Pathologic fetal acidemia

There is no clearly established umbilical artery pH cutoff to be used for defining pathologic fetal acidemia (ie, the threshold associated with major neonatal morbidity or mortality). Classically, a pH cutoff of less than 7.20 has been used. Our goal was to define this pH cutoff more precisely. There were 3506 term newborns (2500 g or greater) with an umbilical artery pH of less than 7.20; these newborns were divided into five pH groups. Eighty-seven (2.5%) had a pH of less than 7.00, 95 (2.7%) a pH of 7.00-7.04, 290 (8.3%) 7.05-7.09, 798 (22.8%) 7.10-7.14, and 2236 (63.8%) 7.15-7.19. Two-thirds (66.7%) of the newborns with an umbilical artery pH less than 7.00 had a metabolic component in their acidemia, compared with 13.7% or less in all other pH groups. Significantly more (P less than .05) newborns in the less-than-7.00 pH group had low (less than 3) 1- and 5-minute Apgar scores compared with the other four pH groups. In addition, neonatal death was significantly more common (P = .03) in newborns with a pH less than 7.00, and seven (50%) of the 14 deaths occurred in this group. The statistically significant pH cutoff for all seizures was less than 7.05 (P = .004), and for unexplained seizures was less than 7.00 (P = .01). Eight (67%) of the 12 unexplained seizures occurred in this latter pH group. Thus, a more realistic pH cutoff for defining pathologic fetal acidemia would appear to be less than 7.00.     

Correlation of neonatal acid-base status with Apgar scores and fetal heart rate tracings

In this study the immediate neonatal acid-base status, obtained via a double-clamped segment of umbilical cord, in 75 term, singleton vaginal deliveries was compared to electronic fetal heart rate recordings and Apgar scores. Of 75 neonates, 59 had 1-minute Apgar scores greater than or equal to 7 and 52 had an initial pH greater than 7.20. Six of the 16 neonates with a 1-minute Apgar score less than 7 demonstrated a low pH (less than 7.20). At 5 minutes only eight of 75 neonates had Apgar scores less than 7 with six of the eight having pH values less than 7.20. Of those neonates with Apgar scores greater than or equal to 7 and pH less than 7.20 (seven neonates at 1 minute, two at 5 minutes), none had metabolic acidosis. Eighteen fetal heart rate tracings were considered abnormal; acidosis was confirmed in eight (44%) by pH criteria, yet only three of the eight neonates had low Apgar scores. Our investigations suggest that the combination of fetal heart rate monitoring, cord blood pH, and Apgar assessment is better than any one parameter alone as an evaluation of fetal status just after delivery.     

Outcomes among term infants when two-hour postnatal pH is compared with pH at delivery

OBJECTIVE: This study was undertaken to measure infant outcomes when pH at birth was compared with neonatal pH determined within 2 hours of age. STUDY DESIGN: We retrospectively studied term infants born between January 1, 1988, and August 31, 1998, who had umbilical artery blood pH measured at birth and again from the radial artery or umbilical artery within 2 hours after birth. Statistical significance was determined with the chi2 test. Odds ratios and 95% confidence intervals were calculated by means of the Mantel-Haenszel method. RESULTS: Data from a total of 1691 infants were analyzed: 178 (11%) had acidemia at birth (pH of <7.20) that persisted through the first 2 hours after birth; 110 (6%) had development of acidemia after birth; and 594 (35%) were born with a cord pH of <7.20 that improved after delivery. The remaining 809 infants (48%) did not have acidemia either at birth or during the neonatal period, and these served as the reference group. Seizures during the first 24 hours after birth were more likely among those infants with persistent acidemia (odds ratio, 13.0; 95% confidence interval, 6.3-26.7). The odds ratio for seizures among infants in whom acidemia developed after birth was 5.7 (95% confidence interval, 2.2-14.5). Other than the reference group, the infants who were born with acidemia that was corrected by 2 hours after birth had the lowest risk of seizures (odds ratio, 2.5; 95% confidence interval, 1.2-5.3). Significant differences in neonatal outcomes persisted after correction for anomalies. CONCLUSION: The direction of pH change from birth to the immediate neonatal period was significantly related to morbidity and mortality among term infants who were ill at birth or became ill shortly thereafter.     

