The OxiFirst™ Fetal Oxygen Saturation Monitoring System:
Frequently Asked Questions 

Mallinckrodt Inc. Healthy Mother and Baby

This section provides a compendium of the questions often asked about the OxiFirst System and it's use in providing reassurance (FSpO₂ > = 30%) during periods of non-reassuring fetal heart rate. Questions and answers regarding our products are posted in Frequently Asked Questions sections. If you have a question that needs answering, which has not already been answered in our FAQ's section, please email us at Expert@mkg.com and our trained professionals will do their best to respond promptly.

How do adult and fetal monitoring with pulse oximetry differ and what do these differences mean in terms of designing a fetal oximeter?

The underlying physics of the technology are actually quite similar. However, the uniqueness of the intrauterine environment presents a number of challenges for fetal oxygen saturation monitoring. The differences outlined below become significant factors in the design and use of the technology.

Sensor application sites are limited on the fetus in utero, and direct observation of sensor placement is not possible. Because the crown of the head is not optimal for monitoring, and since relatively strong fetal pulses can be found beyond the hairline on the fetal face, the cheek/temple area was chosen as the preferred application site for the OxiFirst Fetal Oxygen Sensor. Arterial pulse amplitudes on the fetal face are typically two to ten times smaller than those seen on adult fingers (the most common site used in adult monitoring). Thus, the electronic design of the OxiFirst fetal pulse oximetry system was optimized to work with very small pulses.

The fetal sensor has unique features designed for use in the intrauterine environment. A waterproof housing surrounds the sensor optics and electronics for proper functioning in the presence of amniotic fluid. Application of the sensor to the cheek/temple area of the fetal face requires the use of a noninvasive reflectance sensor. The emitters and photodetector of any reflectance-style sensor must be in constant contact with the underlying skin to prevent light-shunting measurement errors. Because the clinician cannot directly observe the fetal sensor during insertion and monitoring, two features were developed to aid in reliable sensor placement:

1) a special impedance measurement circuit provides feedback from the sensor to the monitor, showing whether or not there is adequate sensor contact with fetal skin (contact electrodes), and

2) a flexible tip helps to hold the sensor optics snugly against the fetal face between uterine contractions (fulcrum tip).

Fetal oxygen saturations are significantly lower than adult saturations. Conventional pulse oximeters have reduced accuracy at saturations below 85%. When saturation falls below 85% in non-fetal patients, an unhealthy condition is indicated and some form of intervention generally occurs. So, for conventional pulse oximeters, limited accuracy at low saturations does not affect the clinical utility of the system.^1,2 The OxiFirst Fetal Oxygen Saturation Monitoring system was designed and calibrated for monitoring of oxygen saturations below 70%, typical saturation levels seen in the fetus during labor.

How does the fetal sensor stay in place, and what does the sensor's fulcrum tip do?

The distal end of the sensor is inserted beyond the cervix and is captured between the fetal head and the uterus, with the cable traveling under the cervix and exiting through the birth canal. The sensor does not penetrate the fetal skin. The fulcrum is a smooth and flexible lever arm on the most distal end of the sensor that helps hold the sensor down against the fetal skin. It does this by taking up any remaining space between the fetal head and the adjacent uterine wall. The fulcrum flexes as the spacing between the fetus and the uterus varies, thus helping to assure continuous contact between the sensor and the skin - critical for accurate pulse oximetry measurements.

How do the system's contact electrodes work?

Smooth, gold-plated contact electrodes located on the front of the sensor are used to determine if the sensor is in positive contact with the tissue bed. The system measures the electrical impedance or opposition to current flow between these electrodes. If the measured impedance drops below a preprogrammed threshold, this indicates that the sensor is lifted. If the electrodes are surrounded by air, the measured impedance increases to levels significantly higher than wet skin values found in utero, and the system senses this as a removed (lifted) sensor. In utero, when the sensor is lifted, the impedance is low because the conductivity of amniotic fluid is high. Impedance increases significantly when the sensor is properly pressed onto the fetus' skin because the skin insulates the electrode from the surrounding fluid. The electrodes themselves are biocompatible and do not react with the amniotic fluid or the skin.

Is the impedance of hair and skin different?

