Intrauterine Asphyxia: Clinical Implications for Providers of Intrapartum Care

Jenifer Fahey, CNM, MSN, MPH; Tekoa L. King, CNM, MPH


J Midwifery Womens Health. 2005;50(6):498-506. 

In This Article

Maternal-Fetal Gas Exchange

Several adaptive mechanisms facilitate transfer of gases between maternal and fetal circulation. The partial pressure of oxygen in maternal circulation is higher than in fetal circulation, which facilitates maternal-to-fetal transfer of oxygen via diffusion across the placental membranes. In addition, respiratory changes during pregnancy decrease the partial pressure of carbon dioxide (PCO2) in maternal circulation; thus, the transfer of carbon dioxide from fetus to mother is facilitated. The fetus has adaptive mechanisms that support function and growth in a low-oxygen environment; fetal blood has more hemoglobin than adult blood, and fetal hemoglobin has a higher affinity for oxygen than maternal hemoglobin at the same partial pressures of oxygen. In addition, fetal circulation "overperfuses" certain organs such as the brain.[7] Furthermore, relative to an adult, the fetus has an increased number of capillaries, increased cardiac output, and a higher heart rate.


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