EUROPEAN ASSOCIATION OF PERINATAL MEDICINE (EAPM) Position statement: Use of appropriate terminology for situations related to inadequate fetal oxygenation in labor

In high-resource countries, adverse perinatal outcomes are currently rare in term, non-malformed fetuses, undergoing labor, but they remain a leading cause of medico-legal dispute. Precise terminology is important to describe situations related to inadequate fetal oxygenation in labor, to ensure appropriate communication between healthcare professionals and adequate transmission of information to parents. This position statement provides consensus definitions from European perinatologists and midwives regarding the most appropriate terminology to describe situations related to inadequate fetal oxygenation in labor: suspected fetal hypoxia, severe newborn acidemia, newborn metabolic acidosis, and hypoxic-ischemic encephalopathy. It also identifies terms that are imprecise or nonspecific to this situation, and should therefore be avoided by healthcare professionals: fetal well-being, fetal stress, fetal distress, non-reassuring fetal state, and birth asphyxia.

How well are we collecting umbilical cord lactate and gas samples?

AIMS

The aim of this study is to measure staff compliance with the local umbilical cord lactate (UCL) sampling guideline and investigate the quality of paired UCG samples at a tertiary maternity unit.

METHODS

We performed a retrospective consecutive sampling of 100 babies delivered via emergency caesarean section and 50 babies with each of all other guideline-based indications for UCL sampling born on and before 31 December 2021. Data were extracted from physical and electronic records. Compliance with guideline-based indications for UCL at birth was measured. The proportion of valid UCG samples was calculated. Samples were considered invalid under the following cases: (i) inadvertently collecting from the same vessel, (ii) switching arterial and venous samples, (iii) collecting from only one vessel or (iv) committing errors during sample collection and handling.

RESULTS

Of the samples collected at birth from 321 babies, 280 (87%) had UCL. Small for gestational age and concerns about fetal well-being in labour were indications associated with poorer compliance, 66% and 78%, respectively. About 99 (44%) babies of 226 babies with UCG performed had valid UCG samples. The most common reasons for invalid samples were collection and handling errors (22%) and inadvertent collection from the same vessel (15%).

CONCLUSIONS

Generally, compliance with the guidelines is good. However, invalid UCG samples were more frequent than expected.

Umbilical Cord Blood Gas Pairs with Near-Identical Results: Probability of Arterial or Venous Source

OBJECTIVE

 In studies of concomitant arterial-venous umbilical cord blood gases (CAV-UBGs), approximately 10% of technically valid samples have very similar pH and/or pCO2 values and were probably drawn from the same type of blood vessel. Without a way to objectively determine the source in these cases, it has been argued that most of these same-source CAV-UBGs are venous because the vein is larger and more easily sampled than the artery. This study aimed to calculate the probability of an arterial (ProbAS) or venous source (ProbVS) of same-source CAV-UBGs in the clinically and medicolegally important pH range of 6.70 to 7.25 using a statistical predictive model based on the cord blood gas values.

STUDY DESIGN

 Starting with a dataset of 56,703 CAV-UBGs, the ProbAS, ProbVS, and respective 95% confidence intervals (CIs) were calculated for the 241 sample pairs with near-identical pH, pCO2, and pO2 values and a pH of 6.70 to 7.25. Using a previously validated generalized additive model, the source was categorized as: Probable Arterial or Highly Probable Arterial if the ProbAS and CIs were >0.5 or >0.8, respectively; Probable Venous or Highly Probable Venous if the ProbVS and CIs were >0.5 or >0.8, respectively; or Indeterminant if the CIs encompassed ProbAS/VS = 0.5.

RESULTS

 A total of 39% of the same-source CAV-UBGs were Probable Arterial, 56% were Probable Venous, and 5% were Indeterminant. However, considering samples with a pH ≤7.19, 80% were Probable Arterial and 16% were Probable Venous. Considering the Highly Probable categories, the more acidemic specimens were 9 times more likely to be arterial than venous. Similarly, CAV-UBGs with pCO2 > 8.2 kPa (62 mm Hg) or pO2 ≤ 1.9 kPa (14 mm Hg) were more likely to be in the arterial rather than the venous categories.

CONCLUSION

 Same-source CAV-UBGs in the more acidemic, hypercarbic, or hypoxemic ranges are more likely to be arterial than venous.

KEY POINTS

· Umbilical cord arterial/venous gases (CAV-UBGs) with similar values are thought to be mainly venous.. · A validated statistical model was used to predict the probability an arterial or venous source.. · CAV-UBGs with very similar values and pH >  7.19 are likely venous; however, those with pH ≤ 7.19 and/or pCO2 >  8.2 kPa and/or pO2 ≤1.9 kPa are more likely arterial..

Umbilical cord pH, blood gases, and lactate at birth: normal values, interpretation, and clinical utility

