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Placental Compared With Umbilical Cord Blood to Assess Fetal Blood Gas and Acid-Base Status

From the Departments of Obstetrics and Gynaecology and Physiology, The University of Western Ontario, London, Ontario, Canada; and Department of Obstetrics and Gynecology, University California Los Angeles, Los Angeles, California.

	ABSTRACT

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OBJECTIVE: To estimate the extent to which placental cord blood sampled from the umbilical cord at its insertion into the placenta and after delivery of the placenta, is in agreement with umbilical cord blood sampled from a clamped segment of the umbilical cord after delivery of the infant, for the assessment of fetal blood gas, acid-base status, and hemoglobin levels at birth.

METHODS: Forty-eight patients were studied with arterial and venous blood sampling from the umbilical cord and from the placental cord insertion, with subsequent measurement of blood gases, pH, base excess, O₂ saturation, and hemoglobin. The relationships of corresponding measurements from the placental and umbilical vein and from the placental and umbilical artery were analyzed using regression analysis, paired analysis of grouped means, and by estimating limits of agreement.

RESULTS: The relationships between placental and umbilical cord blood measurements were described using a linear mathematical model, and although respective measurements were all significantly related (P < .01), this was strongest for both venous and arterial base excess and hemoglobin measurements (r values 0.91 to 0.99) and variably weaker for venous and arterial Po₂ (and thereby O₂ saturation measurements [r values 0.36 to 0.89]) and arterial Pco₂ (and thereby pH measurements [r values 0.66 to 0.73]). Whereas base excess and hemoglobin measurements for both the venous and arterial placental and umbilical cord bloods were close in value over the range of values studied, Po₂ and thereby O₂ saturation values were variably lower in the placental vein compared with the umbilical vein, while Pco₂ values were variably lower and thereby pH values conversely higher in the placental artery compared with the umbilical artery. Limits of agreement as a measure of the difference between paired placental and umbilical cord blood measurements were such that only those for base excess and hemoglobin were likely narrow enough to be acceptable for clinical purposes.

CONCLUSION: Placental cord blood provides for a close estimate of fetal base excess and hemoglobin status at birth, but with more error for Po₂ and thereby O₂ saturation and Pco₂ and thereby pH due to continued blood gas exchange within and across the placenta after cord clamping.

LEVEL OF EVIDENCE: III

	MATERIALS AND METHODS

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This study was approved by the University of Western Ontario Human Ethics Review Board, and procedures followed were in accordance with the ethical standards for human experimentation established by the Declaration of Helsinki of 1975, revised in 1983. Forty-eight patients were studied, term labor N = 30, term elective cesarean N = 12, and preterm labor N = 6, with characteristic data for each of the 3 patient groupings shown in Table 1. Patients studied were deemed to be low risk with the exception of the preterm labor group and were selected as a representative sampling of the general patient population with the intent of obtaining a range of cord blood values. For all patients, immediately after delivery of the infant, a segment of umbilical cord was doubly clamped and blood then sampled first from the artery and then from the vein, using 5-ml preheparinized plastic syringes. Sampling of the umbilical cord blood was always within 1 to 2 minutes of birth, with cord blood then placed on ice. After subsequent delivery of the placenta, which was variable in time from that of the infant, the umbilical cord was again sampled at its insertion into the placenta from both the artery and vein, using 5-ml preheparinized plastic syringes then placed on ice.

Approximately 1 ml of blood from the umbilical and placental arterial and venous blood samples was used for the analysis of blood gases, pH, and base excess using an ABL-500 Blood Gas Analyzer (Radiometer, Copenhagen, Denmark) and oxygen saturation and hemoglobin using an OSM2 Hemoximeter (Radiometer). This analysis was usually achieved within 45 minutes of delivery and in no case longer than 90 minutes. Additional samples of blood were obtained for later determination of Betke-Kleihauer testing and CRH levels (reported separately).

Results for the blood gases, pH and base excess, O₂ saturation, and hemoglobin are presented as regression plots, relating corresponding measurements from the placental vein to that from the umbilical vein, from the placental artery to that from the umbilical artery, and as grouped means plus or minus standard deviation. Statistical significance was determined by regression analysis and by paired t test analysis. To assess the agreement between placental and umbilical cord values, we used the method described by Bland and Altman.⁶ This method calculates the mean difference (d) between respective placental and umbilical cord measurements and the standard deviation of the differences (s). From these data, the limits of agreement (d ± 2s) can be estimated. Data analysis is presented using all patients studied, because there were no evident differences among the 3 patient groupings with the analysis. Complete data set measurements were not obtained from all patients, usually due to limited blood sampling or to technical difficulties with the blood gas analyzer or the hemoximeter (Table 2).

