[Umbilical blood pH, Apgar scores, and early neonatal mortality]

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.

Maternal Prepregnancy Obesity Affects Foetal Growth, Birth Outcome, Mode of Delivery, and Miscarriage Rate in Austrian Women

The increasing obesity rates among women of reproductive age create a major obstetrical problem as obesity during pregnancy is associated with many complications, such as a higher rate of caesarean sections. This medical record-based study investigates the effects of maternal prepregnancy obesity on newborn parameters, birth mode, and miscarriage rate. The data of 15,404 singleton births that had taken place between 2009 and 2019 at the public Danube Hospital in Vienna were enrolled in the study. Newborn parameters are birth weight, birth length, head circumference, APGAR scores, as well as pH values of the arterial and venous umbilical cord blood. In addition, maternal age, height, body weight at the beginning and the end of pregnancy, and prepregnancy body mass index (BMI) (kg/m²) have been documented. The gestational week of birth, the mode of delivery, as well as the number of previous pregnancies and births, are included in the analyses. Birth length, birth weight, and head circumference of the newborn increase with increasing maternal BMI. Furthermore, with increasing maternal weight class, there tends to be a decrease in the pH value of the umbilical cord blood. Additionally, obese women have a history of more miscarriages, a higher rate of preterm birth, and a higher rate of emergency caesarean section than their normal-weight counterparts. Consequently, maternal obesity before and during pregnancy has far-reaching consequences for the mother, the child, and thus for the health care system.

Point-of-care assessment of combined umbilical arterial and venous lactate: A potential screening test for neonatal acidosis

OBJECTIVE

To examine the relationship between point-of-care (POC) measurement of combined umbilical arterial and venous (CUAV) lactate and umbilical artery (UA) lactate to determine whether POC assessment of this sample could be an alternative screening modality for neonatal acidosis and aid prediction of neonatal morbidity.

METHODS

In this cross-sectional pilot study, UA and CUAV cord blood samples were collected from live, singleton neonates delivered between June and August 2019, at a tertiary care center. UA samples were analyzed for pH and lactate using a blood gas analyzer. CUAV lactate was also assessed on a blood gas analyzer and at the POC. Linear regression was used to determine the correlation between these samples.

RESULTS

A total of 152 neonates were included. There was a statistically significant correlation between CUAV lactate concentrations and UA lactate concentrations (R²  = 0.744). Additionally, CUAV lactate concentration measured at the POC was significantly correlated with that measured on a traditional blood gas analyzer (R²  = 0.928).

CONCLUSION

POC testing of CUAV lactate is reliable and closely correlated with UA lactate concentrations, making POC testing of CUAV lactate a potential screening test for neonatal acidosis. More data are needed to establish standardization of this test relative to its predictive value in clinical neonatal outcomes.

[Critical Outcome and Hypoxic Ischemic Encephalopathy - A quality Assurance Issue]

The study evaluates the predictive value of the critical status of a newborn as to the risk of developing hypoxic ischemic encephalopathy (HIE).

METHODS

On the basis of the data set from the perinatal survey in Hesse, Germany, in the year 2016, including 52,122 live births (singleton, 37+0 GA), cases of critical newborns were identified. A conjoined analysis with the data set of the neonatal survey from the identical period provided the basis to evaluate the relationship to cases compromised by HIE.

RESULTS

The incidence of cases with a critical outcome (n=11) and those with HIE (n=29) was low. The sensitivity of the status of the newborn for detecting a risk of HIE was 10.34%. The specificity was 99.98%. The positive predictive value was 27.35%. The negative predictive value was 99.95%. The detailed, confidential single-case analysis indicated the ability to avoid negative outcomes in about one third of cases with a critical status of the newborn (4/11) and HIE (9/29).

DISCUSSION AND CONCLUSION

The likelihood of developing encephalopathy (HIE) increases after a critical outcome after birth. Intensified monitoring of these newborns is justified. A single-case analysis identifies the potential ways to improve perinatal outcomes. Measures of external quality assurance should integrate the analysis of both perinatal and neonatal surveys as a basis for quality management (QM).