Normal birth is a eustress reaction, a beneficial hedonic stress with extremely high catecholamines that protects us from intrauterine hypoxia and assists in the rapid shift to extrauterine life. Occasionally the cellular O₂ requirement becomes critical and an O₂ deficit in blood (hypoxemia) may evolve to a tissue deficit (hypoxia) and finally a risk of organ damage (asphyxia). An increase in H⁺ concentration is reflected in a decrease in pH, which together with increased base deficit is a proxy for the level of fetal O₂ deficit. Base deficit (or its negative value, base excess) was introduced to reflect the metabolic component of a low pH and to distinguish from the respiratory cause of a low pH, which is a high CO₂ concentration. Base deficit is a theoretical estimate and not a measured parameter, calculated by the blood gas analyzer from values of pH, the partial pressure of CO₂, and hemoglobin. Different brands of analyzers use different calculation equations, and base deficit values can thus differ by multiples. This could influence the diagnosis of metabolic acidosis, which is commonly defined as a pH <7.00 combined with a base deficit ≥12.0 mmol/L in umbilical cord arterial blood. Base deficit can be calculated as base deficit in blood (or actual base deficit) or base deficit in extracellular fluid (or standard base deficit). The extracellular fluid compartment represents the blood volume diluted with the interstitial fluid. Base deficit in extracellular fluid is advocated for fetal blood because a high partial pressure of CO₂ (hypercapnia) is common in newborns without concomitant hypoxia, and hypercapnia has a strong influence on the pH value, then termed respiratory acidosis. An increase in partial pressure of CO₂ causes less increase in base deficit in extracellular fluid than in base deficit in blood, thus base deficit in extracellular fluid better represents the metabolic component of acidosis. The different types of base deficit for defining metabolic acidosis in cord blood have unfortunately not been noticed by many obstetrical experts and organizations. In addition to an increase in H⁺ concentration, the lactate production is accelerated during hypoxia and anaerobic metabolism. There is no global consensus on definitions of normal cord blood gases and lactate, and different cutoff values for abnormality are used. At a pH <7.20, 7% to 9% of newborns are deemed academic; at <7.10, 1% to 3%; and at <7.00, 0.26% to 1.3%. From numerous studies of different eras and sizes, it can firmly be concluded that in the cord artery, the statistically defined lower pH limit (mean -2 standard deviations) is 7.10. Given that the pH for optimal enzyme activity differs between different cell types and organs, it seems difficult to establish a general biologically critical pH limit. The blood gases and lactate in cord blood change with the progression of pregnancy toward a mixed metabolic and respiratory acidemia because of increased metabolism and CO₂ production in the growing fetus. Gestational age-adjusted normal reference values have accordingly been published for pH and lactate, and they associate with Apgar score slightly better than stationary cutoffs, but they are not widely used in clinical practice. On the basis of good-quality data, it is reasonable to set a cord artery lactate cutoff (mean +2 standard deviations) at 10 mmol/L at 39 to 40 weeks' gestation. For base deficit, it is not possible to establish statistically defined reference values because base deficit is calculated with different equations, and there is no consensus on which to use. Arterial cord blood represents the fetus better than venous blood, and samples from both vessels are needed to validate the arterial origin. A venoarterial pH gradient of <0.02 is commonly used to differentiate arterial from venous samples. Reference values for pH in cord venous blood have been determined, but venous blood comes from the placenta after clearance of a surplus of arterial CO₂, and base deficit in venous blood then overestimates the metabolic component of fetal acidosis. The ambition to increase neonatal hemoglobin and iron depots by delaying cord clamping after birth results in falsely acidic blood gas and lactate values if the blood sampling is also delayed. Within seconds after birth, sour metabolites accumulated in peripheral tissues and organs will flood into the central circulation and further to the cord arteries when the newborn starts to breathe, move, and cry. This influence of "hidden acidosis" can be avoided by needle puncture of unclamped cord vessels and blood collection immediately after birth. Because of a continuing anaerobic glycolysis in the collected blood, it should be analyzed within 5 minutes to not result in a falsely high lactate value. If the syringe is placed in ice slurry, the time limit is 20 minutes. For pH, it is reasonable to wait no longer than 15 minutes if not in ice. Routine analyses of cord blood gases enable perinatal audits to gain the wisdom of hindsight, to maintain quality assurance at a maternity unit over years by following the rate of neonatal acidosis, to compare results between hospitals on regional or national bases, and to obtain an objective outcome measure in clinical research. Given that the intrapartum cardiotocogram is an uncertain proxy for fetal hypoxia, and there is no strong correlation between pathologic cardiotocograms and fetal acidosis, a cord artery pH may help rather than hurt a staff person subjected to a malpractice suit based on undesirable cardiotocogram patterns. Contrary to common beliefs and assumptions, up to 90% of cases of cerebral palsy do not originate from intrapartum events. Future research will elucidate whether cell injury markers with point-of-care analysis will become valuable in improving the dating of perinatal injuries and differentiating hypoxic from nonhypoxic injuries.

Umbilical cord blood gases: probability of arterial or venous source in acidemia

OBJECTIVES

Umbilical cord blood gases (UBG) may be a critical element in the assessment of a depressed newborn infant but in some cases the arterial or venous UBG source is uncertain making clinical and/or medical-legal interpretation difficult. Objective: to estimate the probability of an arterial (ProbAS) or venous (ProbVS) UBG source depending on blood gas parameters in acidemic cases.

METHODS

A total of 56,703 pairs of concomitant arterial and venous (CAV) UBG results assayed over an 8.8-year period were analyzed. Specimen pairs with preanalytical issues, duplicate source, or physiologically out-of-range or uninterpretable results were excluded. The 3,579 CAV-UBGs with an arterial and venous pH 6.70 to 7.25 were analyzed. Generalized additive model (gam)-based binomial logistic regressions were used to determine the ProbAS and ProbVS according to the blood gas parameters.

RESULTS

The relative differences between arterial and venous medians were: pO₂ ‒47%, pCO₂ 22%, pH -11%, and BD 4%. Below a median of 2.4 kPa, the lower the pO₂, the higher the ProbAS. Above this value, the higher the pO₂, the lower the ProbAS. An Excel worksheet is provided to calculate ProbAS and ProbVS from the regression model for different combinations of pH, pCO₂, and pO₂ values. Considering ProbAS and ProbVS above a cutoff 0.8, the model correctly identified the source in 56% of cases while 41% were indeterminant and 3% were erroneous.

CONCLUSIONS

The probability of an arterial or venous source of an umbilical blood gas can be estimated based on the pH, pCO₂, and pO₂ in most acidemic specimens.

Predelivery placenta-associated biomarkers and computerized intrapartum fetal heart rate patterns

Background

Increasing syncytiotrophoblast stress in term and postdate placentas is reflected by increasing antiangiogenic dysregulation in the maternal circulation, with low "proangiogenic" placental growth factor concentrations and increased "antiangiogenic" soluble fms-like tyrosine kinase-1 concentrations. Imbalances in these placenta-associated proteins are associated with intrapartum fetal compromise and adverse pregnancy and delivery outcome. Cardiotocography is widely used to assess fetal well-being during labor, but it is insufficient on its own for predicting adverse neonatal outcome. Development of improved surveillance tools to detect intrapartum fetal stress are needed to prevent neonatal adverse outcome.