	RESULTS

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The amount of blood that could be sampled from the umbilical vein averaged 4.9 ± 0.3 ml (range 3.0 to 5.0 ml), whereas that from the placental vein averaged 4.7 ± 0.9 ml (range 0 to 5.0 ml). The amount of blood that could be sampled from the umbilical artery averaged 3.2 ± 1.5 ml (range 1.0 to 5.0 ml), whereas that from the placental artery averaged 3.4 ± 1.6 ml (range 0 to 5.0 ml). The time from delivery of the infant to delivery of the placenta, as an approximate measure of the interval between umbilical and placental cord blood sampling, was affected by the mode of delivery and averaged 1.5 ± 0.2 minutes (range 0 to 3.0 minutes) for the elective cesarean delivery patients compared with 5.3 ± 0.6 minutes (range 1.0 to 16.0 minutes) for the laboring patients.

The relationships between placental and umbilical cord blood measurements for Po₂, Pco₂, pH, base excess, O₂ saturation, and hemoglobin are shown in Figures 1 through 6. All of these relationships were described using a linear mathematical model with the equations generated along with the r values as shown in the figure legends. Although respective placental and umbilical cord blood measurements were all significantly related (P < .01), this was strongest for both venous and arterial base excess and hemoglobin measurements (r values 0.91 to 0.99) and variably weaker for arterial blood gas and O₂ saturation measurements (r values 0.36 to 0.76).

View larger version (26K): [in this window] [in a new window]   Fig. 1. A. The relationships between respective placental and umbilical vein and artery Po2 measurements. Relationships were described using a linear mathematical model; for vein Po2, y = 0.67x + 7.3, r = 0.80; for artery Po2, y = 0.32x + 11.4, r = 0.36. Dashed line, identity line. B. Difference between respective placental and umbilical vein and artery Po2 measurements as a function of the mean average of these measurements. The 2 solid horizontal lines indicate the lower and upper limit of agreement (d ± 2s); for vein Po2, –8.8 to 11.7 mm Hg; for artery Po2, –8.4 to 8.0 mm Hg. Open symbols, elective cesarean delivery patients; closed symbols, laboring patients; Umbil, umbilical; plac, placental. Nodwell. Fetal Cord Blood Gases and pH. Obstet Gynecol 2005.

View larger version (27K): [in this window] [in a new window]   Fig. 2. A. The relationships between respective placental and umbilical vein and artery Pco2 measurements. Relationships were described using a linear mathematical model; for vein Pco2, y = 0.92x + 4.1, r = 0.93; for artery Pco2, y = 0.69x + 9.6, r = 0.66. Dashed line, identity line. B. Difference between respective placental and umbilical vein and artery Pco2 measurements as a function of the mean average of these measurements. The 2 solid horizontal lines indicate the lower and upper limit of agreement (d ± 2s); for vein Pco2, –6.1 to 4.3 mm Hg; for artery Pco2, –5.8 to 19.9 mm Hg. Open symbols, elective cesarean delivery patients; closed symbols, laboring patients; Umbil, umbilical; plac, placental. Nodwell. Fetal Cord Blood Gases and pH. Obstet Gynecol 2005.

View larger version (24K): [in this window] [in a new window]   Fig. 3. A. The relationships between respective placental and umbilical vein and artery pH measurements. Relationships were described using a linear mathematical model; for vein pH, y = 0.96x + 0.3, r = 0.94; for artery pH, y = 0.79x + 1.5, r = 0.73. Dashed line, identity line. B. Difference between respective placental and umbilical vein and artery pH measurements as a function of the mean average of these measurements. The 2 solid horizontal lines indicate the lower and upper limit of agreement (d ± 2s); for vein pH, –0.038 to 0.051; for artery pH, –0.121 to 0.055. Open symbols, elective cesarean delivery patients; closed symbols, laboring patients; Umbil, umbilical; plac, placental. Nodwell. Fetal Cord Blood Gases and pH. Obstet Gynecol 2005.