Umbilical artery acid-base status in the preterm infant

It is becoming increasingly apparent that Apgar scores are generally lower in otherwise uncomplicated preterm newborns than in term newborns. However, there is little information regarding normal values for umbilical artery blood gas measurements in the preterm infant. The present study included 77 otherwise uncomplicated preterm infants and 1292 uncomplicated term infants. Although preterm infants did have significantly lower 1- and 5-minute Apgar scores, there was no significant difference in the frequency of acidemia (umbilical artery pH below 7.20). The mean pH was 7.29 in preterm infants and 7.28 in term infants. Mean values for pCO2, pO2, HCO3, and base deficit were similar in each group. There were no significant differences in umbilical artery blood gas values in the 77 preterm infants according to birth weight groups. Umbilical cord blood acid-base determination may prove a useful adjunct in assessing the condition of the newborn preterm infant.     

Asphyxial complications in the term newborn with severe umbilical acidemia.

OBJECTIVE: Our purpose was to determine the relationship of umbilical acid-base status and Apgar score to neonatal asphyxial sequelae in infants with severe acidemia (pH < 7.00). STUDY DESIGN: The obstetric and neonatal course of 129 term, nonanomalous singleton infants with umbilical pH < 7.00 was reviewed. RESULTS: There were three stillbirths (failed resuscitation). Seventy-two of 126 (57%) were admitted to the neonatal intensive care unit. Thirty-eight percent had pulmonary dysfunction, 26% renal dysfunction, 31% cardiac dysfunction, and 31% hypoxic ischemic encephalopathy (seizures and hypotonia, n = 29; seizures only, n = 3; hypotonia only, n = 10). There were five neonatal deaths. In 109 cases umbilical arterial values were available, and among these infants there was a significant increase in the incidence of seizures with declining pH from 9% (5/57), with a pH of 6.90 to 6.99, to 80% (8/10), with a pH of 6.61 to 6.70. Respiratory acidemia (PCO2 > 65, base deficit < 10) was identified in 28 of 109 (26%), all but six occurring in the pH range above 6.90. Compared with infants with comparable umbilical artery pH, infants with respiratory acidemia did not differ significantly with respect to asphyxial end-organ injury in general (8/35 vs 6/22), but there was a trend toward a lower incidence of hypoxic ischemic encephalopathy (6/35 vs 1/22, p = 0.06). All infants with definite abnormal outcome (five neonatal deaths and 10 severe neurologic deficit) had seizures, hypotonia, and at least one other organ system dysfunction. Twenty-four of 29 infants (83%) who developed seizures had a 5-minute Apgar score < 7, but only 12 of 29 (41%) had a 5-minute Apgar score of < or = 3. Two infants with Apgar scores of 6 and 7 at 5 minutes and no evidence of nonasphyxial comorbidity subsequently manifested profound neurologic deficit. CONCLUSIONS: Infants with severe umbilical acidemia can be separated with regard to risk of hypoxic ischemic encephalopathy and abnormal neurologic outcome by consideration of the severity and composition of the acidemia and evidence of other end-organ dysfunction. Even in this pH range the Apgar score is not highly predictive of asphyxial complications.     

Comparison of umbilical artery pH and 5-minute Apgar score in the low-birth-weight and very-low-birth-weight infant

The division between "normal" and low Apgar scores is based largely on data obtained from term newborns and may not apply to the premature infant. Umbilical artery pH has been suggested as a better indicator of intrapartum asphyxia. We examined the charts of 558 infants with birth weights less than or equal to 2500 gm with respect to umbilical artery pH, 5-minute Apgar scores, and birth weight percentiles. A positive correlation between birth weight and 5-minute Apgar score was noted. No such relationship existed between birth weight and umbilical artery pH. Within birth weight groups, small-for-gestational-age infants have higher Apgar scores and lower umbilical artery pH values than their appropriate-for-gestational age counterparts.     

