Defining small-for-gestational-age: prescriptive versus descriptive birthweight standards.

Abstract

Descriptive population-based birthweight standards possess low sensitivity in detecting infants with growth impairment. A prescriptive birthweight standard based on a 'healthy' subpopulation without risk factors for intrauterine growth restriction might be superior. We created two birthweight standards based on live born, singleton infants with gestational age 24-42weeks and born in The Netherlands between 2000 and 2007. Inclusion criteria for the prescriptive birthweight standard were restricted to infants without congenital malformations, born to healthy mothers after uncomplicated pregnancies. We defined small-for-gestational-age (SGA) as birthweight <10th percentile and assessed the ability of both standards to predict adverse neonatal outcomes. The prescriptive birthweight standard identified significantly more infants as SGA, up to 38.0% at 29weeks gestation. SGA infants classified according to both standards as well as those classified according to the prescriptive birthweight standard only, were at increased risk of both major and minor adverse neonatal outcomes. The prescriptive birthweight standard was both more sensitive and less specific, with a maximum increase in sensitivity predicting bronchopulmonary dysplasia (+42.6%) and a maximum decrease in specificity predicting intraventricular haemorrhage (-26.9%) in infants aged 28-31weeks. Prescriptive birthweight standards could improve identification of infants born SGA and at risk of adverse neonatal outcomes. • Descriptive birthweight standards possess low sensitivity in detecting growth restricted infants at risk of adverse neonatal outcomes. • Prescriptive standards could improve identification of very preterm small-for-gestational-age (SGA) infants at risk of intraventricular haemorrhage. What is New: • Prescriptive standards identify more preterm and term SGA infants at risk of major adverse neonatal outcomes. • Late preterm and term SGA infants classified according to the prescriptive standard are at increased risk of minor adverse neonatal outcomes with potentially harmful implications.