Objective

This study aimed to assess whether predelivery circulating maternal angiogenic protein concentrations are associated with intrapartum computerized fetal heart rate patterns, as calculated by the Oxford System for computerized intrapartum monitoring (OxSys) 1.7 prototype. We hypothesized that in pregnancies with low "proangiogenic" placental growth factor levels, increased "antiangiogenic" soluble fms-like tyrosine kinase-1 levels, and increased soluble fms-like tyrosine kinase-1-placental growth factor ratio, the OxSys 1.7 prototype will generate more automated alerts, indicating fetal compromise. Our secondary objective was to investigate the relationship between maternal circulating placenta-associated biomarkers and rates of automated alerts in pregnancies with and without adverse neonatal outcome.

Study Design

This was an observational prospective cohort study conducted at a single tertiary center from September 2016 to March 2020. Of 1107 singleton pregnancies (gestational week ≥37⁺⁰), 956 had available prelabor and predelivery placental growth factor and soluble fms-like tyrosine kinase-1 concentrations and intrapartum cardiotocography recordings. All neonatal and delivery outcomes were externally reviewed and categorized into 2 groups-the "complicated" group (n=32) and the "uncomplicated" group (n=924)-according to predefined adverse neonatal outcome. Eight different cardiotocography features were calculated by OxSys 1.7: baseline at start of cardiotocography, baseline at end of cardiotocography, short-term variation at start, short-term variation at end, nonreactive initial trace, and throughout the entire cardiotocography, maximum decelerative capacity, total number of prolonged decelerations, and OxSys 1.7 alert. OxSys 1.7 triggered an alert if the initial trace was nonreactive or if decelerative capacity and/or the number of prolonged decelerations exceeded a predefined threshold. Included women and attending clinicians were blinded to both biomarker and OxSys 1.7 results.

Results

Mean maternal placental growth factor concentration was lower in the group with OxSys 1.7 alert compared with the group without the alert (151 vs 169 pg/mL; P=.04). There was a weak negative correlation between predelivery high soluble fms-like tyrosine kinase-1 and low short-term variation start (r _s=-0.068; 95% confidence interval, -0.131 to -0.004; P=.036), predelivery high soluble fms-like tyrosine kinase-1 and low short-term variation end (r _s=-0.068; 95% confidence interval, -0.131 to -0.005; P=.036), and high soluble fms-like tyrosine kinase-1-placental growth factor ratio and low short-term variation end (r _s=-0.071; 95% confidence interval, -0.134 to -0.008; P=.027). The rate of decelerative capacity alerts increased more rapidly as placental growth factor decreased in the "complicated" compared with the "uncomplicated" group (0% to 17% vs 4% to 8%).

Conclusion

More automated alerts indicative of fetal distress were generated by OxSys 1.7 in pregnancies with low maternal predelivery placental growth factor level, in line with likely increasing placental stress toward the end of the pregnancy. An antiangiogenic predelivery profile (lower placental growth factor) increased the rates of alerts more rapidly in pregnancies with adverse neonatal outcome compared with those without. We suggest that future studies developing and testing prediction tools for intrapartum fetal compromise include predelivery maternal placental growth factor measurements.

Improvement of Umbilical Cord Blood Gas Analysis with Implementation of Clot Catchers

Background

Umbilical cord blood gas testing is a key component of objective pre- and perinatal evaluation of fetal acid base status to determine presence of intrapartum asphyxia and risk of neonatal encephalopathy. Heparinized cord blood is more likely to form small clots than other blood sources, which can interfere with, or preclude, sample analysis. Cord blood samples are irreplaceable and cannot be recollected, thereby compromising clinical decision-making when analysis is not possible. We evaluated processes to prevent excessive rates of cord blood clotting and quantified their impact on successful testing of blood gas specimens.

Methods

Verified result and cancellation data were obtained retrospectively from the laboratory information system. Clot catchers were evaluated using noncord remnant specimens. Collection syringes were compared via collection from remnant cord sections.

Results

Prior to implementation of any interventions, retrospective analysis indicated a cancellation rate of 18.6% for umbilical cord blood gas specimens (arterial and venous) and 0.7% for noncord blood arterial and venous samples. Clot catchers were validated for clinical use, with a bias of &lt;±4% for all analytes. After clot catchers were implemented for all cord specimens, cancellation rate decreased approximately 5-fold in the first month and remained &lt;5% a year after implementation. A limited comparison of two heparin syringe types revealed a small difference in the overall rate of specimen clotting.

Conclusions

Implementation of clot catchers was acceptable for analysis of cord blood samples, and when implemented resulted in a sustained 5-fold decrease in the rate of cord blood gas order cancellation.

Association of umbilical cord blood gas values with mortality and severe neurologic injury in preterm neonates <29 weeks' gestation: a national cohort study

BACKGROUND

Umbilical cord arterial and venous blood gas values reflect the acid-base balance status of a newborn at birth. Derangement in these values has been linked to poor neonatal outcomes in term and late preterm neonates; however, the utility of these values in preterm neonates of <29 weeks' gestation is unclear.

OBJECTIVE

This study aimed to determine the associations of umbilical cord arterial and venous blood gas values with neonatal mortality and severe neurologic injury in extremely preterm neonates and to identify the cutoff values associated with 2.5-fold increases or decreases in the posttest probabilities of outcomes.

STUDY DESIGN

This was a retrospective cohort study of neonates who were born at 23+0 to 28+6 weeks' gestation between January 1, 2018 and December 31, 2019, and who were admitted to neonatal units in Canada.

EXPOSURE

Various cut-offs of umbilical cord blood gas values and lactate values were studied.

MAIN OUTCOMES AND MEASURES

The main outcomes were mortality before discharge from the neonatal unit and severe neurologic injury defined as grade 3 or 4 periventricular or intraventricular hemorrhage or periventricular leukomalacia. The outcome rates were calculated for various cutoff values of umbilical cord blood gas parameters and were adjusted for birthweight, gestational age, sex, and multiple births. Likelihood ratios were calculated to derive posttest probabilities.

