The correct usage of the term “low-birth-weight infant”

To the Editor:

We read with great interest the article by Carroll et al.¹ The study offers new perspectives on the 2 most common causative agents for respiratory tract infections in infants. The results were especially significant as infants with mothers with atopic asthma compared with infants whose mothers did not have asthma were more likely to have rhinovirus versus respiratory syncytial virus infection and among infants with rhinovirus infection, having a mother with atopic asthma was associated with increased infection severity. We believe that these data provide new insights that would be very helpful for both the prognostication and management of infants with these common pathogens in both the Neonatology and Allergy clinics, because premature birth increases the risk of childhood asthma.

However, from a neonatal standpoint, while the cohort of term infants was defined as being 37 weeks or more of gestational age, categorization of term infants with a birth weight of 2250 g or more as “non–low-birth-weight” would be a misclassification.² A “low-birth-weight” infant classically should have been defined as an infant with a birth weight of less than 2500 g, regardless of gestational age at the time of birth. Low birth weight can be a consequence of preterm birth, or due to small size for gestational age (defined as weight for gestation <10th percentile), or both. In addition, depending on the birth weight reference used, a variable but small proportion of low-birth-weight infants are born at term and are not small for gestational age.³ Although the cohort of study does not include any infant with a birth weight between 2250 and 2500 g, the correct use of the terminology would be essential for the design of further studies, because the group of infants falling between 2250 and 2500 g also have an increased risk of childhood asthma.⁴