Meconium in the amniotic fluid and fetal acid-base status

Of 323 pregnancies with meconium-stained amniotic fluid at 36-42 weeks' gestation, 68 (21%) had a pH less than 7.20 in umbilical arterial blood, 21 (7%) had a pH less than 7.15, and only three newborns (0.9%) had true metabolic acidemia. At birth, of the 74 newborns with normal electronic fetal heart rate (FHR) tracings, eight (11%) had an umbilical arterial pH less than 7.20. There was a significantly higher frequency of acidemia (defined as pH less than 7.20) in newborns with both baseline and periodic FHR abnormalities. Although there was a significant difference (P less than .05) in the frequency of meconium found below the cords in these neonates with an umbilical artery pH less than 7.20 compared with those with values exceeding 7.20, there was no significant difference in the frequency of clinical meconium aspiration syndrome. We conclude that meconium-stained amniotic fluid correlates poorly with infant condition at birth as reflected by umbilical cord acid-base measurements.     

Gestational age-dependent reference values for pH in umbilical cord arterial blood at term

OBJECTIVE: Despite a change of fetal physiologic and biochemical functions with gestational age, stationary umbilical cord acid-base reference values are used as measures of obstetric care quality. The aim of this study was to assess the risk of low Apgar score relative to low pH when using stationary versus gestational age-adjusted reference values. METHODS: Umbilical artery pH was determined in 24,390 term singleton vaginal deliveries with a 5-minute Apgar score of 9 or greater. Low pH was defined as less than 7.10 as a stationary cutoff value, whereas pH less than (mean - 2 standard deviations [SDs]) was used when gestational age was considered. The 5-minute Apgar score less than 7 at low pH was studied in 44,978 term deliveries. RESULTS: A significant negative correlation was found between gestational age and umbilical artery pH. The odds ratio (OR) for pH less than 7.10 was continuously increasing, from 0.6 at 37 weeks to 1.5 at 42 weeks. In contrast, the OR for pH less than (mean - 2 SDs) was steady until 42 weeks, whereafter it increased (OR 1.24; 95% confidence interval 1.05, 1.47). A linear decrease of the association between Apgar score less than 7 and pH less than 7.10 with increasing pregnancy duration was found (P =.097), but for pH less than (mean - 2 SDs) there was no such association. CONCLUSION: We found a physiologic linear decline of umbilical artery pH with gestational age at term. Gestational age-adjusted umbilical cord artery pH reference values result in fewer diagnoses of cord acidemia than a stationary cutoff of pH less than 7.10.     

Routine umbilical cord blood gas determinations?

Between 1986 and 1988, 1924 term nulliparous patients with spontaneous onset of labor were studied to assess the importance of obtaining umbilical cord blood gas levels on all deliveries. The umbilical cord arterial and venous pH values (expressed as mean +/- 2 SD) were 7.24 +/- 0.14 (n = 1694) and 7.32 +/- 0.12 (n = 1820), respectively. The incidence of newborn depression (1- or 5-minute Apgar score less than 7) was 14.1%; of these depressed newborns, the incidence of normal umbilical cord arterial pH values (greater than or equal to -2 SD) was 77.8%. Of the vigorous newborns, there was a 2.1% incidence of umbilical cord arterial blood acidemia. Umbilical cord arterial blood acidemia in vigorous newborns was not highly predictive of specific morbidity in the immediate newborn period. Regression analysis demonstrated the umbilical cord arterial pH to correlate best with the Apgar scores when compared with all other arterial or venous blood gas measurements. We reached the following conclusions: (1) that obtaining cord arterial pH values in vigorous newborns should be considered since the values will provide objective documentation or normal fetal acid base balance in 98% of infants. (2) Only a cord arterial pH determination is recommended since it reflects fetal or newborn status more accurately than all other measurements. Additional measurements increase the likelihood of abnormal results and do not contribute to neonatal management. (3) An umbilical cord blood pH value is extremely useful in ruling out the diagnosis of birth asphyxia in the depressed newborn.     

