From the Guidelines
Small for Gestational Age (SGA) and Appropriate for Gestational Age (AGA) neonates are differentiated based on their birthweight percentile for gestational age. The key difference between SGA and AGA neonates lies in their birthweight, with SGA neonates having a birthweight below the 10th percentile for their gestational age, while AGA neonates have a birthweight between the 10th and 90th percentile for their gestational age 1.
Definition and Diagnosis
- SGA is defined as a birthweight less than the 10th percentile for gestational age, which can be due to various factors such as fetal growth restriction (FGR), maternal hypertension, or chromosomal abnormalities 1.
- AGA, on the other hand, refers to neonates with a birthweight between the 10th and 90th percentile for their gestational age, indicating normal fetal growth.
- FGR implies an SGA fetus that has not reached its growth potential and is at risk for adverse sequelae, whereas some SGA fetuses may be constitutionally small but healthy 1.
Clinical Implications
- SGA neonates are at a higher risk of perinatal morbidity and mortality, including stillbirth, severe acidosis, low 5-minute Apgar scores, and neonatal intensive care unit admissions 1.
- AGA neonates, being within the normal birthweight range, generally have a lower risk of these complications.
- The diagnosis of FGR and SGA is based on accurate assessment of gestational age and fetal biometry, with regular surveillance and monitoring of fetal well-being being essential for management 1.
Management and Surveillance
- For SGA fetuses, regular assessment of fetal biometry, amniotic fluid volume, and fetal Doppler studies are crucial for determining fetal well-being and guiding management decisions 1.
- The use of customized growth charts and low-dose aspirin treatment for women with major risk factors for placental insufficiency are also recommended in some guidelines 1.
- The timing of delivery is individualized based on the severity of FGR, gestational age, and fetal well-being, with the goal of balancing maternal, fetal, and neonatal risks 1.
From the Research
Definition and Classification
- Small for Gestational Age (SGA) refers to neonates who are below the 10th percentile for birth weight at a given gestational age 2, 3, 4.
- Appropriate for Gestational Age (AGA) refers to neonates who are between the 25th and 74th percentile for birth weight at a given gestational age 2.
- SGA can be further classified into two categories: constitutionally small and pathologically small, with the latter being associated with intrauterine growth restriction (IUGR) 2, 3.
Risk Factors and Outcomes
- SGA neonates are at increased risk for perinatal mortality and morbidity, including respiratory distress syndrome, intraventricular hemorrhage, and retinopathy of prematurity 5, 6.
- AGA neonates have better outcomes compared to SGA neonates, with lower rates of morbidity and mortality 2, 6.
- SGA neonates who experience rapid catch-up growth are at increased risk of developing metabolic disorders, such as insulin resistance and obesity, later in life 4.
Diagnosis and Screening
- Screening for SGA can be performed using maternal factors, fetal biometry, and biomarkers, with the addition of biomarkers only marginally improving predictive performance 5.
- Ultrasound examination at 36 weeks' gestation is more effective than at 32 weeks in predicting birth of SGA neonates 5.
- Accurate diagnosis of SGA is essential for antenatal and postnatal care, and can be achieved using individually customized fetal growth curves and birth weight percentiles 3.
Follow-up and Recommendations
- SGA neonates require close monitoring and follow-up to detect potential abnormalities and prevent long-term complications 4.
- Treatment with growth hormone may be indicated for SGA children who remain short, and can increase adult height 4.
- Early detection and intervention can improve neurodevelopmental outcomes in SGA infants, particularly those with spontaneous catch-up growth 4.