Hair tends to act as a sponge for amniotic fluid. Because of this, fetal hair in utero has a much lower impedance than wet skin. When fetal hair is thick enough to allow the sensor's emitted light to shunt to the detector and affect the accuracy of the FSpO₂ reading, there is generally sufficient amniotic fluid trapped to yield a low impedance measurement (sensor lifted). If the fluid is squeezed out, or if excessive vernix coats the hair, then the impedance can mimic the values of contact with the skin. Placing the sensor on the cheek or temple area beyond the hairline minimizes the likelihood of these events.

How does the system determine fetal oxygen saturation?

The OxiFirst system determines fetal oxygen saturation by measuring the change in light levels caused by the pulsing arterial blood volume in the tissue. A ratio of the amplitude of these changes is made at two light wavelengths - in the far red and the near infrared. The amount of change in light levels for each qualified pulse are used to determine saturation. Pulses are qualified and distinguished from motion using a proprietary software algorithm which looks at various parameters associated with normal optical plethysmograms. Further explanation of saturation measurement may be found in Perinatal Reference Note Number 1.

What is meant by "registration time?"

This refers to the percentage of time that the fetal pulse oximetry system displays saturation values during labor. Registration time includes only the periods when the sensor is determined to be in contact with the skin and signal quality is sufficient for determining saturation.

How and why does the system perform signal averaging, and what does this mean clinically?

The system averages beat-to-beat calculations in the determination of saturation to reduce the effects of measurement noise and artifact. This signal processing method yields the most reliable indication of the fetus' saturation. Current published literature and laboratory evidence suggests that transient episodes of desaturation are less significant to fetal well-being than prolonged hypoxia, and that the response time of the system is more than adequate to reveal significant events.

What is the response time of the system to changes in saturation?

Response time is a measure of how long it takes for the displayed value of FSpO₂ to respond to a real change in arterial saturation. Two modes (slow and fast) are available to the user, both accessible from the front panel of the monitor. The slow mode (default) response time is approximately 120 accepted pulses or about 50 seconds at a heart rate of 150 bpm. This speed is recommended for routine use. The fast mode response time (Mode 2) is approximately 30 accepted pulses or about 11 seconds at 150 bpm.

The response time of displayed saturation depends on the heart rate and signal quality because the averaging that occurs in the calculation is updated based on accepted pulses of the plethysmogram. As the heart rate increases or decreases, the response time varies accordingly. In addition, when signal quality is poor, response time is longer due to fewer accepted pulses.

Why does the OxiFirst system use the 735-nm wavelength?

The 735nm wavelength light was selected for the red LED to improve the fetal pulse oximetry system's performance at low oxygen saturations.

The use of the 735-nm wavelength, when paired with 890 nm, results in a dramatically better balance between the two signals at the lower saturations typically seen in fetuses. Oxygen saturation readings become significantly less sensitive to normal physiological variations, such as tissue blood volume and pressure.^1,2

At high oxygen saturations (>85%), such as those typically seen in adult pulse oximetry, signal absorption by the tissue at 660 nm is well matched to that at 890 nm, and the conventional choice of wavelengths is generally superior to those chosen for fetal monitoring.

Why is fetal calibration important?

For accurate FSpO₂ measurement, it is important to calibrate the fetal pulse oximeter using methods that best represent the fetus in utero. This requires:

• the saturation range used in the calibration to be appropriate for fetal saturations
• tissue characteristics (known to influence pulse oximetry measurements) that mimic those of fetal tissue
• light absorption by oxygenated and reduced hemoglobin to be like that of fetal blood. A calibration matrix determined on adults at high oxygen saturations does not ensure accuracy at low saturations on the skin of a fetus.

How was the OxiFirst System calibrated?

A fetal oximeter must be empirically calibrated over a range of low oxygen saturations that cannot be safely or ethically obtained in breathe-down studies using adult human volunteers. Additionally, there is no practical way to reliably and repeatedly obtain arterial blood from a human fetus during labor to conduct such a study. Therefore, the OxiFirst system was calibrated in carefully controlled hypoxia studies in a laboratory animal model. This calibration was validated by data collected in a separate animal study conducted by independent investigators at a different site using a similar protocol.

Oxygen saturation readings obtained with the calibrated OxiFirst system were also compared to laboratory hemoximeter values in a series of critically ill infants and children with congenital heart disease or severe respiratory failure. The OxiFirst system is specifically designed and calibrated for use on the fetus with oxygen saturations less than 85%. Unreliable results can occur if used on adults or patients with higher oxygen saturations. See Perinatal Reference Notes Number 1 and 2 for further information about calibration.