Diagnosis of birth asphyxia on the basis of fetal pH, Apgar score, and newborn cerebral dysfunction

Imprecise diagnosis of birth asphyxia coupled with uncertainties about causal factors for neurologic abnormalities in the newborn have greatly fueled the current litigation crisis in obstetrics. Our goal was to more precisely define birth asphyxia based on fetal condition as measured by umbilical artery blood pH, Apgar scores, and neurologic condition of newborns. We selected for study 2738 patients with singleton pregnancies with cephalic presentations who were delivered of infants at term to avoid complications such as prematurity, which may affect infant outcome independent of birth condition. The basis for study of these particular patients were defined criteria for high risk and an indicated arterial cord pH value. A total of five infants demonstrated cerebral dysfunction as evidenced by seizures during the neonatal period. Infection was linked to seizures in three of these infants; one infant had neonatal asphyxia and only one infant's clinical course could be attributed solely to birth events (uterine rupture). Stratification of umbilical artery blood pH values, Apgar scores, and combinations of these dependent variables in relation to newborn clinical outcomes revealed that infants must be severely depressed at delivery before birth asphyxia can be reliably diagnosed. Such depression includes Apgar scores less than or equal to 3 at 1 and 5 minutes plus umbilical artery pH values less than 7.00.     

Definition of intrapartum asphyxia and effects on outcome

Intrapartum asphyxia is defined as metabolic acidemia measured at birth with pH less than 7.00 and base deficit greater or equal to 12 mmol/l. Neonatal complications of intrapartum asphyxia include multiorgan failure and neonatal encephalopathy. Most severe consequences are death and neurological or sensorial impairment. Cause of permanent neurological impairment can be attributed to intrapartum asphyxia if three criteria are met: intrapartum history of a threatening event with acute fetal heart rate deterioration, biological markers of asphyxia, neonatal encephalopathy. Moderate to severe neonatal encephalopathy in asphyxiated term infants is associated with a high risk of cerebral palsy (especially quadriplegic or dyskinetic type) and/or cognitive disorders. Prognosis of neonatal encephalopathy can be accurately assessed by MR imaging.     

Status of infants at birth and risk for adverse neonatal events and long-term sequelae: a study in low birth weight infants

We evaluated the relationship of infant status at birth to neonatal morbidity and long-term development in 246 low birth weight infants (600 to 1750 gm). Nineteen percent of infants had 1-minute Apgar scores of less than or equal to 3, and 8% had an umbilical artery pH of less than or equal to 7.2. Acidosis was associated with an increased risk of grade 3 to 4 intracranial hemorrhage (odds ratio = 3.3). Low 1-minute Apgar score was associated with an increased risk of death (odds ratio = 4.8). Grade 3 to 4 intracranial hemorrhage was a strong risk factor for cerebral palsy among survivors (odds ratio = 16.1), as was low 1-minute Apgar score (odds ratio = 2.9). Only 15% of cases of cerebral palsy in this study were associated with acidosis at birth.     

Apgar scores and umbilical arterial pH in preterm newborn infants

One- and five-minute Apgar scores and umbilical cord arterial pH values were compared in preterm newborn infants of various gestational ages. The more premature the infant, the more likely the Apgar score was low in the presence of a pH greater than or equal to 7.25. Conversely, the closer to term, the more frequently an infant with a pH of less than 7.25 had an Apgar score of greater than or equal to 7. Therefore, in preterm infants, there is little congruity between the Apgar score and umbilical cord pH. Based on these findings, it is not appropriate to label preterm newborn infants as asphyxiated based on a low Apgar score.     