Decision-to-Delivery Time and Perinatal Complications in Emergency Cesarean Section

BACKGROUND

A decision-to-delivery interval (DDI) of no more than 20 minutes has long been considered a requirement for cesarean sections, even though there have hardly been any studies on this topic. We retrospectively investigated data relevant to DDI for emergency cesarean sections performed for the most common indications, namely, suspected and documented fetal asphyxia.

METHODS

We analyzed data on emergency in-hospital cesarean sections in the period 2008-2015. Low 5- and 10-minute Apgar scores (a scheme with points awarded for breathing, heart rate, muscle tone, skin coloration, and the elicitability of reflexes) were the primary endpoints; acid-base status in arterial cord blood and in-hospital neonatal death were the secondary endpoints. The raw analysis was supplemented by an analysis adjusted for various factors including gestational age, maternal age, and obstetrical presentation.

RESULTS

Data from 39 291 neonates were included. The DDI was up to 10 minutes in 64.6% of cases, from 11 to 20 minutes in 34.3%, and over 20 minutes in 1.1%. Low Apgar scores were less common in children whose emergency cesarean sections were performed within 10 minutes or within 20 minutes. For example, the adjusted odds ratio for a 10-minute Apgar score below 4 was 0.49 (95% confidence interval [0.25; 0.96] when a DDI of more than 20 minutes was used as the reference criterion.

CONCLUSION

This is the largest population-based, risk-adjusted analysis to be carried out on this topic to date. It reveals, for the first time, an association between DDI of 20 minutes or less and the avoidance of outcomes that are dangerous to the child. As it is not possible to predict such obstetrical emergencies in advance, it seems reasonable to ensure the availability of caredelivery structures that make it possible for emergency cesarean sections to be performed within 20 minutes of the decision to do so.

Obstetric risk factors for poor neonatal adaptation at birth

PURPOSE

To identify obstetric risk factors of delivering a neonate with poor neonatal adaptation at birth.

MATERIAL AND METHODS

Nested case-control study. Poor neonatal adaptation was defined for presence of at least: umbilical cord artery pH <7.10, base deficit ≥12 mmol/L, Apgar score at 1' ≤5. Controls were selected from the same population and matched with cases. The association between clinical parameters and poor neonatal adaptation was analyzed by logistic regression.

RESULTS

One hundred and thirty three women (2.1% of all live births) with a neonate presenting a poor neonatal adaptation were matched with 133 subsequent controls. Significant contributions for the prediction of poor neonatal adaptation were provided by maternal age ≥35 years (p ≤ .001, odds ratio (OR) 3.9 [95%CI: 2.3-6.8]), nulliparity (p ≤ .001, OR 3.3 [95%CI: 1.8-6]), complications during pregnancy (p = .032, OR 2.2 [95%CI: 1.1-4.4]), gestational age at delivery <37 weeks (p = .008, OR 5.2 [95%CI: 1.5-17.8]) and cardiotocography category II or III (p ≤ .001, OR 36.3 [95%CI: 16.5-80.1]). The receiver operative characteristic curve was 0.91 [95%CI: 0.87-0.95], and detection rates 82.7% and 89.5% at 10% and 20% of false positive rates, respectively.

CONCLUSIONS

Several obstetric risk factors before and during labor can identify a subgroup of newborns at higher risk of a poor neonatal adaptation at birth.

Strength of association between umbilical cord pH and perinatal and long term outcomes: systematic review and meta-analysis

OBJECTIVE

To evaluate the association between umbilical cord pH at birth and long term outcomes.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Medline (1966-August 2008), Embase (1980-August 2008), the Cochrane Library (2008 issue 8), and Medion, without language restrictions; reference lists of selected articles; and contact with authors.

STUDY SELECTION

Studies in which cord pH at birth was compared with any neonatal or long term outcome. Cohort and case-control designs were included.

