Clinical Review

Fetal pulse oximetry: 8 vital questions

OBG Manag. 2004 March;16(3):28-44

Will this noninvasive technique improve assessment of fetal well-being? The authors analyze what the evidence to date does and does not tell.

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References

1. Dildy GA. A guest editorial: fetal pulse oximetry. Obstet Gynecol Surv. 2003;58:225-226.

2. Thacker SB, Stroup DF, Peterson HB. Efficacy and safety of intrapartum electronic fetal monitoring: an update. Obstet Gynecol. 1995;86:613-620.

3. Garite TJ, Dildy GA, McNamara H, et al. A multicenter controlled trial of fetal pulse oximetry in the intrapartum management of nonreassuring fetal heart rate patterns. Am J Obstet Gynecol. 2000;183:1049-1058.

4. Haverkamp AD, Orleans M, Langendoerfer S, et al. A controlled trial of the differential effects of continuous fetal heart rate monitoring in labor: a randomized trial. Am J Obstet Gynecol. 1979;134:399-412.

5. American College of Obstetricians and Gynecologists. Committee opinion: fetal pulse oximetry. Number 258, September 2001. Obstet Gynecol. 2001;98:523-524.

6. Zijlstra WG, Buursma A, Zwart A. Performance of an automated six-wavelength photometer (radiometer OSM3) for routine measurement of hemoglobin derivatives. Clin Chem. 1988;34:149-152.

7. Porath M, Sinah P, Dudenhausen JW, Luttkus AK. Systematic instrumental errors between oxygen saturation analysers in fetal blood during deep hypoxemia. Clin Chim Acta. 2001;307:151-157.

8. Luttkus AK, Lübke M, Büscher U, Porath M, Dudenhausen JW. Accuracy of fetal pulse oximetry. Acta Obstet Gynecol Scand. 2002;81:417-423.

9. Carter AM, Stiller R, König V, Jorgensen JS, Svendsen P, Huch R. Calibration of a reflectance pulse oximeter in fetal lambs for arterial oxygen saturations below 70%. J Soc Gynecol Invest. 1998;5:255-259.

10. McNamara H, Cung CD, Lilford R, Johnson N. Do fetal pulse oximetry readings at delivery correlate with cord blood oxygenation and acidemia? Br J Obstet Gynaecol. 1992;99:735-738.

11. Langer B, Boudier E, Haddad J, Pain L, Schlaeder G. Fetal pulse oximetry during labor of 62 patients. Fetal Diagn Ther. 1996;11:37-45.

12. Harrison AM, Lynch JM, Dean JM, Witte MK. Comparison of simultaneously obtained arterial and capillary blood gases in pediatric intensive care unit patients. Crit Care Med. 1997;25:1904-1908.

13. Nijland R, Jongsma HW, Nijhuis JG, Oeseburg B. Accuracy of fetal pulse oximetry and pitfalls in measurements. Eur J Obstet Gynecol Reprod Biol. 1997;72:S21-S27.

14. Dildy GA, van den Berg PP, Katz M, et al. Intrapartum fetal pulse oximetry: fetal oxygen saturation trends during labor and relation to delivery outcome. Am J Obstet Gynecol. 1994;171:679-684.

15. Nijland R, Jongsma H, Nijhuis J, van den Berg P, Oeseburg B. Arterial saturation in relation to metabolic acidosis in fetal lambs. Am J Obstet Gynecol. 1995;172:810-819.

16. Kühnert M, Seelbach-Göbel B, Butterwegge M. Predictive agreement between fetal arterial oxygen saturation and fetal scalp pH: results of the German multicenter study. Am J Obstet Gynecol. 1998;178:330-335.

17. Salamalekis E, Thomopoulos P, Giannaris D, et al. Computerised intrapartum diagnosis of fetal hypoxia based on heart rate monitoring and fetal pulse oximetry recordings utilizing wavelet analysis and neural networks. Br J Obstet Gynaecol. 2002;109:1137-1142.

18. Bloom SL, Swindle RG, McIntire DD, Leveno KJ. Fetal pulse oximetry: duration of desaturation and intrapartum outcome. Obstet Gynecol. 1999;93:1036-1040.

19. Seelbach-Göbel B, Heupel M, Kühnert M, et al. The prediction of fetal acidosis by means of intrapartum fetal pulse oximetry. Am J Obstet Gynecol. 1999;180:73-81.

20. Gorenberg DM, Patillo C, Hendi P, Rumney PJ, Garite TJ. Fetal pulse oximetry: correlation between oxygen desaturation, duration, and frequency and neonatal outcomes. Am J Obstet Gynecol. 2003;189:136-138.