Acidemia at birth in the vigorous infant as a trigger incident to assess intrapartum care with regard to CTG patterns

Abstract

Objective: To evaluate if acidemia in vigorous infants is a useful variable in the assessement of intrapartm care with regard to cardiotocographic (CTG) patterns during the second stage.

Methods: Cases (n?=?241) were infants with an umbilical artery pH?<?7.05, controls (n?=?482) were infants with pH?≥?7.05. Apgar score was?≥7 at 5?min in both groups. CTGs during the last two hours of labor were assessed and neonatal outcomes compared. A sub-analysis of cases with metabolic acidemia: pH?<?7.00 and base deficit ≥12?mmol/L and acidemia: 7.00?<?pH?<?7.05 was performed.

Results: 63% of cases had a pathological CTG versus 26% of controls (p?<?0.001). Patterns with severe variable decelerations had a significantly longer duration in cases. Metabolic acidemia was significantly associated with severe variable decelerations and decreased variability. Infants to cases were admitted to neonatal care in 19% versus 2% of controls (p?<?0.001). With metabolic acidemia, 32% were admitted.

Conclusion: An umbilical artery pH?<?7.05 at birth of vigorous infants may be a useful variable for quality control of intrapartum management with regard to the assessment of second-stage CTGs. Differences in duration of pathological patterns indicate passiveness in acidemic cases.     

The relationship between Apgar score, umbilical artery pH and operative delivery for fetal distress in 2778 infants born at term

A total of 2778 infants born at term were studied to determine the relationship between Apgar scores after 1 min, umbilical artery pH values, mode of delivery, a diagnosis of fetal distress leading to operative delivery, and sex. Eighty-three percent of the population had normal Apgar scores (greater than or equal to 8) and normal pH values (greater than 7.15) in which 10% were operatively delivered for fetal distress (ODFD). Sixty-one percent of the children with low Apgar scores (less than or equal to 7) had normal pH values, and 74% of the infants with acidosis (pH less than or equal to 7.15) had normal Apgar score. Twenty-four percent of the infants with a low Apgar score and/or acidosis were ODFD (sensitivity). Ninety percent of the infants who had Apgar scores and pH values were not ODFD (specificity). The predictive value (a low Apgar score and/or acidosis) of ODFD was 33%, and the negative predictive value (normal Apgar score and a normal pH) of ODFD was 85%. A significantly higher incidence of ODFD and acidosis was found in boys.     

Impact of metabolic acidemia at birth on neonatal outcomes in infants born before 34 weeks’ gestation

Purpose: To examine prematurity-associated neonatal outcomes in early preterm infants with metabolic acidemia compared to those without such acidemia.

Methods: We performed a retrospective cohort analysis to assess the impact of metabolic acidemia on prematurity-associated complications in a large cohort of singleton live-born infants with complete umbilical cord gas analyses delivered between 24 0/7 and 33 6/7 weeks. Metabolic acidemia was defined as an umbilical artery pH less than 7.0 plus a base deficit of 12?mmol/L or greater. Outcomes were adjusted for gestational age using logistic regression.

Results: Between 1 January 1988 and 31 December 2014, 6970 singleton early preterm infants were delivered at our hospital, of which 126 (1.8%) had metabolic acidemia. Neonatal mortality as well as prematurity-associated morbidities were significantly increased in the presence of metabolic acidemia. Included were ventilator requirement (73% versus 36%, p?p?p?=?0.036), and neonatal death (13% versus 4%, p?Conclusion: Metabolic acidemia significantly increases the risks related to prematurity in infants delivered prior to 34 weeks’ gestation.     