RESULTS

A total of 1040 and 1217 neonates had analyzable umbilical cord arterial and venous blood gas values, respectively. In the cohort, the mean (standard deviation) gestational age was 26.5 (1.5) weeks, the mean birthweight was 936 (215) g, the prevalence of mortality was 10% (105/1040), and the prevalence of severe neurologic injury was 9% (92/1016). An umbilical cord arterial pH of ≤7.1 and base excess of ≤-12 mmol/L were associated with >2.5-fold higher posttest probability of mortality, and an umbilical cord arterial or venous lactate value of <3 was associated with a 2.5-fold lower posttest probability of mortality. An umbilical cord arterial base excess of <-16 mmol/L was associated with a higher posttest probability of severe neurologic injury, whereas a lactate value of <3 was associated with a lower posttest probability.

CONCLUSION

In preterm neonates of <29 weeks' gestation, low umbilical cord arterial pH and high umbilical cord arterial base excess values were associated with a clinically important increase in the posttest probability of mortality, whereas low umbilical cord arterial or venous lactate values were associated with a decrease in the posttest probability of mortality.

Guided training has a beneficial effect on umbilical cord blood sampling quality

OBJECTIVE

Umbilical cord arterial blood gas analysis is important for neonatal assessment at birth, particularly for determining asphyxia. In April 2019, our labor ward faculty held systemic teaching sessions for midwives, aimed to describe and to exercise proper sampling from both the umbilical cord artery and vein, to ensure biological validity of the values obtained. Our aim was to estimate the rates of inadequate umbilical blood sampling and to evaluate the effect of guided training on the quality of sampling.

STUDY DESIGN

This retrospective interventional cohort study included all the women admitted to the delivery room, with a record of postpartum umbilical cord blood sampling. Umbilical cord sampling was considered adequate if two measurements were recorded with a veno-arterial pH gradient of at least 0.02 and an arterio-venous pCO₂ gradient of no less than 0.5 kPa. Rates of inadequate sampling were compared between women who gave birth in the year preceding and the year following the guidance. Clinical characteristics were compared between the groups of adequate and inadequate sampling.

RESULTS

Overall, 3,779 women gave birth in the year preceding guidance, and 3,649 in the subsequent year. Of these, 1,112 (29.4%) and 1,105 (30.2%), respectively, underwent umbilical sampling. In the year following the guidance, 750 (67.8%) adequate samples were drawn compared to 692 (62.2%) prior the guidance. This difference demonstrated significant improvement (OR 1.28, 95% CI 1.07-1.52, P = 0.006) in umbilical vessel sampling. Following multivariate logistic regression, inadequate sampling was associated with newborn weight below 2500 g (aOR 1.6, 95% CI 1.2-2.1, p = 0.001), spontaneous vaginal delivery with a possible fetal metabolic abnormality (aOR 2.2, 95% CI 1.7-2.7, p < 0.001), and vacuum deliveries (aOR 1.9, 95% CI 1.5-2.5, p < 0.001).

CONCLUSIONS

Guided training of proper umbilical blood sampling may reduce the rate of inadequate postpartum blood gas results. Labor wards should consider carrying out annual demonstrations of proper umbilical blood collection, with emphasis on factors that affect the quality of the samplings.

The association between placenta-associated circulating biomarkers and composite adverse delivery outcome of a likely placental cause in healthy post-date pregnancies

INTRODUCTION

Post-date pregnancies have an increased risk of adverse delivery outcome. Our aim was to explore the association between placenta-associated circulating biomarkers and composite adverse delivery outcome of a likely placental cause in clinically healthy post-date pregnancies.

MATERIAL AND METHODS

Women with healthy singleton post-date pregnancies between 40⁺² and 42⁺²  weeks of gestation were recruited to this prospective, observational study conducted at Oslo University Hospital, Norway (NCT03100084). Placental growth factor (PlGF) and soluble fms-like tyrosine kinase-1 (sFlt-1) were measured in the maternal serum samples closest to delivery. The composite adverse delivery outcome included fetal acidemia, low Apgar score (<4 at 1 min or <7 at 5 min), asphyxia, fetal death, assisted ventilation for more than 6 h, meconium aspiration, hypoxic-ischemic encephalopathy, therapeutic hypothermia, operative delivery due to fetal distress, or pathological placental histology findings. Two study-independent senior consultant obstetricians blinded to biomarker results concluded, based on clinical expert opinion, whether the adverse delivery outcomes were most likely associated with placental dysfunction ("likely placental cause") or not. Means were compared using one-way analysis of variance and Bonferroni corrected pairwise comparisons between groups. Receiver operating characteristic (ROC) curves assessed the predictive ability of PlGF, sFlt-1/PlGF ratio, and PlGF <10th centile after adjustment for gestational age at blood sampling.

RESULTS

Of 501 pregnancies reviewed for predefined adverse delivery outcomes and for a likely placental cause, 468 were healthy pregnancies and subsequently assigned to either the "uncomplicated" (no adverse outcome, n = 359), "intermediate" (non-placental cause/undetermined, n = 90), or "complicated" (likely placental cause, n = 19) group. There was a significant difference in mean PlGF and sFlt-1/PlGF ratio between the "complicated", "intermediate", and "uncomplicated" groups (108, 185, and 179 pg/mL, p = 0.001; and 48.3, 23.4, and 24.6, p = 0.002, respectively). There was a higher proportion of PlGF concentration <10th centile in the "complicated" group compared with the "intermediate" and "uncomplicated" groups (42.1% vs. 11.1% and 9.5%, p = 0.001). The largest area under the ROC curve for predicting "complicated" outcome was achieved by PlGF concentration and gestational age at blood sampling (0.76; 95% CI 0.65-0.86).