How does FSpO₂ compare to laboratory hemoximeter SaO₂ and calculated SaO₂?

Data from the calibration studies (animals and infants/children) show good correlation between FSpO₂ obtained with the system and measured laboratory hemoximeter values of SaO₂ obtained from simultaneously drawn arterial blood samples. See Perinatal Reference Note Number 1 for further information. Calculated SaO₂ values from blood gas analyses are unreliable; consequently, the correlation to FSpO₂ is unreliable.

Hair can affect the pulse oximeter in two ways. First, light transmission is weakened when light is absorbed by hair, thus making it more difficult for the oximeter to obtain adequate signals. Second, hair may prevent the sensor from making intimate contact with the fetus' skin and, consequently, cause light shunts (see the earlier discussion regarding contact electrodes and hair). Placement of the sensor beyond the hairline reduces the likelihood of these two effects interfering with FSpO₂ readings.

How does the clinician know the system is monitoring fetal, not maternal, saturation?

Saturation readings above 85% are unlikely to be of fetal origin, and most likely reflect maternal information. 

The side of the fetal sensor with white numbers at 1 centimeter intervals (30, 29, 28..) should face toward the fetus. To verify that the system is monitoring oxygen saturation from fetal arterial pulses, the fetal heart rate can be checked by auscultation and the maternal pusle can be palpated. Compare the fetal and maternal heart rates with the optical pulse rate displayed by the FSpO₂ monitor to verify that fetal saturation is being monitored.

What is the effect of meconium, blood, or vernix?

Meconium-stained skin has an insignificant affect on fetal pulse oximeter readings. The effect of meconium-staining on light absorption does not change with pulsation so it is subtracted during signal processing in the same manner as is absorption due to venous blood. The same is true for blood and vernix. Typically, meconium and blood do not adhere to the sensor's contact electrodes or optical components, so they do not present a problem. However, if such materials are present in sufficient quantity to interfere with the normal operation of the "sensor lifted" indicator, optical shunting (light reaches the photodetector without passing through tissue) can occur and readings may be affected.

Does the presence of fetal hemoglobin affect the accuracy of FSpO₂ readings?

Fetal hemoglobin (HbF) does have a slightly different light absorption characteristic than adult hemoglobin, and can be expected to have some level of influence on FSpO₂ readings. As demonstrated with mathematical modeling⁴, fetuses with higher concentrations of HbF will usually cause the system to read slightly lower FSpO₂ values than fetuses with lower concentrations of HbF. However, due to differences in fractional HbF content, the relative difference in FSpO₂ readings is on the order of ± 1% and is not clinically significant.

Does sickle cell disease or thalassemia in mother or fetus affect the measurement of fetal oxygen saturation?

These hemoglobinopathies are inherited defects of hemoglobin resulting from impaired globin synthesis (thalassemia syndromes) or structural abnormality of the globin (hemoglobin variants). Under normal circumstances, the carrier states for the most important of these hemoglobinopathies, beta-thalassemia minor [HbA(a2 ß1 )] and sickle-cell hemoglobin (HbAS), are symptomless with no direct effect on the quality of life or life expectancy. During pregnancy, however, the clinical effects of these hemoglobin defects, even in the heterozygous or carrier state, vary widely which complicates obstetric management.⁵

In vitro pulse oximetry studies with sickle cell blood (U. S. National Institutes of Health ⁶), and several in vivo experiments on adults and children with sickle cell disease, were conducted to determine accuracy and reliability of arterial oxygen saturation measured with Nellcor technology. In these studies, conventional pulse oximetry measurements (660 nm/890 nm) were compared with simultaneous assessment of oxygen saturation by arterial blood gas measurement and oxygen dissociation curve analysis. Study results demonstrated that conventional pulse oximetry is an accurate and effective noninvasive method for monitoring oxygen saturation in the presence of sickle cell disease^6-8.

There have been no published clinical studies to date in which fetal oxygen saturation was monitored for patients suffering from either of these hemoglobinopathies. Except for the case of homozygous a-thalassemia major, the hemolytic anemia that often accompanies these diseases is not operational in utero or at birth since about 75% of the hemoglobin in the red cells at term is fetal hemoglobin (HbF).^9,10 One would predict, therefore, that in theory oxygen saturation values in affected fetuses would be similar to those of other normal, healthy fetuses if the mother is heterozygous for the trait and is in good health at delivery. A complete and definitive answer to this question warrants further clinical study.

