabolism and function of fetal hemoglobin, but the 2021 study is the most relevant and recent.

Clinical Implications

Understanding the differences in hemoglobin affinity for oxygen between fetal and adult hemoglobin is crucial for managing fetal and neonatal care, particularly in cases of anemia or hypoxia. The higher affinity of fetal hemoglobin for oxygen ensures that the fetus can extract oxygen from the maternal circulation efficiently, even in low-oxygen conditions. This knowledge can inform clinical decisions regarding oxygen therapy and blood transfusions in neonates.

References

4
Research

Role and induction of 2,3-bisphosphoglycerate synthase.

Molecular and cellular biochemistry, 1983

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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