21. Dildy GA, Thorp JA, Yeast JD, Clark SL. The relationship between oxygen saturation and pH in umbilical blood: implications for intrapartum fetal oxygen saturation monitoring. Am J Obstet Gynecol. 1996;175:682-687.

22. Leszczynska-Gorzelak B, Poniedzialek-Czajkowska E, Oleszczuk J. Fetal blood saturation during the 1st and 2nd stage of labor and its relation to the neonatal outcome. Gynecol Obstet Invest. 2002;54:159-163.

23. Alshimmiri M, Bocking AD, Gagnon R, Natale R, Richardson BS. Prediction of umbilical artery base excess by intrapartum fetal oxygen saturation monitoring. Am J Obstet Gynecol. 1997;177:775-779.

24. Rijnders RJ, Mol BW, Reuwer PJ, Drogtrop AP, Vernooij MM, Visser GH. Is the correlation between fetal oxygen saturation and blood pH sufficient for the use of fetal pulse oximetry? J Matern Fetal Neonatal Med. 2002;11:80-83.

25. Goffinet F, Langer B, Carbonne B, et al. Multicenter study on the clinical value of fetal pulse oximetry. I. Methodologic evaluation. The French Study Group on Fetal Pulse Oximetry. Am J Obstet Gynecol. 1997;177:1238-1246.

26. Schmidt S, Koslowski S, Sierra F, et al. Clinical usefulness of pulse oximetry in the fetus with non-reassuring heart rate pattern? J Perinat Med. 2000;28:298-305.

27. Vitoratos N, Salamalekis E, Saloum J, Makrakis E, Creatsas G. Abnormal fetal heart rate patterns during the active phase of labor and the value of fetal oxygen saturation. J Matern Fetal Neonatal Med. 2002;11:46-49.

28. Stiller R, von Mering R, König V, et al. How well does reflectance pulse oximetry reflect intrapartum fetal acidosis? Am J Obstet Gynecol. 2002;186:1351-1357.

29. Leszczynska-Gorzelak B, Poniedzialek-Czajkowska E, Zych I, Grzechnik M, Oleszczuk J. The usefulness of the intrapartum fetal pulse oximetry in anticipating the neonatal outcome. Ginekol Pol. 2001;72:1183-1188.

30. Nikolov A, Dimitrov A, Vakrilkova L, Iarkova N. Fetal oxygen saturation during normal delivery. Akush Ginekol. 2000;40:3-6.

31. Goldaber KG, Gilstrap LC III, Leveno K, Dax JS, McIntire DD. Pathologic fetal acidemia. Obstet Gynecol. 1991;78:1103-1107.

32. Low JA, Victory R, Derrick EJ. Predictive value of electronic fetal monitoring for intra-partum fetal asphyxia and metabolic acidosis. Obstet Gynecol. 1999;93:285-291.

33. Chua S, Yeong SM, Razvi K, Arulkumaran S. Fetal oxygen saturation during labour. Br J Obstet Gynaecol. 1997;104:1080-1083.

34. Butterwegge M. Fetal pulse oximetry and non-reassuring heart rate. Eur J Obstet Gynecol Reprod Biol. 1997;72:S63-S66.

35. Johnson N, Johnson VA, Bannister J, McNamara H. The effect of meconium on neonatal and fetal reflectance pulse oximetry. J Perinat Med. 1990;18:351-355.

36. Yam J, Chua S, Arulkumaran S. Intrapartum pulse oximetry: Part 1: Principles and technical issues. Obstet Gynecol Surv. 2000;55:163-172.

37. Carbonne B, Cudeville C, Sivan H, Cabrol D, Papiernik E. Fetal oxygen saturation measured by pulse oximetry during labor with clear and meconium-stained amniotic fluid. Eur J Obstet Gynecol Reprod Biol. 1997;72:S51-S55.

38. East CE, Colditz PB. Clinicians’ perceptions of placing a fetal oximetry sensor. J Qual Clin Pract. 2000;20:161-163.

39. Chua S, Yam J, Razvi K, Yeong SM, Arulkumaran S. Intrapartum fetal oxygen saturation monitoring in a busy labour ward. Eur J Obstet Gynecol Reprod Biol. 1999;82:185-189.

40. Luttkus AK, Friedmann W, Thomas S, Dimer JA, Dudenhausen JW. The safety of fetal pulse oximetry in parturients requiring fetal scalp blood sample. Obstet Gynecol. 1997;90:533-537.

