Zygote

Conception to Two Weeks

• Inherited 23 chromosomes, 46 in all from each parent
• Creates a blueprint for every detail of human development
• The child's sex, hair, height, and skin tone

Embryo

From Two Weeks to Eight Weeks 

• Foundations of the brain, spinal cord, and nervous system are established
• Heart begins beating, backbone and muscles are forming, arms, legs, eyes, and ears have begun to show 

Fetus

Eight to Thirty-Eight Weeks

• Everything is present that will be found as an adult
• The fetus sleeps, awakens, exercises, turns its head, and opens and closes its mouth

Neonate

Birth to Two Years

• By ten months, the child imitates word sounds and actions       
• By fourteen months he knows he can make things happen by his actions
• By sixteen months he enjoys games and songs, and eighteen months, his vocab "explodes"

First Trimester

• This time is the most critical in terms of the developing baby's health
• Embryo is most susceptible to negative environmental effects.
• During this stage of development of the central nervous system takes place

Second Trimester

• Organism is capable of movement
• Muscle and bone development begin
• Body growth begins, and fingers and toes develop
• Reflexes, such as sucking and swallowing are developed

Third Trimester

• Growth, especially of the brain
• Fetus can see and hear
• Lungs aren't fully developed until ninth month
• Other systems well developed

Neonatal Development

(Birth to Two Years)

• The newborn is miraculous
• Unique individual with many impressive features
• Baby is born with few reflexes
• Quickly matures and changes
• At birth, average height is 19 1/2 inches
• Physical growth  rapid during first years of life
• Much of early weight gain is fat

Neonatal Development

(Birth to Two Years)

(cont.) 

• Physical growth  rapid during first years of life
• Males slighty heavier than females at birth
• By four months, weight is doubled
• Much of early weight gain is fat
• Fat production slows after nine months

Preschool Development

(Two to Six Years)