Based on the changes in blood volume and relative differences in light absorption with the cardiac cycle, pulse oximeters measure the oxygen saturation of arterial blood, which is the only part of the vasculature that normally pulsates. Because tissue such as skin, bone and the venous vasculature are generally considered non-pulsating, they do not enter into the pulse oximeter's determination of oxygen saturation.

Skin pigmentation for conventional (adult) pulse oximetry can affect signal quality if it is so dark that it does not allow light from the light emitting diodes to pass into and out of the pulsating vascular bed. Melanotic pigmentation is not well developed in most fetuses irrespective of ethnic group and should not interfere with FSpO₂ readings.

Why is there an occasional transient rise in saturation values during contractions?

Some investigators have suggested that this event reflects a true transient rise in fetal saturation. It is more likely an artifact of pulse oximetry caused by blood being squeezed out of the tissue in the region under the sensor. Some light shunts through exsanguinated skin and tissue and reaches the photodetector, causing a measurement error. Earlier Nellcor sensor prototypes showed a higher incidence of this condition than the current model FS-14 Fetal Sensor, which has been redesigned to reduce these reading artifacts.

Direct observation of the sensor on the fetal face is not possible. After identifying fetal position in utero using abdominal palpation and by locating landmarks during a vaginal exam (the sagittal suture and one or both fontanels), the sensor is introduced and advanced until the "sensor lifted" indicator goes out. This is an indication that the sensor has made contact with fetal skin. The presence of pulsatile signals, a signal quality of seven or more illuminated segments, and continuous display of FSpO₂ are indications that the sensor is in proper position. For a comprehensive explanation of sensor insertion, see the Fetal Oxygen Sensor Placement Guide.

Can the mother get up and walk around?

Fetal pulse oximetry is indicated for use in patients who have a nonreassuring fetal heart rate pattern during labor. Generally, those patients require close surveillance of fetal status. If the mother were to walk beyond the length of the patient module cable, it would be necessary to disconnect the sensor from the system, thereby interrupting the acquisition of fetal saturation information. At present, remote monitoring with fetal pulse oximetry is not technically feasible.

Additionally, ambulation may cause the sensor to slip from the preferred monitoring site, thereby requiring an adjustment to the sensor. Also, if the mother were ambulatory, it is possible that motion artifact may disrupt the acquisition of saturation data.

Are saturation values the same over all areas of the fetal face?

A working assumption in pulse oximetry is that arterial oxygen saturation is essentially uniform throughout the arterial tree, assuming there is adequate flow. Some sensor designs, however, can result in saturation readings that are sensitive to the histological environment in the region underneath and near the sensor. The OxiFirst fetal sensor has been designed to minimize this artifact, resulting in FSpO₂ readings that are less sensitive to where the sensor is located (within the accuracy specifications of the system).

What is the normal range of oxygen saturation of the fetus during labor?

Information available regarding the "normal" range of fetal arterial oxygen saturation during labor comes from laboratory studies conducted on animals and from fetal pulse oximetry studies on humans. Animal studies, in which preductal arterial blood samples are drawn, find normal fetal saturations range from 30% to 70%. Even when the maternal ewe is ventilated with 100% oxygen, fetal saturations have not exceeded 86% under stable conditions¹¹. For humans, in a series of 87 normal labors with normal outcomes, the mean FSpO₂ was 47% (+8.4%). Using prototype designs on humans, investigators have noted a steady decline in baseline saturations as labor progresses, generally 5% to 10% from early to late labor.^12,13

Why do some researchers report different ranges of "normal?"

Investigators using different prototype systems have reported saturation values from the fetal head observed during labor. The reported ranges fall between 30% to 100%, but not all systems were empirically calibrated over the full range of fetal saturation as was the OxiFirst system, nor were they free from measurement artifact.^14-20

What is the critical threshold of oxygen saturation for the fetus?

Published animal studies suggest that fetal imbalance, as indicated by the onset of metabolic acidosis, may begin when preductal saturation is between 25% and 35%.^21-23 These studies find that there is no sign of hypoxia when saturation exceeds 35%.

