Amniotic fluid and umbilical cord serum erythropoietin in term and prolonged pregnancies

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.

Endogenous erythropoietin at birth is associated with neurodevelopmental morbidity in early childhood

BACKGROUND

New biomarkers that predict later neurodevelopmental morbidity are needed. This study evaluated the associations between umbilical cord serum erythropoietin (us-EPO) and neurodevelopmental morbidity by the age of 2-6.5 years in a Finnish cohort.

METHODS

This study included 878 non-anomalous children born alive in 2012 to 2016 in Helsinki University Hospitals and whose us-EPO concentration was determined at birth. Data of these children were linked to data from the Finnish Medical Birth Register and the Finnish Hospital Discharge Register. Neurodevelopmental morbidity included cerebral palsy, epilepsy, intellectual disability, autism spectrum disorder, sensorineural defects, and minor neurodevelopmental disorders.

RESULTS

In the cohort including both term and preterm children, us-EPO levels correlated with gestational age (r = 0.526) and were lower in premature children. High us-EPO levels (>100 IU/l) were associated with an increased risk of severe neurodevelopmental morbidity (OR: 4.87; 95% CI: 1.05-22.58) when adjusted for the gestational age. The distribution of us-EPO levels did not differ in children with or without the later neurodevelopmental diagnosis.

CONCLUSIONS

Although high us-EPO concentration at birth was associated with an increased risk of neurodevelopmental morbidity in early childhood, the role of us-EPO determination in clinical use appears to be minor.

IMPACT

We determined whether endogenous umbilical cord serum erythropoietin would be a new useful biomarker to predict the risk of neurodevelopmental morbidity. This study evaluated the role of endogenous erythropoietin at birth in neurodevelopmental morbidity with a study population of good size and specific diagnoses based on data from high-quality registers. Although high umbilical cord serum erythropoietin concentration at birth was associated with an increased risk of neurodevelopmental morbidity in early childhood, the clinical value of erythropoietin determination appears to be minor.

Late-Pregnancy Fetal Hypoxia Is Associated With Altered Glucose Metabolism and Adiposity in Young Adult Offspring of Women With Type 1 Diabetes

OBJECTIVE

To investigate associations between exposure to fetal hypoxia and indicators of metabolic health in young adult offspring of women with type 1 diabetes (OT1D).

METHODS

156 OT1D born between 7/1995 and 12/2000 at Helsinki University Hospital, Finland, were invited for follow-up between 3/2019 and 11/2019. A control group of 442 adults born from non-diabetic pregnancies, matched for date and place of birth, was obtained from the Finnish Medical Birth Register. In total, 58 OT1D and 86 controls agreed to participate. All OT1D had amniotic fluid (AF) sampled for erythropoietin (EPO) measurement within two days before delivery in order to diagnose fetal hypoxia. In total, 29 OTID had an AF EPO concentration <14.0 mU/l, defined as normal, and were categorized into the low EPO (L-EPO) group. The remaining 29 OT1D had AF EPO ≥14.0 mU/ml, defined as fetal hypoxia, and were categorized into the high EPO (H-EPO) group. At the age of 18-23 years, participants underwent a 2-h 75g oral glucose tolerance test (OGTT) in addition to height, weight, waist circumference, body composition, blood pressure, HbA_1c, cholesterol, triglyceride, high-sensitivity CRP and leisure-time physical activity measurements.

RESULTS

Two OT1D were diagnosed with diabetes and excluded from further analyses. At young adult age, OT1D in the H-EPO group had a higher BMI than those in the L-EPO group. In addition, among female participants, waist circumference and body fat percentage were highest in the H-EPO group. In the OGTTs, the mean (SD) 2-h post-load plasma glucose (mmol/L) was higher in the H-EPO [6.50 (2.11)] than in the L-EPO [5.21 (1.10)] or control [5.67 (1.48)] offspring (p=0.009). AF EPO concentrations correlated positively with 2-h post-load plasma glucose [r=0.35 (95% CI: 0.07 to 0.62)] and serum insulin [r=0.44 (95% CI: 0.14 to 0.69)] concentrations, even after adjusting for maternal BMI, birth weight z-score, gestational age at birth and adult BMI. Control, L-EPO and H-EPO groups did not differ with regards to other assessed parameters.

CONCLUSIONS

High AF EPO concentrations in late pregnancy, indicating fetal hypoxia, are associated with increased adiposity and elevated post-load glucose and insulin concentrations in young adult OT1D.

Is obesity in pregnancy associated with signs of chronic fetal hypoxia?

INTRODUCTION

The prevalence of obesity in pregnancy is increasing worldwide. Maternal obesity increases risks of severe fetal and neonatal complications. The underlying pathophysiological mechanisms are unclear. One possible contributing factor could be chronic fetal hypoxia. The aim of this study was to compare placentas from women with and without obesity with respect to placental lesions, which could reflect compensatory mechanisms in response to chronic fetal hypoxia as well as lesions possibly leading to chronic fetal hypoxia. In addition, levels of erythropoietin in cord blood were compared between offspring of lean and obese women.

MATERIAL AND METHODS

This cohort study included 180 women with uneventful, full-term, singleton pregnancies, out of which 91 lean women had a body mass index (BMI) of 18.5-24.9 kg/m² and 89 women had obesity (BMI ≥30 kg/m² ). Women were recruited at Södersjukhuset between 16 October 2018 and 2 December 2019. Placentas were investigated by two senior perinatal pathologists, who were blinded for maternal BMI. Cord blood was analyzed for levels of erythropoietin.

RESULTS

Levels of erythropoietin in cord blood increased with maternal BMI (P = .01, β = 0.97, 95% CI 0.27-1.68). There was no difference between placentas of obese and lean women in number of placental lesions reflecting chronic fetal hypoxia or in lesions that could possibly lead to chronic fetal hypoxia.

CONCLUSIONS

This study of term and uneventful pregnancies demonstrated a positive association between maternal obesity and concentrations of erythropoietin in cord blood at birth. This finding supports the hypothesis of chronic fetal hypoxia as a risk factor for complications in the pregnancies of obese women. There were no differences in lesions associated with hypoxia between placentas of obese and lean women.