CONCLUSIONS

In clinically healthy post-date pregnancies, an antiangiogenic pre-delivery profile (lower PlGF level and higher sFlt-1/PlGF ratio) was associated with composite adverse delivery outcome of a likely placental cause.

Umbilical artery carbon dioxide decreases the risk for hypoxic-ischaemic encephalopathy

AIM

An accurate biomarker for metabolic acidosis at birth is needed. Our aims were to investigate the link between umbilical artery pCO₂ and the risk for hypoxic-ischaemic encephalopathy (HIE) and to compare false-negative screen results in newborn infants with HIE using three umbilical artery blood gas biomarkers.

METHODS

From a cohort of newborn infants ≥35 weeks born in Ottawa, Canada, between January 2007 and December 2016, we highlighted those with HIE or who died. We compared the umbilical artery pCO₂ for matched pH >mean versus matched pH ≤mean. We compared false-negative rates for three umbilical artery biomarkers-pH <7.0, base deficit ≥16 mmol/L and neonatal eucapnic pH ≤7.14.

RESULTS

This study included 51 286 newborn infants, 51% male and a mean gestational age of 38.9 ± 1.5 weeks. The rate for HIE or death with umbilical artery pCO₂ for matched pH >mean was 22%, compared to 78% for matched pH ≤mean. In 60 HIE or deaths, the false-negative rate for umbilical artery neonatal eucapnic pH ≤7.14 was 8%; compared to 31% for pH <7.00 and 36% for base deficit ≥16 mmol/L.

CONCLUSION

The rate of HIE or death is lower in newborn infants with higher pCO₂ . Using neonatal eucapnic pH decreases the risk of missing newborn infants with HIE.

Gestational age reference ranges for umbilical cord blood lactate: An external validation study of post-date pregnancies

A previous study published in 2008 by Wiberg et al demonstrated increasing umbilical cord blood lactate at delivery by gestational age in vigorous offspring (n = 10 169, gestational age 24-43 weeks). Based on these results the authors concluded that gestational age-independent umbilical cord lactate cut-off could give false-negative or false-positive diagnosis of lacticemia. To our knowledge, these findings have not been incorporated into clinical interpretations in delivery units. To perform an external validity study for the findings by Wiberg et al, we analyzed umbilical cord blood lactate levels according to gestational age in a post-date delivery study population at our large, tertiary obstetric unit. The parallel finding of our study to that of Wiberg et al highlights the importance of using available gestational age dependent reference ranges (eg as presented in Wiberg's publication), when interpreting umbilical cord blood lactate levels for fetal wellbeing.

Comparisons between umbilical cord biomarkers for newborn hypoxic-ischemic encephalopathy

Background: Cord blood umbilical artery (Ua) pH, base deficit (BD), and pH eucapnic Blickstein/Green-50 may mislead clinicians to identify newborns at risk for hypoxic-ischemic encephalopathy. Neonatal eucapnic pH (pH euc-n Racinet-54) may be a comprehensive alternative. The goal of the study is to compare the predictive performance of these four biomarkers for the combined primary outcome of hypoxic-ischemic encephalopathy/death.Methods: This retrospective cohort study includes newborns ≥35 weeks gestational age. Receiver operating characteristics curves analysis was performed for Ua cord pH, BD, pH euc-n Racinet-54, and pH eucapnic Blickstein/Green-50 for the global cohort and for two subgroups of newborns with Ua cord pH ≤ 7.15. Cutoff values were derived for all four markers.Results: From the original cohort of 61,037 newborns born between 1 January 2007 and 31 December 2016, we excluded cases with major congenital malformations and missing/incomplete data. The global cohort includes 51,286 newborns and 60 newborns afflicted with hypoxic-ischemic encephalopathy (HIE)/death. The area under the curves (AUC) derived from the global cohort were comparable between Ua cord pH (0.95; 95%CI = 0.94-0.95), BD (0.93; 95%CI = 0.93-0.93), pH euc-n Racinet-54 (0.93; 95% CI = 0.93-0.93), and lower for pH Blickstein/Green-50 (0.78; 95% CI = 0.77-0.78) (p < .05). Within newborn with severe acidemia (pH ≤ 7.00) and moderate acidemia (7.00 ≤ pH ≤ 7.15), pH euc-n Racinet-54 had the largest AUC and best positive likelihood ratios especially for sensitivity ≥ 0.80 to minimize false negative cases.Conclusion: In this large retrospective study, predictive performance for Ua cord pH, BD, and pH euc-n Racinet-54 are comparable when applied to the global group. For newborns with Ua cord pH ≤ 7.00 and Ua cord 7.00 ≤ pH ≤ 7.15, pH euc-n Racinet-54 appears better to identify those with HIE/death, especially when the target is sensitivity > 80%. Prospective studies will confirm if pH euc-n Racinet-54 is a better alternative to Ua cord pH and BD to evaluate newborn acid-base physiology.

Neonatal cord blood eucapnic pH: A potential biomarker predicting the need for transfer to the NICU

INTRODUCTION

The best biomarker for neonatal metabolic acidosis (NMA) and its related complications is still a matter of debate. Umbilical artery (Ua) cord pH is not sufficiently specific, as is lactatemia, while base deficit is considered to offer no added value. From a physiological point of view, the calculated neonatal eucapnic pH is a more specific marker for neonatal metabolic acidosis and may be a better predictor of birth complications of hypoxic origin, because complications related to asphyxia are always preceded by neonatal depression leading to a transfer to a neonatal intensive care unit (NICU) for close monitoring.

OBJECTIVE

This study aimed to test the hypothesis that in a group of neonates with significant acidemia, neonatal eucapnic pH (pH euc-n) predicts NICU admission better than the Ua cord pH does.

METHODS

From a cohort of 5,392 infants all born at ≥35 weeks' gestation, we identified a group of 30 cases with Ua cord pH <7.0. We calculated the area under the curve (AUC) for pH euc-n and Ua cord pH using the receiver-operating characteristic (ROC) curve and compared the performance of these biological markers in predicting transfer to the NICU. Cut-off points were determined by selecting the best value of the positive likelihood ratio that maximizes the accuracy of prediction.

