The Apgar score has been used worldwide to describe the health status of newborn babies. Since the early 1960’s an Apgar score from 0-3 has been defined as a low score, a score from 4-6 as a moderately low, and 7 to 10 as normal. Given how the score is constructed, one would expect it to describe risk in a linear manner. However the commonly accepted belief seems to be that the outcomes should be the same for scores 7 to 10, with outcomes dropping for lower scores in a step like manner.
In 2015, we decided to challenge this premise by exploring the role of the Apgar score as a continuous variable, across the entire spectrum of recorded scores. In a study conducted in Manitoba, Canada, we showed an association between the Apgar score and early childhood developmental vulnerability at five years of age, in a graded continuous manner. [1] This was not an expected finding, since until then there had not been a reason to consider that the domains of the Apgar score could have equal weight or that the scores of 7-9 could have long term adverse outcomes. However, the sample size of that study was not sufficient and we felt the need to replicate the findings.
I had a chance to revisit Apgar score when I started my Postdoctoral Fellowship at the Karolinska Institutet in Sweden using their nation-wide databases. I was examining the role of maternal early pregnancy BMI on the risk of epilepsy in offspring when I noticed in the data that there was an association between the Apgar score and the risk of developing epilepsy. [2] In this data the Apgar score was categorized in the conventional <7 categories (0-3, 4-6, 7-10).
This gave us the opportunity to reexamine our hypothesis in another setting using a larger study population. We found, not only that the risks of cerebral palsy and epilepsy were inversely associated with five minute and 10 minute Apgar scores across the entire range of Apgar scores, but also that even slight changes within the normal Apgar score range (7-10) from five to 10 minutes also influence the risk of developing cerebral palsy and epilepsy. [3] This was of particular interest as in many healthcare settings, neonatologists, midwives, and other care providers will assign the newborn a 10-minute Apgar score only when a low five minute Apgar score is noted. Back in Canada, in another population-based study, we found children with a 1-minute Apgar score in the normal range (7 to 10) had an increased risk of developmental vulnerability, if their Apgar score at 5 minutes was <10. Particularly noteworthy was a reduction in the Apgar score from 10 at 1 minute to 7-9 at 5 minutes, as this substantially increased the risk of developmental vulnerability. [4]
Thus, the question remains, why are babies born at term, with no malformations, who have Apgar scores within the normal range (i.e. with scores of 7, 8, and 9) at 1, 5 or 10 minutes, at higher risk of adverse long-term outcomes? Our findings of differential risks associated with Apgar scores within the normal range were unexpected insofar as it is commonly assumed that Apgar scores of 9 and 10 are assigned arbitrarily. However, if Apgar scores of 7, 8 and 9 are associated with higher risks of adverse developmental outcomes, then the determinants of Apgar scores between 7 and 9 may include known risk factors, such as neonatal infections, neonatal respiratory distress, and hypoxic-ischemic encephalopathy, for adverse developmental outcomes.
In our latest study we showed for the first time that babies born at term, with no malformations, and scoring within the normal range of 7 to 9 are strongly associated with neonatal mortality, infections, asphyxia-related complications, hypoglycemia, and respiratory distress and that these associations are substantially stronger with increasing time after birth. [5] Additionally, a decrease in the five-minute Apgar score of 10 to a 10-minute score of ≤9 is associated with a higher risk of neonatal morbidity. Consequently, these results provided insight into our previous findings of increased risks of cerebral palsy, epilepsy, and adverse developmental outcomes in children with Apgar scores of 7, 8, and even 9, compared with an Apgar score of 10.
Current guidelines consider Apgar scores of ≥7 at one and five minutes to be reassuring, however our results provide strong evidence to support the proposition that efforts should be made to reduce the rate of low Apgar scores within the normal range and to strive for an Apgar score of 10 immediately after birth. [6] Furthermore, all newborns should be assigned an Apgar score at 10 minutes, regardless of their score at one and five minutes. This will enable at-risk neonates to be identified and monitored to minimize the risk of adverse outcomes. We should touch on the fact that the Apgar score is prone to interobserver variability. Nevertheless, the Apgar score has been shown to have good internal validity and is still in use all over the world to describe the early neonatal state of babies.
References:
- Razaz N, Boyce WT, Brownell M, et al. Five-minute Apgar score as a marker for developmental vulnerability at 5 years of age. Archives of Disease in Childhood – Fetal and Neonatal Edition 2016;101(2):F114-F20. doi: 10.1136/archdischild-2015-308458
- Razaz N, Tedroff K, Villamor E, et al. Maternal body mass index in early pregnancy and risk of epilepsy in offspring. JAMA Neurology 2017;74(6):668-76. doi: 10.1001/jamaneurol.2016.6130
- Persson M, Razaz N, Tedroff K, et al. Five and 10 minute Apgar scores and risks of cerebral palsy and epilepsy: population based cohort study in Sweden. BMJ 2018;360 doi: 10.1136/bmj.k207
- Razaz N, Cnattingius S, Persson M, et al. 1 and 5-minute Apgar scores and child developmental health at 5 years of age, a population-based cohort study. BMJ Open (In press)
- Razaz N, Cnattingius S, Joseph KS. Association between Apgar scores of 7 to 9 and neonatal mortality and morbidity: a population-based cohort study of term infants in Sweden BMJ 2019
- Newborn AAoPCoFa. The Apgar Score. Pediatrics 2015;136(4):819.