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Oxygen test in pregnancy and childbirth
Medical expert of the article
Last reviewed: 08.07.2025
Methodology. For 10 minutes, the fetal heartbeat is counted or recorded during pauses and during contractions at 2-minute intervals. Then, for 15 minutes, continuous inhalation of 100% oxygen is performed using a sealed mask. After 15 minutes, the oxygen supply is stopped and the fetal heartbeat is counted again, but at 1-minute intervals to detect changes in the fetal heart rate if the fetus suffers from hypoxia. In cases where the fetus experiences hypoxia of varying degrees, stopping the oxygen supply leads, most often in the 4th to 6th minute, to changes in the heart rate. It is important to note that according to modern concepts, when oxygen is given, endogenous antioxidants are the preferred means of oxygen detoxification in various animal species and humans and a means of preventing cell damage caused by hyperoxia, especially with prolonged exposure.
When analyzing the curves of cardiotocograms obtained during the oxygen test, 3 main types were identified. The curves of the first two types indicate the most favorable prognosis for the fetus (fetal tachycardia) and the most unfavorable 3rd type of curve - bradycardia in the fetus - 100 beats/min or less.
Thus, the oxygen test allows us to judge the compensatory capabilities of the fetus and thereby avoid unnecessary surgical intervention or promptly begin therapy or surgical intervention depending on the degree of fetal hypoxia and the conditions necessary for rapid delivery.
Determination of intratissue PO2 from the skin of the fetal head. It has been established that the use of polarographic determination of PO2 in tissues is a very valuable additional method for determining the fetus's condition during labor, since it allows diagnosing intrauterine hypoxia at earlier stages and more accurately than using cardiomonitoring. A number of authors have found a high correlation between PO2 in the tissues of the fetal head, PO2 in the umbilical cord blood and the pH values of the tissues of the head. A high correlation has also been found between PO2 and the nature of labor, in particular the duration and intensity of contractions and the intervals between uterine contractions. Coordinated labor is of great importance for fetal oxygenation, especially the duration of intervals between uterine contractions, since relaxation of the myometrium during pauses between contractions ensures normal blood perfusion in the intervillous space and oxygen transport to the fetus.
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