View larger version (25K): [in this window] [in a new window]   Fig. 4. A. The relationships between respective placental and umbilical vein and artery base excess (BE) measurements. Relationships were described using a linear mathematical model; for vein base excess, y = 1.12x + 0.1, r = 0.99; for artery base excess, y = 1.01x –0.5, r = 0.91. Dashed line, identity line. B. Difference between respective placental and umbilical vein and artery base excess measurements as a function of the mean average of these measurements. The 2 solid horizontal lines indicate the lower and upper limit of agreement (d ± 2s); for vein base excess, –1.1 to 1.2 mM; for artery base excess, –1.5 to 2.4 mM. Open symbols, elective cesarean delivery patients; closed symbols, laboring patients; Umbil, umbilical; plac, placental. Nodwell. Fetal Cord Blood Gases and pH. Obstet Gynecol 2005.

View larger version (27K): [in this window] [in a new window]   Fig. 5. A. The relationships between respective placental and umbilical vein and artery O2 saturation measurements. Relationships were described using a linear mathematical model; for vein O2 saturation, y = 0.80x + 8.5, r = 0.89; for artery O2 saturation, y = 0.69x + 7.7, r = 0.76. Dashed line, identity line. B. Difference between respective placental and umbilical vein and artery O2 saturation measurements as a function of the mean average of these measurements. The 2 solid horizontal lines indicate the lower and upper limit of agreement (d ± 2s); for vein O2 saturation, –17 to 25%; for artery O2 saturation, –26 to 22%. Open symbols, elective cesarean delivery patients; closed symbols, laboring patients; Umbil, umbilical; plac, placental. Nodwell. Fetal Cord Blood Gases and pH. Obstet Gynecol 2005.

View larger version (26K): [in this window] [in a new window]   Fig. 6. A. The relationships between respective placental and umbilical vein and artery hemoglobin (Hb) measurements. Relationships were described using a linear mathematical model; for vein hemoglobin, y = 1.0x + 1.7, r = 0.96; for artery hemoglobin, y = 1.02x –6.5, r = 0.99. Dashed line, identity line. B. Difference between respective placental and umbilical vein and artery hemoglobin measurements as a function of the mean average of these measurements. The 2 solid horizontal lines indicate the lower and upper limit of agreement (d ± 2s); for vein hemoglobin, –15 to 9 g/L; for artery hemoglobin, –11 to 14 g/L. Open symbols, elective cesarean delivery patients; closed symbols, laboring patients; Umbil, umbilical; plac, placental. Nodwell. Fetal Cord Blood Gases and pH. Obstet Gynecol 2005.

For several reasons, which are well discussed by Bland and Altman,⁶ the correlation between 2 methods does not give information about the degree of error with which one can predict one measurement given the other. We therefore also assessed the agreement between respective placental and umbilical cord measurements, which are also shown in Figures 1 through 6. As can be seen, the limits of agreement (d ± 2s) as a function of the range of values studied, were generally wider for arterial than respective venous measurements, wider for Po₂, Pco₂, pH, and O₂ saturation than base excess and hemoglobin measurements, and with no evident relation between the difference and the mean for any of these measurements.

	DISCUSSION

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The umbilical artery blood gas and pH values for the term labor, term elective cesarean delivery, and preterm labor patient groups are similar to those that we (Victory R, Penava D, da Silva O, Natale R, Richardson B. Umbilical cord pH and base excess values in relation to adverse outcome events for infants delivering at term. Am J Obstet Gynecol 2004 [in press])^7,8 and others^1,2,4,9,10 have previously reported, despite the relatively small number of patients studied with the primary intent to obtain a range of values for the correlation of respective placental and umbilical cord blood measurements. The patient groups have been analyzed together because there was no evident effect of patient grouping on the outcomes of interest, although it is recognized that gestational development of the placenta and labor events could affect the cord blood changes herein noted, thereby leading to subtle differences that might be seen with larger patient numbers.

