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Background The 10-point Apgar score has been used to assess the condition and prognosis of newborn infants throughout the world for almost 50 years. Some investigators have proposed that measurement of pH in umbilical-artery blood is a more objective method of assessing newborn infants.
Methods We carried out a retrospective cohort analysis of 151,891 live-born singleton infants without malformations who were delivered at 26 weeks of gestation or later at an inner-city public hospital between January 1988 and December 1998. Paired Apgar scores and umbilical-artery blood pH values were determined for 145,627 infants to assess which test best predicted neonatal death during the first 28 days after birth.
Results For 13,399 infants born before term (at 26 to 36 weeks of gestation), the neonatal mortality rate was 315 per 1000 for infants with five-minute Apgar scores of 0 to 3, as compared with 5 per 1000 for infants with five-minute Apgar scores of 7 to 10. For 132,228 infants born at term (37 weeks of gestation or later), the mortality rate was 244 per 1000 for infants with five-minute Apgar scores of 0 to 3, as compared with 0.2 per 1000 for infants with five-minute Apgar scores of 7 to 10. The risk of neonatal death in term infants with five-minute Apgar scores of 0 to 3 (relative risk, 1460; 95 percent confidence interval, 835 to 2555) was eight times the risk in term infants with umbilical-artery blood pH values of 7.0 or less (relative risk, 180; 95 percent confidence interval, 97 to 334).
Conclusions The Apgar scoring system remains as relevant for the prediction of neonatal survival today as it was almost 50 years ago.
The value of the Apgar score has become controversial because of attempts to use it as a predictor of the neurologic development of the infant, a use for which it was never intended.4 For example, the use of the Apgar score to identify birth asphyxia is a misapplication, since conditions such as congenital anomalies, preterm birth, and administration of drugs to the mother can result in low scores that are not reflective of asphyxia.5 Subsequently, measurement of umbilical-artery blood pH has been widely adopted in the United States as an adjunct to the Apgar score for assessing the condition of newborn infants.6,7,8 The Committee on Obstetric Practice of the American College of Obstetricians and Gynecologists, in concert with the American Academy of Pediatrics, has issued a publication entitled "Use and Abuse of the Apgar Score" in an effort to emphasize the limitations of the Apgar system in identifying birth asphyxia and predicting neurologic outcome.9,10
We undertook this study to examine whether the original intent of the Apgar system, to predict survival during the neonatal period,11 remains pertinent almost 50 years after the introduction of the system into American obstetrical and pediatric practice.
Methods
Study Design
Selected obstetrical outcomes for all women who give birth at Parkland Hospital, Dallas, as well as the neonatal outcomes, are entered into a computerized data base. Nurses attending each delivery complete an obstetrical data sheet, and research nurses assess the data for consistency and completeness before they are stored electronically. Data on infants' outcomes are abstracted from discharge records. Parkland Hospital is a tax-supported institution serving Dallas County that has a level III neonatal intensive care unit12 adjacent to the labor and delivery units. The obstetrics service is staffed by house officers and faculty members of the Department of Obstetrics and Gynecology at the University of Texas Southwestern Medical School, and the neonatology service is staffed by house officers and faculty members of the Department of Pediatrics.
Between January 1988 and December 1998, a total of 151,891 women delivered live-born singleton infants with gestational ages of 26 weeks or greater at Parkland Hospital. Infants less than 26 weeks of gestational age were excluded because their intrapartum treatment might have been influenced by concern about viability. Infants with major malformations identified by the time of discharge or at autopsy were also excluded. In all live-born infants, umbilical-artery blood samples were routinely drawn from a doubly clamped segment of the umbilical cord into heparinized 3-ml syringes and placed in ice for transport to the hospital laboratory for the measurement of blood gases and pH. The results were linked to the perinatal data base. Similarly, Apgar scores at one and five minutes were routinely assigned to all live-born infants, either by the nurses attending normal deliveries at term or by third-year pediatric house officers attending high-risk deliveries. The latter included all deliveries at less than 36 weeks of gestation and term deliveries with risk factors such as cesarean or forceps delivery, maternal fever during labor, and meconium-stained amniotic fluid. In addition, a resuscitation team consisting of a specially trained nurse from the neonatal intensive care unit, a respiratory therapist, and a fellow in neonatology was immediately available.
The outcome of interest was neonatal death during the first 28 days after birth. Preterm infants were defined as those born between 26 and 36 weeks of gestation, and term infants were defined as those born at or after 37 weeks of gestation. The gestational age assigned to each infant was based on the obstetrical estimate that was used to manage the care of the mother during the intrapartum period.