RESULTS

From the 30 newborns diagnosed with significant acidemia, four infants were transferred to the NICU. No case of neonatal encephalopathy was observed. In these infants, the pH euc-n AUC (0.66) was significantly higher than the Ua cord pH AUC (0.44) (P<0.005), with the best pH euc-n cut-off value at 7.11.

CONCLUSION

Despite the study limitations, our results suggest that pH euc-n is a better marker than Ua pH for predicting admission to the NICU in newborns with acidemia at birth. These are preliminary results and further investigations are mandatory in larger population samples to confirm these findings and to determine the optimal cut-off value for pH euc-n for the most accurate prediction of a complicated transition to extrauterine life and, potentially, neonatal hypoxic-ischemic encephalopathy.

Reference percentiles for paired arterial and venous umbilical cord blood gases: An indirect nonparametric approach

BACKGROUND

Reference intervals for arterial and venous umbilical cord blood gas (UCBG) parameters are scarce, are mainly focused on pH, pO2, pCO2 and base deficit, and are usually assessed using parametric tests, despite a generally skewed data distribution. Here, the purpose is to determine reference percentiles for nine parameters of concomitant arterial and venous UCBG (CAV-UCBG) from neonates at birth, using nonparametric tests.

METHODS

Results of CAV-UCBG, assayed over a 4.5-year period, were extracted from a hospital laboratory database for pH, pCO2, pO2, oxygen saturation, concentration of total oxygen, total carbon dioxide, hydrogen carbonate, total haemoglobin, and acid-base excess. Exclusion criteria were: a venous-arterial pH difference <0.02, an arterial-venous pCO2 <0.7 kPa, and a venous pCO2 <2.9 kPa. Nonparametric bivariate kernel density estimations were used for the selection of plots within the 95% percentile surface of the pCO2-to-pH relationship (NBKDE-95P). Outliers from skewed data were removed using an adjusted-Tukey method, and percentiles were calculated according to the CLSI EP28-A3 nonparametric method.

RESULTS

Overall, 31% (5033/16164) of CAV-UCBG were discarded using the three exclusion criteria. Then, 6% (670/11131) of CAV-UCBG were excluded from the NBKDE-95P, and 0.1 to 3.5% outliers were subsequently removed. Depending on the parameter, the 2.5th and 97.5th percentiles from the whole group were similar or slightly narrower compared to reference intervals from other studies, while those from female and male neonates did not differ substantially.

CONCLUSIONS

Using an indirect nonparametric approach, this study proposes new percentiles for parameters from concomitant arterial and venous umbilical cord blood gases.

Understanding Fetal Heart Rate Patterns That May Predict Antenatal and Intrapartum Neural Injury

Electronic fetal heart rate (FHR) monitoring is widely used to assess fetal well-being throughout pregnancy and labor. Both antenatal and intrapartum FHR monitoring are associated with a high negative predictive value and a very poor positive predictive value. This in part reflects the physiological resilience of the healthy fetus and the remarkable effectiveness of fetal adaptations to even severe challenges. In this way, the majority of "abnormal" FHR patterns in fact reflect a fetus' appropriate adaptive responses to adverse in utero conditions. Understanding the physiology of these adaptations, how they are reflected in the FHR trace and in what conditions they can fail is therefore critical to appreciating both the potential uses and limitations of electronic FHR monitoring.

Arterio-venous blood gas Δvalues for validation of umbilical cord blood samples at birth are not only biased by sample mix ups but also affected by clinical factors

INTRODUCTION

Traditional validation of umbilical cord blood samples with positive veno-arterial ΔpH and arterio-venous ΔpCO₂ values confirms the source of samples, whereas negative Δvalues represent mix-up of samples. To investigate whether this is true, the distributions of V-A ΔpO₂ and A-V Δlactate were also explored and related to clinical characteristics. In addition, different cord blood sampling techniques were evaluated.

MATERIAL AND METHODS

Register study with cord blood acid-base and clinical data from 27 233 newborns. Clinical characteristics were related to positive, zero and negative Δvalues. Blood samplings from unclamped and double-clamped cords were compared. A two-sided P < 0.05 was considered significant.

RESULTS

ΔpH and ΔpCO₂ values distributed into positive, around zero, and negative sub-populations, with significant differences in pH and clinical characteristics between sub-populations. No such sub-populations were distinguished for ΔpO₂ and Δlactate. The 2.5th and 5th ΔpH percentiles were 0.013 and 0.022, respectively, and for ΔpCO₂ 0.30 and 0.53 kPa. Applying 5th percentile criteria resulted in 3.5% of "approved" cases showing a ΔpO₂  ≤ 0. Puncture and sampling of the unclamped cord resulted in significantly better sample quality.

CONCLUSIONS

Unphysiological negative ΔpO₂ values occurred despite correct validation with traditional criteria. Δlactate cannot be used for validation because both positive and negative values are physiological. Positive/around zero/negative ΔpH and ΔpCO₂ sub-populations were associated with significant differences in pH and clinical characteristics, indicating that defective sampling and sample handling are not the sole explanations for negative Δvalues. Prompt puncture and sampling of the unclamped cord resulted in best sample quality.

The peripheral chemoreflex: indefatigable guardian of fetal physiological adaptation to labour

The fetus is consistently exposed to repeated periods of impaired oxygen (hypoxaemia) and nutrient supply in labour. This is balanced by the healthy fetus's remarkable anaerobic tolerance and impressive ability to mount protective adaptations to hypoxaemia. The most important mediator of fetal adaptations to brief repeated hypoxaemia is the peripheral chemoreflex, a rapid reflex response to acute falls in arterial oxygen tension. The overwhelming majority of fetuses are able to respond to repeated uterine contractions without developing hypotension or hypoxic-ischaemic injury. In contrast, fetuses who are either exposed to severe hypoxaemia, for example during uterine hyperstimulation, or enter labour with reduced anaerobic reserve (e.g. as shown by severe fetal growth restriction) are at increased risk of developing intermittent hypotension and cerebral hypoperfusion. It is remarkable to note that when fetuses develop hypotension during such repeated severe hypoxaemia, it is not mediated by impaired reflex adaptation, but by failure to maintain combined ventricular output, likely due to a combination of exhaustion of myocardial glycogen and evolving myocardial injury. The chemoreflex is suppressed by relatively long periods of severe hypoxaemia of 1.5-2 min, longer than the typical contraction. Even in this setting, the peripheral chemoreflex is consistently reactivated between contractions. These findings demonstrate that the peripheral chemoreflex is an indefatigable guardian of fetal adaptation to labour.

