Is 2,470 g at 38 Weeks Small for Gestational Age?
Yes, a birth weight of 2,470 g at 38 weeks gestation is small for gestational age (SGA), as this weight falls well below the 10th percentile threshold used to define SGA. 1, 2
Defining the Threshold
- SGA is defined as a birth weight below the 10th percentile for gestational age and sex 1, 2
- At 38 weeks gestation, the 10th percentile birth weight is approximately 2,700-2,800 g, making 2,470 g clearly below this cutoff 2
- The 3rd percentile at 38 weeks corresponds to roughly 2,400-2,500 g, meaning this infant may be approaching or within the severe SGA category (defined as <3rd percentile) 2
Clinical Significance of This Weight
- Infants with birth weight below the 10th percentile have approximately 1.5% stillbirth risk—roughly twice that of normally growing fetuses 2
- When birth weight falls below the 3rd percentile, stillbirth rates increase to approximately 2.5% 2
- SGA infants are at markedly increased risk for severe acidosis at birth, low 5-minute Apgar scores, and NICU admission 2
Immediate Neonatal Concerns
- Short-term complications include hypothermia, hypoglycemia, and polycythemia, all of which require vigilant monitoring in the immediate postnatal period 3, 4
- The risk of perinatal asphyxia is elevated, with intrapartum asphyxia occurring in approximately 50% of SGA infants 5
- Hyperbilirubinemia is more common in SGA newborns and requires close bilirubin monitoring 4
Important Diagnostic Distinction
- The term "small for gestational age (SGA)" should be reserved exclusively for newborns with birth weight <10th percentile, distinguishing it from the prenatal diagnosis of fetal growth restriction (FGR) 2, 6
- Approximately 18-22% of SGA infants are constitutionally small but healthy, not pathologically growth-restricted 1
- Pathological growth restriction is confirmed by abnormal umbilical artery Doppler findings, oligohydramnios, or placental abnormalities 6, 4
Long-Term Implications
- Although most SGA infants (approximately 90%) demonstrate catch-up growth by age 2 years, about 10% remain short and may require growth hormone therapy 3, 7
- SGA infants with rapid catch-up growth and marked weight gain face increased risk of premature adrenarche, early puberty, insulin resistance, obesity, type 2 diabetes, and metabolic syndrome in adulthood 7
- Neurodevelopmental sequelae and cardiovascular disease risk are elevated throughout life 2, 3
Key Pitfall to Avoid
Do not assume all SGA infants are pathologically growth-restricted—differentiate between constitutional smallness and placental insufficiency by reviewing antenatal Doppler studies, placental pathology, and maternal risk factors (hypertension, smoking, hyperthyroidism) 1, 6, 4. This distinction guides the intensity of postnatal monitoring and long-term follow-up.