Classification of Newborns by Weight and Gestational Age

Categorization by Birth Weight

• The American Academy of Pediatrics recommends classifying newborns as having low birth weight (less than 2500g), very low birth weight (less than 1500g), or extremely low birth weight (less than 1000g) 4, 5, 6
• Newborns with a birth weight of 2500-4000g are considered to have a normal weight 3
• Macrosomia is defined as a birth weight greater than 4000g 3

Categorization by Gestational Age Percentiles

• The American College of Obstetricians and Gynecologists defines small for gestational age (SGA) as a birth weight below the 10th percentile for gestational age 3
• Adequate for gestational age (AGA) is defined as a birth weight between the 10th and 90th percentiles for gestational age 3
• Large for gestational age (LGA) is defined as a birth weight above the 90th percentile for gestational age 3

Gestational Age Classification

• Preterm birth is defined as less than 37 weeks of gestation 1, 2
• Late preterm birth is defined as 34-36 weeks of gestation 2
• Moderate preterm birth is defined as 32-34 weeks of gestation 1, 2
• Very preterm birth is defined as less than 32 weeks of gestation 1, 2, 5
• Extremely preterm birth is defined as less than 29 weeks of gestation 4, 5

Implications for Neonatal Care

• The American Academy of Pediatrics recommends that newborns with a gestational age of less than 32 weeks or a birth weight of less than 1500g receive critical care 2
• Newborns with a gestational age of 32-34 weeks or a birth weight of 1500-2500g may require special care 1, 2

Evidence for Mortality and Regionalization

• Regionalized care reduces mortality: very low birth weight newborns cared for in lower-level centers have an odds ratio of death of 1.60 (95% CI 1.33-1.92) compared to higher-level centers 4, 5
• Volume matters: centers with less than 100 annual admissions of very low birth weight newborns have an odds ratio of death of 1.19 (95% CI 1.04-1.37) compared to higher-volume centers 5, 6

Special Considerations

• The Society for Maternal-Fetal Medicine and the American College of Obstetricians and Gynecologists recommend using population-based references instead of customized standards to determine fetal weight percentiles 3