The first-line method for evaluating fetal oxygenation during labor is electronic fetal heart rate (FHR) monitoring. Despite the extensive use of FHR monitoring during labor, it has poor specificity, and its sensitivity is 85 percent. This means that a high number of FHR tracings are nonreassuring even when the fetus is in good condition. Until recently, the only adjuvant to assessing fetal hypoxia and acidosis was fetal scalp sampling. The drawbacks to fetal scalp sampling are that it is invasive and traumatic to the fetus, can only assess the fetus on an intermittent basis, and can be inaccurate if contaminated with amniotic fluid or caput succedaneum. Fetal pulse oximetry was developed as a less traumatic and invasive method of assessing fetal oxygenation. It allows for real-time and continuous assessment of the fetus. Kühnert and Schmidt evaluated the use of fetal pulse oximetry during labor and compared it with FHR monitoring and fetal scalp sampling.

The trial was a randomized prospective study of women in labor who had nonreassuring FHR patterns as defined by the International Federation of Gynecology and Obstetrics scoring system. All patients had term, single-fetus pregnancies; cephalic presentations with active labor at two centimeters dilatation; at least −2 station; and a nonreassuring FHR pattern. The initial assessment was done using fetal scalp sampling on all of the participants, who were then randomly assigned to two groups. Group one received fetal pulse oximetry, and group two served as a control. The main outcome measures were number of operative deliveries (see accompanying table) and number of fetal scalp samples. Adverse maternal and neonatal outcomes were measured, as were metabolic acidosis and the need for resuscitation in the neonate.

There were 146 women included in the study. There was a significant reduction in the number of operative deliveries in the group that were assessed using fetal pulse oximetry when compared with the control group. There was also a significant reduction in the need for fetal scalp sampling in the fetal pulse oximetry group compared with the control group. There was no difference between the two groups in adverse maternal or fetal events. In addition, there was no difference between the groups in fetal metabolic acidosis or the need for resuscitation.

The authors conclude that fetal pulse oximetry does reduce the number of operative deliveries and the need for fetal scalp sampling in term pregnancies when there is a nonreassuring FHR pattern. They add that fetal pulse oximetry during active labor provides a more accurate assessment of fetal well-being and may reduce the need for interventions.