Statistical Analysis
All analyses were performed with SAS software (version 8.0, SAS Institute, Cary, N.C.). The Mantel–Haenszel chi-square test for trend and the chi-square goodness-of-fit test were used for categorical data. Relative risks and 95 percent confidence intervals were calculated by the Mantel–Haenszel method. Continuous data are presented as means ±SD. All P values were derived from two-sided tests.
Results
Paired Apgar scores and umbilical-artery blood gas values (pH, partial pressure of carbon dioxide, partial pressure of oxygen, bicarbonate concentration, and base deficit) were available for 145,627 infants, of whom 13,399 (9 percent) were delivered before term and 132,228 (91 percent) were delivered at term. Of the infants whose outcomes are described in this report, 58 percent (84,122) were Hispanic, 26 percent (38,255) were black, 13 percent (19,174) were white, and 3 percent (4076) were of other racial or ethnic backgrounds. The mean maternal age was 24±6 years; 3 percent (3974) of the women were under the age of 16, and 4 percent (6498) were 35 years of age or older. A total of 56,391 women (39 percent) were delivering their first child.
The incidence and relative risk of neonatal death in preterm infants according to their Apgar scores at five minutes are shown in Table 1. The incidence of neonatal death was 315 per 1000 preterm infants with five-minute Apgar scores of 0 to 3 but only 5 per 1000 for those with five-minute Apgar scores of 7 or greater (relative risk, 59; 95 percent confidence interval, 40 to 87). The incidence of neonatal death in preterm infants with five-minute Apgar scores of 4 to 6 was 72 per 1000 (relative risk, 13; 95 percent confidence interval, 9 to 20). The one-minute Apgar score was less useful in predicting neonatal death than the five-minute score (data not shown).
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In 1952, Apgar reported that neonatal survival through 28 days of age was related to the condition of the infant in the delivery room.1,3 Our analysis of the relation of five-minute Apgar scores to neonatal survival indicates that the Apgar score is just as meaningful today as it was almost 50 years ago. In both preterm and term infants, survival increased as Apgar scores increased. Among both preterm and term infants, those with five-minute Apgar scores of 0 to 3 had the highest risk of neonatal death. In term infants, the risk of neonatal death was 0.2 per 1000 for those with Apgar scores of 7 to 10, as compared with 244 per 1000 for those with scores of 0 to 3 at birth. This finding parallels the original results reported by Apgar.13 Although preterm infants had low five-minute Apgar scores that reflected gestational age, very low scores (0 to 3) were still associated with an increased risk of neonatal death. Moreover, these very low five-minute Apgar scores were related to the time of neonatal death in both preterm and term infants; specifically, neonatal deaths in infants with low scores occurred soon after birth.
The five-minute Apgar score was a better predictor of neonatal outcome than was measurement of umbilical-artery blood pH, even for newborn infants with severe acidemia. However, the combination of five-minute Apgar scores of 0 to 3 and umbilical-artery blood pH values of 7.0 or less increased the relative risk of death in both preterm and term infants.
The limitations of our analysis include the possibility that differences in the treatment of immature infants might influence the risk of neonatal death. For example, infants with very low Apgar scores who were delivered at 26 weeks of gestation might have been treated less aggressively than infants delivered at 26 weeks who had higher scores. However, the treatment approach used during the study was to provide all necessary support for infants delivered at 26 weeks of gestation or later.14 (Infants born before 26 weeks of gestation were not included in the study.)
Another limitation of this study is the small number of infants with very low five-minute Apgar scores. During a period of 11 years, five-minute Apgar scores of 0 to 3 were assigned to only 178 of the 145,627 infants born at our hospital who were included in our study. Nonetheless, our results suggest that very low five-minute scores, although rare, continue to be strongly predictive of early neonatal death. Finally, a potential ascertainment bias is caused by the exclusion of 6264 infants for whom umbilical-artery blood gas results were not available. Indeed, the incidence of neonatal death in this group of infants was 4.5 per 1000, as compared with 1.2 per 1000 (P=0.002) in infants for whom blood gas analyses were performed. However, an Apgar score of 0 to 3 at five minutes remained a significant predictor of neonatal death in both preterm and term infants, whether or not umbilical-blood gas analyses were available.
We cannot dispute the contemporary viewpoint that use of the Apgar score for the prediction of long-term neurologic outcome is inappropriate.4,9,10 However, the poor performance of the Apgar system as a predictor of neurologic development, a purpose for which it was never intended, should not undermine the continuing value of assigning Apgar scores to newborn infants. In our view, it should not be surprising that features of vital activity such as heart rate, respiration, and neuromuscular function reflect the prognosis for neonatal survival even in premature infants. We conclude that the Apgar system continues to be relevant to the prediction of neonatal outcome after almost half a century.
Source Information
From the Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas.
Address reprint requests to Dr. Casey at the Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390, or at brian.casey{at}utsouthwestern.edu.
References
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