Delayed Umbilical Cord Clamping in the 21st Century: Indications for Practice

BACKGROUND

Health care providers have debated the timing of umbilical cord clamping since the days of Aristotle. Delayed cord clamping was the mainstay of practice until about the 1950s when it was changed to immediate clamping on the basis of a series of blood volume studies combined with the introduction of active management of the third stage of labor. However, in recent years, several systematic reviews advise that delayed cord clamping should be used in all births for at least 30 to 60 seconds.

PURPOSE

The purpose of this article is to discuss the physiology of umbilical cord clamping, the potential benefits and adverse effects of delayed cord clamping, and how this affects the advanced practice nurse.

SEARCH STRATEGY

A search of PubMed, Cochrane Reviews, and Clinical Key was used to find relevant research on the topic of umbilical cord clamping.

RESULTS

Potential benefits of delayed cord clamping include decreased frequency of iron-deficiency anemia in the first year of life with improved neurodevelopmental outcomes in term infants, reduced need for blood transfusions, possible autologous transfusion of stem cells, and a decreased incidence of intraventricular hemorrhage. Apprehension exists regarding the feasibility of the practice as well as the potential hindrance of immediate resuscitation.

IMPLICATIONS FOR PRACTICE

There is a need to begin to look for populations for which delayed cord clamping can be implemented.

IMPLICATIONS FOR FUTURE RESEARCH

Recommendations are inconsistent on the patient population and timing; therefore, further studies are needed to understand the multiple variables that affect timing of umbilical cord clamping.

Correlating multidimensional fetal heart rate variability analysis with acid-base balance at birth

Fetal monitoring during labour currently fails to accurately detect acidemia. We developed a method to assess the multidimensional properties of fetal heart rate variability (fHRV) from trans-abdominal fetal electrocardiogram (fECG) during labour. We aimed to assess this novel bioinformatics approach for correlation between fHRV and neonatal pH or base excess (BE) at birth.We enrolled a prospective pilot cohort of uncomplicated singleton pregnancies at 38-42 weeks' gestation in Milan, Italy, and Liverpool, UK. Fetal monitoring was performed by standard cardiotocography. Simultaneously, with fECG (high sampling frequency) was recorded. To ensure clinician blinding, fECG information was not displayed. Data from the last 60 min preceding onset of second-stage labour were analyzed using clinically validated continuous individualized multiorgan variability analysis (CIMVA) software in 5 min overlapping windows. CIMVA allows simultaneous calculation of 101 fHRV measures across five fHRV signal analysis domains. We validated our mathematical prediction model internally with 80:20 cross-validation split, comparing results to cord pH and BE at birth.The cohort consisted of 60 women with neonatal pH values at birth ranging from 7.44 to 6.99 and BE from -0.3 to -18.7 mmol L(-1). Our model predicted pH from 30 fHRV measures (R(2) = 0.90, P < 0.001) and BE from 21 fHRV measures (R(2) = 0.77, P < 0.001).Novel bioinformatics approach (CIMVA) applied to fHRV derived from trans-abdominal fECG during labor correlated well with acid-base balance at birth. Further refinement and validation in larger cohorts are needed. These new measurements of fHRV might offer a new opportunity to predict fetal acid-base balance at birth.

Open access intrapartum CTG database

Background

Cardiotocography (CTG) is a monitoring of fetal heart rate and uterine contractions. Since 1960 it is routinely used by obstetricians to assess fetal well-being. Many attempts to introduce methods of automatic signal processing and evaluation have appeared during the last 20 years, however still no significant progress similar to that in the domain of adult heart rate variability, where open access databases are available (e.g. MIT-BIH), is visible. Based on a thorough review of the relevant publications, presented in this paper, the shortcomings of the current state are obvious. A lack of common ground for clinicians and technicians in the field hinders clinically usable progress. Our open access database of digital intrapartum cardiotocographic recordings aims to change that.

Description

The intrapartum CTG database consists in total of 552 intrapartum recordings, which were acquired between April 2010 and August 2012 at the obstetrics ward of the University Hospital in Brno, Czech Republic. All recordings were stored in electronic form in the OB TraceVue®;system. The recordings were selected from 9164 intrapartum recordings with clinical as well as technical considerations in mind. All recordings are at most 90 minutes long and start a maximum of 90 minutes before delivery. The time relation of CTG to delivery is known as well as the length of the second stage of labor which does not exceed 30 minutes. The majority of recordings (all but 46 cesarean sections) is – on purpose – from vaginal deliveries. All recordings have available biochemical markers as well as some more general clinical features. Full description of the database and reasoning behind selection of the parameters is presented in the paper.

Conclusion

A new open-access CTG database is introduced which should give the research community common ground for comparison of results on reasonably large database. We anticipate that after reading the paper, the reader will understand the context of the field from clinical and technical perspectives which will enable him/her to use the database and also understand its limitations.

Association between umbilical cord artery pCO₂ and the Apgar score; elevated levels of pCO₂ may be beneficial for neonatal vitality after moderate acidemia

OBJECTIVE

To determine the association between 5-min Apgar score and umbilical cord artery carbon dioxide tension (pCO₂).

DESIGN

Observational study.

SETTING

European hospital labor wards.

