From the Guidelines
The main difference between Small for Gestational Age (SGA) and Appropriate for Gestational Age (AGA) neonates is their birth weight relative to gestational age, with SGA neonates having a birth weight below the 10th percentile for their gestational age, while AGA neonates have a birth weight between the 10th and 90th percentiles, which is considered normal.
Key Differences
- SGA babies may be constitutionally small or growth-restricted due to placental insufficiency, maternal factors (hypertension, malnutrition, substance abuse), fetal factors (genetic disorders, congenital infections), or environmental factors 1.
- These babies face higher risks of perinatal complications including hypoglycemia, hypothermia, polycythemia, and impaired neurodevelopment, and require closer monitoring of blood glucose, temperature regulation, and feeding support 1.
- Long-term, SGA infants may experience catch-up growth but can have increased risks of metabolic disorders in adulthood.
- AGA babies, by contrast, have grown appropriately in utero and generally have lower risks for these complications, requiring standard newborn care rather than the intensified monitoring needed for SGA infants.
Clinical Management
- The distinction between SGA and AGA is important for clinical management as SGA status signals the need for more vigilant care and follow-up.
- According to the most recent guidelines, SGA neonates should be monitored closely for signs of hypoglycemia, hypothermia, and other complications, and receive prompt treatment if necessary 1.
- The use of abdominal circumference (AC) as a diagnostic criterion for fetal growth restriction (FGR) has been supported by evidence, with an AC of less than the 10th percentile having diagnostic accuracy similar to estimated fetal weight (EFW) less than the 10th percentile for the prediction of SGA 1.
Risks and Outcomes
- FGR occurs in up to 10% of pregnancies and is a leading cause of infant morbidity and mortality, with stillbirth rates approximately twice as high in fetuses with weights below the 10th percentile compared to those with normal growth 1.
- Infants with birthweights below the 10th percentile are more likely to have severe acidosis at birth, low 5-minute Apgar scores, and neonatal intensive care unit admissions 1.
- Prematurity further compounds the risk of adverse outcomes in FGR, with a 2- to 5-fold increased rate of perinatal death among preterm FGR fetuses compared to term FGR fetuses 1.