RESULTS

51 articles totalling 481 753 infants met the selection criteria. Studies varied in design, quality, outcome definition, and results. Meta-analysis carried out within predefined groups showed that low arterial cord pH was significantly associated with neonatal mortality (odds ratio 16.9, 95% confidence interval 9.7 to 29.5, I(2)=0%), hypoxic ischaemic encephalopathy (13.8, 6.6 to 28.9, I(2)=0%), intraventricular haemorrhage or periventricular leucomalacia (2.9, 2.1 to 4.1, I(2)=0%), and cerebral palsy (2.3, 1.3 to 4.2, I(2)=0%).

CONCLUSIONS

Low arterial cord pH showed strong, consistent, and temporal associations with clinically important neonatal outcomes that are biologically plausible. These data can be used to inform clinical management and justify the use of arterial cord pH as an important outcome measure alongside neonatal morbidity and mortality in obstetric trials.

Mary Crosse project: systematic reviews and grading the value of neonatal tests in predicting long term outcomes

Background

Events before birth, condition at birth, events immediately following birth, and condition in early childhood are linked together, and have implications for health and disease in adulthood. At present, there is lack of clarity about the tests that purport to link these various stages. This is partly because there is paucity of collated information about the best strategies for predicting longer-term outcomes before (using tests in fetal period) or after birth (using tests in neonatal period, infancy as well as early childhood).

Methods/Design

A series of systematic reviews and meta-analyses will be undertaken to determine, amongst neonates, the ability of various tests and measures to predict infant, childhood and adult outcomes. We will search Medline, Embase, Cochrane Library, MEDION, citation lists of review articles and eligible primary articles and will contact experts in the field. Independent reviewers will select studies, extract data and assess study quality according to established criteria. Language restrictions will not be applied. Data synthesis will involve meta-analysis (where appropriate), exploration of heterogeneity and publication bias. Evidence collated will be graded for its quality to support decision making.

Discussion

The project will collate, synthesise and evaluate the available evidence concerning the value of tests of neonatal wellbeing to predict long term outcomes. The systematic reviews will assess the quality of available evidence and identify tests with the strongest association with outcomes, and assess their economic value. The output of this project will help formulate practice recommendations.

Examining the influence of maternal bradycardia on neonatal outcome using automated data collection

BACKGROUND

Due to the increasing number of caesarean sections, we investigated the influence of maternal bradycardia during general and regional anaesthesia on seven standard paediatric outcome parameters using our online recorded data.

METHODS

Data from 1154 women undergoing caesarean section were investigated prospectively. Bradycardia was defined as a heart rate below 60 beats/min. The matched-pairs method was used to evaluate the impact of bradycardia on Apgar scores at 1, 5, and 10 min, umbilical artery pH and base excess, admission to paediatric intensive care unit, and seven-day mortality. Matched references were automatically selected among all patients from the data pool according to anaesthetic technique, sensory block height, urgency, maternal age and body mass index. Stepwise regression models were developed to predict the impact of intra-operative bradycardia on outcome variables with differences between matched pairs assessed using univariate analysis.

RESULTS

Bradycardia was found in 146 women (12.7%) for whom a control could be matched in 131 cases (89.7%). Mean 5-minute Apgar score was 9.2+/-1.1 for study patients and 9.3+/-1.1 for controls. pH and base excess were not significantly different between groups. In cases of urgent surgery, neonates had an increased risk of 1.8 (95% CI 1.36-2.44, P<0.01) for an Apgar score <or= 8 at 1 min and a 2.6-fold risk (95% CI 1.64-4.06, P<0.01) of umbilical arterial pH of <or= 7.2 compared to infants undergoing non-urgent procedures.

CONCLUSIONS

Using matched-pairs analysis we were unable to demonstrate that episodes of maternal bradycardia below 60 beats/min were associated with a poorer neonatal outcome regardless of anaesthetic technique.