POPULATION

Data from 36,432 newborns ≥36 gestational weeks were obtained from three sources: two trials of monitoring with fetal electrocardiogram (the Swedish randomized controlled trial and the European Union Fetal ECG trial) and Mölndal Hospital data. After validation of the acid-base values, 25,806 5-min Apgar scores were available for analysis.

METHODS

Validation of the umbilical cord acid-base values was performed to obtain reliable data. 5-min Apgar score was regressed against cord artery pCO₂ in a polynomial multilevel model.

MAIN OUTCOME MEASURES

Five-min Apgar score, umbilical cord pCO₂, pH, and base deficit.

RESULTS

Overall, a higher cord artery pCO₂ was found to be associated with lower 5-min Apgar scores. However, among newborns with moderate acidemia, lower umbilical cord artery pCO₂ (≤median pCO₂ for the specific cord artery pH) was associated with lower 5-min Apgar scores, with a relative risk of 2.0 (95% confidence interval: 1.4-2.8) for 5-min Apgar scores 0-6.

CONCLUSIONS

Metabolic acidosis affects the newborn's vitality more than respiratory acidosis. In addition, elevated levels of pCO₂ may be beneficial for fetuses with moderate acidemia, and thus cord artery pCO₂ is a factor that should be considered when assessing the compromised newborn.

Effects of delayed compared with early umbilical cord clamping on maternal postpartum hemorrhage and cord blood gas sampling: a randomized trial

OBJECTIVE

To investigate the effect of delayed cord clamping (DCC) compared with early cord clamping (ECC) on maternal postpartum hemorrhage (PPH) and umbilical cord blood gas sampling.

DESIGN

Secondary analysis of a parallel-group, single-center, randomized controlled trial.

SETTING

Swedish county hospital.

POPULATION

382 term deliveries after a low-risk pregnancy.

METHODS

Deliveries were randomized to DCC (≥180 seconds, n = 193) or ECC (≤10 seconds, n = 189). Maternal blood loss was estimated by the midwife. Samples for blood gas analysis were taken from one umbilical artery and the umbilical vein, from the pulsating unclamped cord in the DCC group and from the double-clamped cord in the ECC group. Samples were classified as valid when the arterial-venous difference was -0.02 or less for pH and 0.5 kPa or more for pCO2 . Main outcome measures. PPH and proportion of valid blood gas samples.

RESULTS

The differences between the DCC and ECC groups with regard to PPH (1.2%, p = 0.8) and severe PPH (-2.7%, p = 0.3) were small and non-significant. The proportion of valid blood gas samples was similar between the DCC (67%, n = 130) and ECC (74%, n = 139) groups, with 6% (95% confidence interval: -4%-16%, p = 0.2) fewer valid samples after DCC.

CONCLUSIONS

Delayed cord clamping, compared with early, did not have a significant effect on maternal postpartum hemorrhage or on the proportion of valid blood gas samples. We conclude that delayed cord clamping is a feasible method from an obstetric perspective.

The relationship between umbilical cord arterial pH and serious adverse neonatal outcome: analysis of 51,519 consecutive validated samples

OBJECTIVE

To examine the relationship between umbilical cord pH at term and serious neonatal outcomes.

DESIGN

Observational cohort study.

SETTINGS

Deliveries within the Oxford Radcliffe Hospital NHS Trust between 1991 and 2009.

POPULATION

In all, 51,519 singleton, term, nonanomalous live neonates with validated umbilical cord arterial pH values.

METHODS

Absolute risks, relative risks with 95% confidence intervals, and numbers needed to harm were calculated for different levels of arterial pH across the entire range.

MAIN OUTCOME MEASURES

Neonatal encephalopathy with seizures and/or death, encephalopathy within 24 hours of birth, 5-minute Apgar scores and neonatal unit admission.

RESULTS

The median arterial pH was 7.22, interquartile range 7.17-7.27. The absolute risk of an adverse neurological outcome was significantly increased below 7.10 (0.36%) and was lowest between 7.26 and 7.30 (0.16%). Even below 7.00, the risk was only 2.95%. However, more than 75% of neonates with neurological outcomes examined, including seizures within 24 hours of birth, had a pH above 7.10. A small increase in risk was evident at higher pH levels.

CONCLUSION

The threshold pH for adverse neurological outcomes is 7.10 and the 'ideal' cord pH is 7.26-7.30. Above 7.00, however, neonatal acidaemia is weakly associated with adverse outcomes. Most neonates with neurological morbidity have normal cord pH values. Other variables must influence adverse outcomes and account for more of these than acidaemia. A better understanding of these is required before intrapartum fetal monitoring can improve.

How does the duration of active pushing in labor affect neonatal outcomes?

AIM

To assess the effect of time of active pushing (TAP) on neonatal outcome.

MATERIALS AND METHODS

The study population (n=36,432) was taken from a Swedish randomized control trial on intrapartum monitoring, a European Union fetal electrocardiogram trial, and from Mölndal Hospital. After validation of acid-base samples and TAP, 22,812 cases were accepted for analysis.

RESULTS

The median active TAP was 36 min for P0 and 13 min for P≥1 (P<0.001). After adjustments for parity, epidural, labor induction, birth weight, and gender, pushing for 15-29 min (n=6589) relative to pushing for <15 min (n=7264) increased the OR of a cord artery pH of <7.00 to 3.20 (95% CI 1.7-6.0), and that of a base deficit in extracellular fluid of >12 mmol/L to 3.5 (95% CI 1.3-9.0). The group with a cord artery pH of <7.00 had a longer TAP than the group with pH≥7.00: median (5th-95th percentile), 38 (9-107) min vs. 23 (5-87) min, P<0.001. The probability of a spontaneous vaginal delivery decreased significantly with every subsequent increase of 30 min in TAP (P<0.05).

CONCLUSION

The risks of severe acidemia, metabolic acidosis, and deteriorated neonatal outcome gradually increased with the length of TAP (>15 min), while the probability of a spontaneous vaginal delivery decreased with the duration of pushing. We suggest active physiological evaluation of the labor progress together with continuous electronic fetal monitoring during pushing irrespective of guideline thresholds.