In the present study, Po₂ values from the placental vein that were obtained from the cord at its insertion into the chorionic plate after delivery of the placenta were significantly lower than those from the umbilical vein that were obtained from a clamped segment of cord after delivery of the infant. Although this difference was approximately 2 mm Hg on average, it was variably greater the higher the umbilical vein Po₂ value as indicated by the slope of the linear regression equation at 0.67, which is considerably less than 1. This in turn contributes to the modest correlation seen between respective placental and umbilical vein Po₂ values with an r value of 0.80. Although Po₂ values from the placental artery were little changed from that of the umbilical artery on average, greater increases occurred in placental values the lower the umbilical values, as indicated by the slope of the linear regression equation at 0.32. Likewise, this contributes to the weak correlation seen between respective placental and umbilical artery Po₂ values with an r value of 0.36. These changes in placental cord Po₂ values can be attributed to the cessation of umbilical blood flow after cord clamping and thus of oxygen replenishment through the umbilical venous blood, the continued use of oxygen by the placenta, and the presence of diffusional shunts within the placenta whereby umbilical venous blood exiting the area of gas exchange decreases its Po₂ by donating oxygen to the incoming umbilical arterial blood.¹¹ As such, variations in the metabolic rate of the placenta and the gradient for oxygen across the umbilical circulation at the time of cord clamping would also contribute to the modest correlation seen between respective placental and umbilical Po₂ values.

Pco₂ values from the placental vein were close to that of the umbilical vein and highly correlated over the range of values studied as indicated by the slope of the linear regression equation at 0.92 and the r value of 0.93. Conversely, Pco₂ values from the placental artery were significantly lower than that from the umbilical artery by approximately 7 mm Hg on average. This difference was variably greater the higher the umbilical artery Pco₂ value as indicated by the slope of the linear regression equation at 0.66. This again contributes to the modest correlation seen between respective placental and umbilical artery Pco₂ values with an r value of 0.68. These changes in placental arterial Pco₂ values can be attributed to the high diffusibility of carbon dioxide across the placenta and continued blood gas exchange after the cessation of umbilical blood flow with cord clamping depending on the gradient for carbon dioxide from fetal to maternal blood.¹¹ As such, the gradient from the umbilical vein blood must already be minimal and limiting for further diffusion of carbon dioxide after cord clamping, with placental and umbilical vein Pco₂ values similarly affected by maternal Pco₂ levels and the adequacy of placental gas exchange thereby accounting for the range in values seen, but with little difference in these values for any given patient.

The regression equation findings for cord pH measurements were similar to those noted for the Pco₂ measurements, with placental and umbilical vein values close to one another and placental and umbilical artery values again showing a modest correlation, indicating that observed pH changes can largely be attributed to corresponding Pco₂ changes. Not surprisingly, placental vein and artery base excess values were also close to and highly correlated with respective umbilical values because these measurements should be relatively unaffected by continued gas exchange within the placenta after cord clamping and the observed changes in Po₂ and Pco₂. However, placental artery values did show a small but nonetheless significant fall from that of the umbilical artery, in keeping with continued release of lactate by the placenta into the umbilical circulation after cord clamping^12,13 as the primary fixed acid known to contribute to reductions in base excess.² The regression equation findings for O₂ saturation measurements were intermediate between that for the Po₂ and pH measurements as determinants for this characteristic, indicating that observed O₂ saturation changes can be attributed to corresponding Po₂ and pH changes. As expected, hemoglobin measurements for the placental vein and artery were also close to and highly correlated with respective umbilical values. However, placental vein values did show a small but nonetheless significant increase from that of the umbilical vein, presumably reflecting water shifting from the placental vein compartment after cord clamping due to changes in hydrostatic pressure with uterine contraction or colloid osmotic pressure with altered transport processes.

The agreement between paired placental and umbilical cord blood measurements herein studied will depend upon biologic issues, including continued blood gas exchange across the placenta, metabolism by the placenta, and fluid shifts within the placenta as discussed, as well as the methodologic variance inherent in making these cord blood measurements. As expected given the preceding analysis, the limits of agreement for placental vein and artery Po₂ and thereby O₂ saturation measurements and placental artery Pco₂ and thereby pH measures with respective umbilical measurements were wide, thus negating their clinical usefulness as a close estimate of fetal blood gas and acid-base status at birth. Although placental vein Pco₂ and thereby pH measurements were highly correlated with respective umbilical measurements, the limits of agreement were such that placental vein measurements could be 6 mm Hg/0.04 pH units less than, to 4 mm Hg/0.05 pH units more than umbilical vein measurements. This degree of agreement or lack thereof is likely also to be unacceptable for clinical purposes. However, the limits of agreement for base excess values were narrower, such that placental vein and artery measurements could be 1.1/1.5 mM less than, to 1.2/2.4 mM more than respective umbilical measurements, which is likely to be acceptable, especially for the venous measurements. Likewise, the limits of agreement for hemoglobin values were such that placental vein and artery measurements could be 15/11 g/L less than, to 9/14 g/L more than respective umbilical measurements, which is also likely to be acceptable for clinical purposes. As such, blood obtained from the cord at its insertion into the chorionic plate after delivery of the placenta can provide an alternative source to that obtained from a clamped section of the cord after delivery of the infant, with a close estimate for base excess and hemoglobin values at birth, but with more error for the other cord blood measurements.