Outcome of fetuses with lactic acidemia

Umbilical arterial lactate, pH, PO2, PCO2, and base deficit were measured at delivery of 468 live-born infants. The correlation between the 1-minute Apgar score and lactate (r = -0.34) was comparable to that between the 1-minute Apgar score and pH (r = 0.30). The multiple correlation coefficient between the 1-minute Apgar score and all five parameters combined (lactate, pH, PO2, PCO2, and base deficit) was 0.36. This was not significantly higher than the simple correlation coefficient for pH alone (0.30). Similar correlation coefficients were noted for the 5-minute Apgar score. The dividing point between normal and pathologic lactate levels was 3.70 mmol/L. A pH less than 7.20 and a lactate level greater than or equal to 3.70 mmol/L had the same sensitivity, specificity, and positive and negative predictive values for low Apgar scores (less than 7). While pH and lactate are equally correlated with fetal outcome, their combination with each other and with other blood gas parameters does not predict outcome better than either pH or lactate alone.     

Acid-base status at birth and neurodevelopmental outcome at four and one-half years

Two hundred thirty term infants with measured acid-base status in umbilical arterial blood at birth were selected from 1210 consecutive deliveries for detailed neurodevelopmental follow-up at age 4 1/2 years; 203 were examined. Cutoff points approximately 1 SD from the mean (pH less than or equal to 7.10; base deficit greater than 12 mmol/L) were used to define acidosis. No statistically significant associations between acidosis and developmental outcome were found. The highest proportion of unimpaired children was found among those who were most severely acidotic at birth (pH less than or equal to 7.04; 2 SD below mean), but this finding was not statistically significant. These findings suggest that the ability of the fetus to produce an acidosis in response to the stress of labor may be beneficial to long-term outcome. The 10 nonacidotic babies with 1-minute Apgar scores of less than or equal to 3 showed statistically significant deficits in some areas. Coincident acidosis was not associated with a worse outcome for infants with low Apgar scores.     

Nucleated red blood cell counts in term neonates with umbilical artery pH < or = 7.00

The purpose of this study was to determine whether nucleated red blood cell (NRBC) counts are elevated in term neonates who have severe fetal acidemia at birth. The neonatal NRBC counts of term (gestational age > or = 37 weeks) neonates with pathological acidemia were compared with those from control neonates who met the following criteria: gestational age > or = 37 weeks, birth weight > or = 2800 g, umbilical artery pH > or = 7.25, and a 5-minute APGAR > 7. Pathological acidemia was defined as an umbilical artery pH < or = 7.0 and a base excess > -12 mEq/L. Twenty-six neonates met all inclusion criteria and were compared to 78 controls. The mean NRBC/100 WBC was 11.9 +/- 13.5 (range 0 to 45) for acidemic neonates compared to 3.9 +/- 2.9 NRBC/100 WBC (range 0 to 11) for control neonates [p <0.001]. Our findings suggest that the onset of hypoxia-ischemia in pregnancies complicated by severe fetal acidemia often begins prior to the intrapartum period.     

Nucleated red blood cells as a marker of acidemia in term neonates.

OBJECTIVES: Nucleated red blood cells are produced in increased numbers under hypoxic conditions. We sought to examine the relationship between nucleated red blood cell count in the circulations of term neonates and other possible markers of fetal hypoxia. STUDY DESIGN: We prospectively collected umbilical blood from all live-born neonates delivered at our institution. Arterial blood was analyzed for pH and blood gas values. Venous blood was analyzed for nucleated red blood cell count. We reviewed the medical records for maternal data and neonatal outcomes of gestations of >/=37 weeks' duration. RESULTS: We evaluated 1561 cases. The mean nucleated red blood cell count per 100 white blood cells was 9.2 +/- 18.1 (range, 0-327). Nucleated red blood cell counts were higher in infants with pH <7.20 (P =.001). Both patients with respiratory acidemia and patients with uncompensated metabolic acidemia had elevated nucleated red blood cell counts (P =.013 and P =.014, respectively). As umbilical artery pH and base excess decreased, nucleated red blood cells became more prevalent. Elevated nucleated red blood cell counts were associated with presence of meconium (P =. 020) and neonatal intensive care unit admission (P =.024). CONCLUSIONS: We found that nucleated red blood cell counts vary widely in the circulation of term neonates. Elevated nucleated red blood cell counts are associated with fetal acidemia, meconium, and neonatal intensive care unit admission.