A prospective multicenter human observational study in Germany was undertaken to quantify the predictive agreement between FSpO₂ and fetal scalp pH when used to assess fetal status during periods of nonreassuring fetal heart rate patterns during labor. The results of 50 pairs of FSpO₂ readings and simultaneous scalp pH values from 46 patients (one patient contributed 5 data pairs) demonstrated that setting the critical threshold value of FSpO₂ at 30% yielded a reasonable balance between sensitivity and specificity for the prediction of fetal acidosis (defined as scalp pH < 7.20).²⁴

The primary goal of fetal oxygen saturation monitoring is to improve the overall specificity of diagnosis in the context of an already nonreassuring, and thus, highly sensitive FHR pattern. Setting the critical threshold at 30% results in an overall sensitivity of 83% and a specificity of 100%. A comprehensive discussion of the evidence for a fetal SpO₂ critical threshold of 30% can be found in Perinatal Reference Note Number 2.

What is the correlation between FSpO₂ and pH, and outcome?

Much of the clinical data available in the literature comes from early prototype systems that have not been calibrated and may contain data biased by artifact. Nonetheless, several studies show significant correlation between FSpO₂ readings and blood gas values obtained from scalp samples or cord blood.^25-29 The prospective multicenter human observational study con-ducted in Germany further demonstrated that an FSpO₂ of greater than 30% was predictive of a scalp pH of greater than 7.20. ²⁴

Can the system be used before the rupture of membranes?

Prior to rupture of membranes, the sensor cannot make intimate contact with the skin of the fetus. Accurate pulse oximetry measurements can only be obtained if the sensor light that reaches the photodetector is restricted to that light which has traveled through blood-perfused tissue (i.e., no shunts). Optical pulses can, under some conditions, be observed with the membranes intact, but FSpO₂ readings cannot be considered reliable.

How do dilation and station affect the system?

The fetal sensor is easiest to place after the cervix has reached a dilatation of 2 cm or greater. When the fetal head is high (above -2 station), the sensor is difficult to locate in a region which assures constant sensor-fetal skin contact. Saturation readings can be obtained more easily after the head drops below -2 station.

During the second stage of labor there may be an increased frequency of intermittent FSpO₂ signal loss requiring sensor adjustment.

Does the system register during contractions?

The OxiFirst system generally can obtain readings during contractions. However, at the peak of some intense contractions, fetal SpO₂ information may not be displayed. It is believed this is because intrauterine pressure rises to a level where fetal pulses under the sensor can become too small to be detected. When intrauterine pressure subsides, fetal pulses can again be measured.

Sometimes the change in maternal and fetal position during a contraction can cause the sensor to lose contact with the skin, and then recover when the contraction has passed. Additionally, there may be significant motion artifact during this period, which makes recognition of the fetal plethysmogram more difficult.

Does use of the system require epidural anesthesia?

Most women do not experience discomfort with sensor placement. The sensation is similar to that felt during a vaginal examination. However, since each woman in labor has a different pain threshold, the decision regarding epidural anesthesia should be individualized to the patient's needs and medical requirements.

Is the OxiFirst system easy and convenient to use?

Minimal training is required to operate the OxiFirst Fetal Oxygen Saturation Monitoring system. Physicians and other licensed practitioners who use the OxiFirst system should have demonstrated expertise in determining fetal presentation and head position. Insertion of the sensor is similar to that of an intrauterine pressure catheter. Most clinicians feel confident with the procedure after the placement of 2 to 4 sensors. As labor progresses, it may be necessary to make minor adjustments to the sensor from time to time.

2. Mannheimer P, Fein M, Casciani J. Physiooptical considerations in the design of fetal pulse oximetry sensors. European Journal of Obstetrics & Gynecology and reproductive Biology. 1997;72 (suppl):S9-S19.

3. Seelbach-Göbel B, Heupel M, Kühnert M, et al. The prediction of fetal acidosis by means of intrapartum pulse oximetry. American Journal of Obstetrics and Gynecology. 1999;180:73-81.

4. Mallinckrodt Perinatal Reference Note Number 1 – The Nellcor Fetal Oxygen Saturation Monitoring System: Technical Issues. 1997.

5. James DK, Steer PJ, Weiner CP, Gonik B. High Risk Pregnancy: Management Options. W.B. Saunders Company Ltd.; 1994: 352-359.

6. Walker SC, et al. Pulse oximeter measurements of oxygen saturation in sickle cell blood. Trans. Inst. EEE, May 1988.

7. Weston-Smith SG, Acharya J, Pears TC. Pulse oximetry in sickle cell disease. Clin. Lab. Haematology. 1989;11 (3) 185-188.

8. Rackoff WR, et al. Pulse oximetry and factors associated with hemoglobin oxygen saturation in children with sickle cell disease. Blood, 1993;81 (12): 3422-3427.

