Physical Growth and Development in Infants
Overall Physical Growth
● Birth weight & length
● Normal weight range ~ 5lb 8 oz to 8lb 13oz
● Normal length range ~ 19.5 inches
● Babies lose approx. 5% of body weight in first few days
● Normal adjustment to life outside womb- waste elimination, feeding
● Physical proportions
● Head-to-body ratio: head comprises 25% of total length at birth
● Percentiles: 1-100
● Failure to thrive: a child born in normal ranges falls below 20th percentile
● Detection is key to medical intervention
● Weight:
● At 4 months old, weight typically doubles
● At one year, weight has tripled
● By age 2, weight has quadrupled.
● Length:
● Average length at 12 months ~28.5-30.5 inches
● Average length at 24 months ~33.2-35.4 inches (CDC, 2010).
Brain Growth: The First 2 Years
● Growth
● Physical size of brain increases
● At birth, brain is 25% adult weight
● At 2-years-old, 75%
● Neural development
● Most neurons are present at birth, not fully developed
● Transient exuberance: period of prolific dendritic connections
● Myelination: myelin sheath (fatty cells) protects axons, speeds neural
transmissions
● Pruning: unused connections eliminated in favor of much-used
connections
● Prefrontal cortex
● Least-developed portion of brain at birth; substantial growth
Motor Development
● Reflexes are inborn
● Some are necessary for survival
● Rooting reflex, breathing, sucking reflex
Overall Physical Growth
● Birth weight & length
● Normal weight range ~ 5lb 8 oz to 8lb 13oz
● Normal length range ~ 19.5 inches
● Babies lose approx. 5% of body weight in first few days
● Normal adjustment to life outside womb- waste elimination, feeding
● Physical proportions
● Head-to-body ratio: head comprises 25% of total length at birth
● Percentiles: 1-100
● Failure to thrive: a child born in normal ranges falls below 20th percentile
● Detection is key to medical intervention
● Weight:
● At 4 months old, weight typically doubles
● At one year, weight has tripled
● By age 2, weight has quadrupled.
● Length:
● Average length at 12 months ~28.5-30.5 inches
● Average length at 24 months ~33.2-35.4 inches (CDC, 2010).
Brain Growth: The First 2 Years
● Growth
● Physical size of brain increases
● At birth, brain is 25% adult weight
● At 2-years-old, 75%
● Neural development
● Most neurons are present at birth, not fully developed
● Transient exuberance: period of prolific dendritic connections
● Myelination: myelin sheath (fatty cells) protects axons, speeds neural
transmissions
● Pruning: unused connections eliminated in favor of much-used
connections
● Prefrontal cortex
● Least-developed portion of brain at birth; substantial growth
Motor Development
● Reflexes are inborn
● Some are necessary for survival
● Rooting reflex, breathing, sucking reflex
