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Infant - newborn development


Skull of a newborn
Infantile reflexes
Developmental milestones
Moro reflex


Infant development is most often divided into the following areas:


An infant's physical development begins at the head, then moves to other parts of the body. For example, sucking comes before sitting, which comes before walking.

Newborn to 2 months:

Primitive reflexes include:

3 to 4 months:

5 to 6 months:

6 to 9 months:

9 to 12 months:



Crying is a very important way to communicate. By the baby's third day of life, mothers can tell their own baby's cry from that of other babies. By the first month of life, most parents can tell if their baby's cry means hunger, pain, or anger. Crying also causes a nursing mother's milk to letdown (fill the breast).

The amount of crying in the first 3 months varies in a healthy infant, from 1 to 3 hours a day. Infants who cry more than 3 hours a day are often described as having colic. Colic in infants is rarely due to a problem with the body. In most cases, it stops by 4 months of age.

Regardless of the cause, excessive crying needs a medical evaluation. It can cause family stress that can lead to child abuse.

0 to 2 months:

2 to 4 months:

4 to 6 months:

6 to 9 months:

9 to 12 months:


Newborn behavior is based on six states of consciousness:

Healthy babies with a normal nervous system can move smoothly from one state to another. Heart rate, breathing, muscle tone, and body movements are different in each state.

Many bodily functions are not stable in the first months after birth. This is normal and differs from infant to infant. Stress and stimulation can affect:

Periodic breathing, in which breathing starts and stops again, is normal. It is not a sign of sudden infant death syndrome (SIDS). Some infants will vomit or spit up after each feeding, but have nothing physically wrong with them. They continue to gain weight and develop normally.

Other infants grunt and groan while making a bowel movement, but produce soft, blood-free stools, and their growth and feeding are good. This is due to immature abdominal muscles used for pushing and does not need to be treated.

Sleep/wake cycles vary, and do not stabilize until a baby is 3 months old. These cycles occur in random intervals of 30 to 50 minutes at birth. Intervals gradually increase as the infant matures. By age 4 months, most infants will have one 5-hour period of uninterrupted sleep per day.

Breast-fed infants will feed about every 2 hours. Formula-fed infants should be able to go 3 hours between feedings. During periods of rapid growth, they may feed more often.

You do not need to give water to a baby. In fact, it could be dangerous. An infant who is drinking enough will produce 6 to 8 wet diapers in a 24-hour period. Teaching the infant to suck a pacifier or their own thumb provides comfort between feedings.


Safety is very important for infants. Base safety measures on the child's developmental stage. For example, around age 4 to 6 months, the infant may begin to roll over. Therefore, be very careful while the baby is on the changing table.

Consider the following important safety tips:



Onigbanjo MT, Feigelman S. The first year. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 22.

Olsson JM. The newborn. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 21.


Review Date: 2/2/2021  

Reviewed By: Neil K. Kaneshiro, MD, MHA, Clinical Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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