9. Cunningham, FG, et al. Williams Obstetrics. 18th ed. Appleton and Lange; 1989:789.

10. Cunningham FG, et al. Williams Obstetrics. 20 th ed. Appleton and Lange; 1997:167-168, 1186.

11. Internal Mallinckrodt data.

12. Johnson N. Monitoring the fetus with a pulse oximeter. 1st International Symposium on Intrapartum Surveillance. October 18-19, 1990, Nottingham, England.

13. Dildy G, van den Berg P, Katz M, et al. Intrapartum fetal pulse oximetry: Fetal oxygen saturation trends during labor and in relation to delivery outcome. American Journal of Obstetrics and Gynecology. 1994;171:679-684.

14. Peat S, Booker M, Lanigan C, et al. Continuous intrapartum measurement of fetal oxygen saturation (letter). The Lancet. 1988:213.

15. Gardosi J, Schram C. Detection of fetal acidosis with intrapartum pulse oximetry. 19th Annual Meeting - The Society for the Study of Fetal Physiology. August 25-28, 1992, Queens Landing, Ontario, Canada, abstract G-3.

16. Seelbach-Gobel B. Reflectance pulse oximetry in fetal surveillance during labor. The 2nd World Congress of Perinatal Medicine. September 19-24, 1993, Rome, Italy, 167.

17. Seelbach-Gobel B, Butterwegge M, Kühnert M, et al. Reflectance pulse oximetry during labor. Z Geburtsh U. Perinat. 1994;198:67.

18. Sato I, Izumi A, Tamada T. Continuous fetal monitoring with pulse oximeter during labor. The 2nd World Congress of Perinatal Medicine. September 19-24, 1993, Rome, Italy, 168.

19. Buschmann J, Rall G, Knitza R. Fetal oxygen saturation measurement by transmission pulse oximetry (letter). The Lancet. 1992;339:615.

20. Siker D, Farber N, Valdelamar M, et al. Evaluation of a fetal pulse oximetry sensor during labor. Anesthesiology. 1994;81:3A, abstract A499.

21. Richardson B, Carmichael L, Homan J, et al. Electrocortical activity, electrocular activity, and breathing movements in fetal sheep with prolonged and graded hypoxemia. American Journal of Obstetrics and Gynecology. 1992;167:553-558.

22. Nijland R, Jongsma H, Oeseburg B, et al. Is there a critical value of oxygen saturation during hypoxia? 19th Annual Meeting &ndash; The Society for the Study of Fetal Physiology August 25-28, 1992, Queens Landing, Ontario, Canada, Abstract B-5.

23. Nijland R, Jongsma H, Crevels J, et al. The ductus arteriosus, pre- and post-ductal oxygen saturation measurements in fetal lambs. European Journal of Obstetrics & Gynecology and Reproductive Biology. 1994;55:135-140.

24. Kühnert M, Seelbach-Göbel B, Butterwegge M. Predictive agreement between the fetal arterial oxygen saturation and fetal scalp pH: results of the German multicenter study. American Journal of Obstetrics and Gynecology. 1998;178:330-335.

25. Goffinet F, Langer B, Carbonne B, et al. Multicenter study on the clinical value of fetal pulse oximetry. I. Methodologic evaluation. American Journal of Obstetrics and Gynecology. 1997;177:1238-1246.

26. Carbonne B, Langer B, Goffinet F, et al. Multicenter study on the clinical value of fetal pulse oximetry. II. Compared predictive values of pulse oximetry and fetal blood analysis. American Journal of Obstetrics and Gynelcology. 1997;177:593-598.

27. Dildy G, Clark S, Loucks C. Intrapartum fetal oximetry: relationship between intrapartum preductal arterial oxygen saturation and umbilical cord blood gases. American Journal of Obstetrics and Gynecology. 1993;168:340.

28. Carbonne B, Langer B, Dujardin P, et al. Predictive value of fetal pulse oximetry during labor. 14th European Congress of Perinatal Medicine. June 5-8, 1994, Helsinki, Finland, abstract 512.

29. Luttkus A. Evaluation of fetal pulse oximetry by fetal blood analysis (FBA) and its predictive value. International Journal of Gynecology & Obstetrics. September 1994; 46 (Suppl):176.

Would you like to comment on this article? This link will open your email program with the subject line completed and the url of the article you are commenting on in the body of your message.