Intrauterine Asphyxia: Clinical Implications for Providers of Intrapartum Care

Jenifer Fahey, CNM, MSN, MPH; Tekoa L. King, CNM, MPH

Disclosures

J Midwifery Womens Health. 2005;50(6):498-506. 

In This Article

Newborn Assessment of Fetal Oxygenation/Acid-Base Status

Umbilical cord gases are used as an indicator of fetal oxygenation just prior to birth, and the Apgar score reflects newborn adaptation after birth. However, neither of these assessments is a reliable predictor of long-term neurologic outcome.

Apgar scores were created as a predictor of neonatal outcome and survival and are currently used to guide the need for neonatal resuscitation.[44] Although a 5-minute Apgar of ≤3 has been shown to be a good predictor of neonatal death, low 1- and 5-minute Apgar scores in infants who survive correlate poorly with intrapartum asphyxia and are poor predictors of long-term neurologic outcome.[45,46] Sykes et al. found that only 27% of newborns with an umbilical artery pH of <7.1 and base deficit of >12 mmol had a 1-minute Apgar of <7.[45] Nelson and Ellenberg analyzed outcomes of children from the Collaborative Perinatal Project through age 7, and demonstrated that newborns with Apgar scores of 0 to 3 at 5 minutes, whose score improves to 4 or better by 10 minutes, have less than a 1% chance of developing cerebral palsy.[46] Furthermore, 75% of children with cerebral palsy in this study had normal Apgar scores at birth.

Umbilical cord gases are used to evaluate a newborn's acid-base status. Normal values for umbilical cord gases vary, depending on how normality is defined in the population studied. Table 4 lists normal values for cord gases.[47,48,49,50,51]

Umbilical cord gases document the presence or absence of respiratory or metabolic acidemia in the newborn at the time of birth. Although traditionally an umbilical artery pH of <7.20 has been used to define acidemia, a statistically significant increase in the incidence of neonatal morbidity is not seen until the umbilical artery pH level is <7.0. In their study of 2738 live, term births, Gilstrap et al. found the incidence of morbidity increased in newborns with a cord pH <7.0 and whose Apgar scores at 1 and 5 minutes were ≤3.[48] All newborns with these findings required resuscitation, and half of them developed neurologic dysfunction. Evaluations of the relationship between umbilical cord gas values and subsequent neonatal morbidity were conducted after the study by Gilstrap was published.[49,50] A pure respiratory acidemia, defined by a pH of <7.20 in the presence of an elevated PCO2 and normal base deficit, is not generally associated with newborn morbidity in term infants.[51] The risk for complications increases in newborns with umbilical cord gas values that reflect a metabolic acidosis.[50,51] A study by Belai et al. confirms these findings and found that in infants with a pH of <7, an arteriovenous PCO2 difference of >25 mm Hg is a sensitive and specific parameter for identifying asphyxiated infants most likely to develop seizures, hypoxic-ischemic encephalopathy, and other abnormalities in the neonatal period.[52]

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