Accuracy and Utility of a New Reflectance Pulse Oximeter for Fetal Monitoring during Labor

Objective. To evaluate the accuracy of a new pulse oximeter inestimating the oxyhemoglobin (O₂Hb) concentration in fetalarterial blood (SaO₂) with either a high concentration ofhemoglobin F (HbF) or a low concentration of O₂Hb duringlabor. Patients and Methods. Fetal forehead arterial oxygenation wasdetermined in 44 fetuses by reflectance pulse oximeter (SpO₂)during labor and was compared with SaO₂ determined immediatelyafter birth. Because HbF has little or no known effect on pulse oximetry, butdoes affect the laboratory multiwavelength CO-oximeter typereading, the SaO₂ was corrected by HbF concentration.SpO₂ and SaO₂ were simultaneously measured infive hypoxic adult volunteers achieved by inhaling 11% oxygen. Results.A gradual decline in HbF concentration was seen during weeks 37 to 40 ofgestation. HbF concentration varied near term, ranging between 53 and 88% ofthe fetal hemoglobin concentration (mean ± SD = 74.6 ± 6.3%).This alteration produced a lower %O₂Hb percentby 4% at the most. The corrected SaO₂ in cord blood correlatedwith fetal SpO₂ (y = 0.974, x –7.279, r = 0.90). In five adults, SpO₂ reflected wellSaO₂ with a mean ± SD of bias of –1.1 ± 2.9%. Conclusions.SpO₂ determined by a new reflectance pulse oximeter at theend of labor correlated with an immediate post-natal cord arterial bloodsample before the first breath, with a mean and SD of bias of 8.5 ±6.2%. Reflectance pulse oximetry is a useful tool for continuousnoninvasive monitoring of the fetal oxygen status during labor.