The efficacy of intrapartum fetal surveillance when fetal pulse oximetry is added to cardiotocography

Fetal pulse oximetry: correlation with intrapartum fetal heart rate patterns and neonatal outcome

AIM

To determine how fetal pulse oximetry behaves in various cardiotocographic (CTG) tracings and correlates with neonatal outcome.

PATIENTS AND METHODS

Pregnant women undergoing active labor with singleton pregnancies of 32-42 weeks were enrolled. CTG recordings were reassuring or nonreassuring (namely variable or persisting late decelerations). Pulse oximetry values during labor and changing throughout deceleration and recovery phases, duration and frequency of pulse oximetry recordings <30%, and neonatal outcome were determined. One-way anova, Tukey test, chi(2)-test and multiple logistic regression model were used for statistical analysis where appropriate.

RESULTS

A total of 156 pregnant subjects were divided into three groups: reassuring fetal heart rate (FHR) patterns (group 1, n=78 [50%]), late decelerations (group 2, n=16 [10.3%]) and variable decelerations (group 3, n=62 [39.7%]). The initial and final pulse oximetry readings, pulse values in first stage of labor, the duration and the frequency of pulse oximetry recordings <30% were significantly different between groups (P<0.001, P<0.001, P<0.001, P=0.001, P<0.001). Fetal acidosis was significantly more frequent with late decelerations (23.1%, P=0.004). A multiple logistic regression model demonstrated that the initial pulse oximetry value during active labor was the most predictive variable of neonatal well-being (P<0.001).

CONCLUSION

Decreased fetal pulse oximetry values, especially prolonged and recurrent recordings <30% are well-correlated with abnormal FHR patterns, indicating an association with fetal compromise and metabolic acidosis. Going through active labor with a lower initial value of FSpO(2) more frequently leads to an altered FHR pattern and subsequent adverse fetal outcome.

How well does reflectance pulse oximetry reflect intrapartum fetal acidosis?

OBJECTIVE

The purpose of this study was to determine the sensitivity and specificity for acidosis of intrapartum fetal oxygen saturation measured by reflectance pulse oximetry.

STUDY DESIGN

Intrapartum fetal oxygen saturation values per labor stage were correlated with umbilical artery pH, base excess and PCO(2) by regression analysis. Receiver operating characteristic curve analysis was performed with the use of historic umbilical arterial cutoff values; a fetal oxygen saturation cutoff range with optimal sensitivity and specificity was calculated.

RESULTS

Mean fetal oxygen saturation was 42.8%, over the mean 132 minutes of 107 recordings. Overall areas under the sensitivity and specificity curves were 0.77 for pH and PCO(2), decreasing sharply toward birth; all areas for base excess were poor (approximately 0.5). Depending on stage and umbilical artery parameter, fetal oxygen saturation cutoffs were 33% to 36%, with sensitivities of 0.67 to 0.8 and specificities of 0.62 to 0.90.

CONCLUSION

Fetal oxygen saturation sensitivities and specificities for acidosis do not yet justify the supplementation of cardiotocography with routine reflectance pulse oximetry.

Intrapartum cardiotocography and fetal pulse oximetry in assessing fetal hypoxia

OBJECTIVES

A retrospective analysis of short-term variability (STV), a cardiotocography (CTG) parameter, in relation to fetal blood saturation values (FSpO(2)) obtained by fetal pulse oximetry.

METHODS

The study included 26 healthy pregnant women monitored continuously during delivery with both cardiotocography and fetal pulse oximetry.

RESULTS

Lower FSpO(2) values were observed in the group showing STV levels <or=6.0 ms in the 1st stage of labor (44.7+/-3.46% vs. 49.2+/-1.8%), but this result was not statistically significant. In the 2nd stage of labor, FSpO(2) values in the group with STV levels <or=6.0 ms were significantly lower than those with STV levels >6.0 ms (34.4+/-2.9% vs. 43+/-7.2%; P<0.001). A positive correlation was found between STV levels <or=6.0 ms and mean FSpO(2) values in the 2nd stage of labor.

CONCLUSIONS

1. A significant relationship was observed between short-term variability in the cardiotocographic records and fetal blood saturation levels in the 2nd stage of labor. 2. Fetal pulse oximetry can be valuable in assessing fetal wellbeing, especially when CTG records are abnormal.

Intrapartum fetal pulse oximetry. Part 2: Clinical application

Part II continues by discussing the clinical application of fetal pulse oximetry in intrapartum fetal surveillance as reviewed in the literature. It profiles the predictive ability of fetal pulse oximetry and its correlation with conventional methods of fetal monitoring. In addition, an account is made of its limitations, safety, and acceptability in clinical practice.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians

LEARNING OBJECTIVES

After completion of this article, the reader will be able to describe the predictive abilities of fetal pulse oximetry and its correlation with conventional methods of fetal monitoring, to define the critical threshold of fetal oxygen saturation, and to summarize the safety of fetal pulse oximetry.

Continuous intrapartum pH, pO2, pCO2, and SpO2 monitoring

The goal of intrapartum surveillance and its further development is better patient care for both the fetus and the gravida. A normal FHR pattern is usually associated with the delivery of a normal well-oxygenated infant; however, a nonreassuring FHR is not always associated with the delivery of a compromised infant. This situation has led to an increase in unnecessary obstetric interventions in the form of a rising cesarean section rate. Fetal scalp sampling was developed in an attempt to improve the predictive value of electronic FHR monitoring, but because this technique is not widely used, management decisions are frequently made using FHR patterns alone. Much research has been performed in the search for a continuous biochemical measurement of fetal status, including continuous pH, pO2, or pCO2 and various combinations of these methodologies. None of these measurements are used in current clinical practice, mainly owing to technical problems and difficulties associated with the continuous direct measurement of these parameters in fetal blood throughout labor. The promising new field of fetal pulse oximetry has the potential to provide reliable, meaningful, and reproducible data as shown in early cross-sectional studies and more recent longitudinal studies. By identifying developing hypoxia, this technology may reduce the uncertainty associated with electronic FHR monitoring. Fetal pulse oximetry may also provide critical information relating to the detection and management of the hypoxic fetus. Any new method of intrapartum fetal monitoring requires careful evaluation to assess its potential value before its introduction into clinical practice. The use of fetal SpO2 monitoring in the presence of a nonreassuring FHR pattern is being examined in a multicenter randomized controlled trial. This study will address the question of whether supplementary monitoring of fetal SpO2 levels can lead to a reduction in the cesarean section rate for fetal distress. The available data on fetal noninvasive pulse oximetry have been obtained from a combination of well-designed cohort studies (level II-2 evidence) or from earlier multiple time series (level II-3 evidence). The results from the US Multicenter Trial (level I evidence) should provide a significant addition to current evidence. A continuous fetal noninvasive monitor measuring fetal oxygenation directly could lead to an improvement in the sensitivity and specificity of fetal surveillance. This improvement could ultimately result in a reduction in unnecessary interventions by differentiating hypoxic fetuses from nonhypoxic fetuses and, more importantly, may lead to earlier intervention for fetuses in danger of serious compromise.