It should be noted that the limits of agreement for the cord blood measurements as presented apply specifically to the patients and range of cord blood values herein studied and are only estimates of the limits of agreement that apply for the general population. However, given the range of cord blood values studied and the lack of any obvious effect on placental–umbilical cord blood differences, as well as the supporting biologic mechanisms for the findings as outlined, it is likely that the limits of agreement as presented are also reasonable estimates for the larger patient population.

	Footnotes

 
The authors thank Ms. M. Sinacori and Mr. B. Matushewski for technical assistance.

Reprints are not available. Address correspondence to: Bryan S. Richardson, MD, Department of Obstetrics & Gynaecology, St. Joseph's Health Care London, 268 Grosvenor Street, Room B325, London, Ontario, Canada N6A 4V2; e-mail: brichar1{at}uwo.ca.

Received June 14, 2004. Received in revised form August 23, 2004. Accepted September 1, 2004.

doi:10.1097/01.AOG.0000146635.51033.9d

	REFERENCES

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
1. Gordon A, Johnson JWC. Value of umbilical blood acid-base studies in fetal assessment. J Reprod Med 1985;30:329–35.[Medline]

2. Low JA. The role of blood gas and acid-base assessment in the diagnosis of intrapartum fetal asphyxia. Am J Obstet Gynecol 1988;159:1235–40.[Medline]

3. American College of Obstetricians and Gynecologists. Utility of umbilical cord blood acid-base assessment. ACOG Committee Opinion Number 138. Washington, DC: ACOG; 1994.

4. American College of Obstetricians and Gynecologists. Umbilical artery blood acid-base analysis. ACOG Technical Bulletin Number 216. Washington, DC: ACOG; 1995.

5. Ross MG, Gala R. Use of umbilical artery base excess: algorithm for the timing of hypoxic injury. Am J Obstet Gynecol 2002;187:1–9.[Medline]

6. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;1:307–10.[Medline]

7. Richardson B, Nodwell A, Webster K, Alshimmiri M, Gagnon R, Natale R. Fetal oxygen saturation and fractional extraction at birth and the relationship to measures of acidosis. Am J Obstet Gynecol 1998;178:572–9.[Medline]

8. Victory R, Penava D, da Silva O, Natale R, Richardson B. Umbilical cord pH and base excess values in relation to neonatal morbidity for infants delivered preterm [published erratum appears in Am J Obstet Gynecol 2004;190:546]. Am J Obstet Gynecol 2003;189:803–7.

9. Dickinson JE, Eriksen NL, Meyer BA, Parisi VM. Effect of preterm birth on umbilical cord blood gases. Obstet Gynecol 1992;79:575–8.[Abstract/Free Full Text]

10. Thorp JA, Dildy GA, Yeomans ER, Meyer BA, Parisi VM. Umbilical cord blood gas analysis at delivery. Am J Obstet Gynecol 1996;175:517–22.[Medline]

11. Meschia G. Placental respiratory gas exchange and fetal oxygenation. In: Creasy RK, Resnik R, editors. Maternal-fetal medicine principles and practice. Philadelphia (PA): Saunders; 2004. p. 199–207.

12. Char VC, Creasy RK. Lactate and pyruvate as fetal metabolic substrates. Pediatr Res 1976;10:231–4.[Medline]

13. Battaglia FC. Placental transfer in relation to fetal demand. Placenta 1981;2(suppl):3–9.

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Nodwell, A. Articles by Richardson, B. Search for Related Content PubMed PubMed Citation Articles by Nodwell, A. Articles by Richardson, B. Related Collections Basic Science Labor and operative obstetrics Maternal/fetal physiology Placenta