KEY POINTS

The value of this new technology might not be so much the prediction of acidosis but identification of the well-oxygenated fetus so that labor may be safely continued in the presence of a concerning—but not ominous—fetal heart rate tracing.
The only randomized study published so far did not determine whether clinical decisions can be based solely on fetal pulse oximetry. The investigators did suggest that sensitivity and specificity for metabolic acidemia was improved in the intervention group—a promising appraisal, in contrast with previous observational data.

When a teenage nullipara underwent labor induction for preeclampsia at 37 weeks, she was given epidural analgesia and seizure prophylaxis with magnesium sulfate. Her electronic fetal heart rate (FHR) tracing was initially reassuring, with only occasional variable decelerations, but subsequently revealed a baseline of 140 beats per minute (bpm), minimal to absent variability, no accelerations, and variable decelerations to 90 bpm with rapid return to baseline.

The tracing was interpreted as nonreassuring, and a fetal pulse oximeter was inserted. It revealed a fetal oxygen saturation rate between 45% and 50%, and labor was allowed to continue. After 3.5 hours in the second stage, the patient was delivered by outlet forceps. Her infant had Apgar scores of 8 at 1 minute and 9 at 5 minutes. The umbilical arterial pH was 7.25, and base excess was–4.9.

Fetal pulse oximetry made it possible to manage this case without resorting to emergent cesarean. But is this noninvasive technology truly a step forward in intrapartum assessment of fetal well-being?

We describe what the evidence (a single randomized study and a number of observational studies) reveals about these questions:

How accurately does fetal pulse oximetry reflect the fetal condition?
What is the critical threshold for fetal oxygen desaturation?
Is a single reading reliable?
Does oximetry correlate with acid-base status?
Does the combination of oximetry and electronic monitoring improve accuracy?
Will fetal pulse oximetry improve neonatal outcomes?
How precise is it?
Is it easy to use?

Needed: Effective adjunct to electronic monitoring

Except in the chronically hypoxic fetus (which is affected by the time labor begins), the pathophysiology of acute intrapartum events is a continuum, from hypoxemia to respiratory acidosis to metabolic acidosis and, ultimately, clinical impairment. The goal of intrapartum surveillance is to detect fetal hypoxemia before it progresses to asphyxia and perinatal mortality or long-term morbidity.

Although it is approved as an adjunct to electronic fetal monitoring (EFM), fetal pulse oximetry has gained only sporadic use since it became available in the United States in 2000—even though EFM has proved disappointing as a tool for predicting fetal hypoxia. Only about 10% of US obstetrical units had fetal pulse oximetry technology as of 2002.¹

Clinicians began questioning the reliability of subjective interpretation of fetal heart tracings soon after EFM went into general use. Thirty years later, a meta-analysis of 12 randomized clinical trials involving 58,855 gravidas cast doubt on the benefits of EFM,² which is associated with an increase in operative deliveries as a result of high sensitivity but low specificity in predicting fetal hypoxia and acidosis.

FDA approval was based on sole randomized trial

The only commercially available fetal oximetry sensor, the Nellcor N-400 (Nellcor, Pleasanton, Calif), obtained US Food and Drug Administration (FDA) approval as an adjunct to EFM when the latter indicates a nonreassuring FHR pattern. That approval was based on the only randomized study³ of fetal pulse oximetry conducted, which involved 1,010 women with predefined nonreassuring FHR patterns in labor.

Goal: Reduced cesarean rate with comparable outcomes. Investigators hypothesized that adjunctive fetal oximetry would improve assessment and reduce the cesarean rate without altering neonatal outcome. Indeed, in the oximetry group, the rate of cesarean delivery performed for a nonreassuring FHR tracing (4.5% versus 10.2%; P = .007) was significantly reduced. Other findings:

Same neonatal outcomes, with no significant differences between the 2 groups.
Higher cesarean rate for dystocia in the intervention group, offsetting any advantage in the overall cesarean delivery rate (29% versus 26%). This unexpected increase in cesarean deliveries raises several possibilities:
Given the unblinded design, it is possible that clinicians, circumspect of the pulse oximetry, continued to perform cesareans for nonreassuring FHR, but labeled the indication for surgery differently. The validity of the dystocia diagnosis was discredited by a subsequent partogram analysis that showed a similar rate of arrested labor in both groups.
A nonreassuring FHR in conditions of normal fetal oxygenation is predictive of dystocia. Previous randomized studies of EFM have suggested the same thing.⁴
Dystocia is the consequence of the device itself. Anecdotal observations suggest a higher rate of persistent occiput posterior positions with fetal oximetry.