What is the normal birth weight for a full‑term (≥37 weeks gestation) newborn at birth (0 days)?

Normal Birth Weight for Full-Term Newborns

A normal birth weight for a full-term newborn (≥37 weeks gestation) at birth ranges from 2500g to 4000g, with the mean birth weight being approximately 3279g. 1, 2, 3

Weight Classification Standards

The American Academy of Pediatrics and CDC define normal birth weight as 2500-4000g for term infants. 2 This classification is critical because:

• Low birth weight is defined as <2500g 2, 4
• Macrosomia (large birth weight) is defined as >4000g 2
• Birth weights outside this normal range carry significantly increased morbidity and mortality risks 5

Population Variations in Birth Weight

Birth weight varies predictably by several demographic factors:

• White infants average 179g (6.3 oz) heavier than Black infants 3
• Male infants average 123g (4.3 oz) heavier than female infants 3
• Multiparous deliveries produce infants averaging 79g (2.8 oz) heavier than primiparous deliveries 3

Clinical Significance of Birth Weight Thresholds

For term infants, mortality and morbidity increase dramatically when birth weight falls at or below the 3rd percentile for gestational age. 5 Specifically:

• Neonatal death rate increases 10-fold (from 0.03% to 0.3%) 5
• Five-minute Apgar scores ≤3 double in frequency 5
• Umbilical artery pH ≤7.0 doubles in frequency 5
• Rates of intubation at birth, seizures, and sepsis all significantly increase 5

Iron Stores and Birth Weight

Healthy term neonates have approximately 75 mg/kg of iron at birth, translating to ~270mg total body iron for a 3.5kg infant. 1 This iron endowment is critical for:

• Supporting the high oxygen consumption of the neonatal brain (60% of total body oxygen) 1
• Maintaining adequate hemoglobin during the fetal-to-adult hemoglobin switch 1
• Preventing iron deficiency anemia in the first 6 months of life 1

Common Clinical Pitfalls

Do not assume all term infants with "normal" appearance are at low risk—birth weight <2500g or at the 3rd percentile carries substantial mortality risk even at term. 5 Key errors to avoid:

• Relying solely on visual assessment rather than accurate scale measurement within 24 hours of birth 1
• Failing to use calibrated electronic scales with 10g resolution 1
• Overlooking that delayed cord clamping (≥30 seconds) can increase total body iron by 33% (~75mg) and should be standard practice 1
• Underestimating the impact of maternal iron status, gestational diabetes, and smoking on birth weight 1