The Physical Development Stages of Babies

Physical Characteristics of Newborns

• The average newborn weighs 6.5 to 9 pounds. He will lose 5 to 7 percent of birth weight within a few days after birth. The newborn's length is typically 18 to 21 inches. An infant's head is very large in relation to its body, making up one-fourth of its total body length, and measures on average 12.5 to 14.5 inches in circumference. A baby's normal body temperature ranges from 96 to 99 degrees Fahrenheit, and it is often irregular during the first few weeks of life due to immature body systems and little fat beneath the skin.

Motor Development - Birth to 1 Month

• Most of the newborn's motor activities are reflexive in nature. Among the reflexes present at birth are: coughing, gagging, swallowing, yawning, blinking, sucking, and elimination. Other reflexes are easily activated by environmental stimuli. These include: rooting, Moro (startle), grasping, and stepping reflexes. At this stage in development, the baby stays in the fetal position most of the time, especially when asleep. She will keep her hands in fists, not reaching for objects. When in prone (face down) position, she will turn her head from side to side. The infant's pupils should dilate and constrict in response to light. At this point in development, the eyes do not work together and may seem crossed at times.

Physical Characteristics-1 to 4 Months

• Infants at this stage weigh between 8 and 16 pounds on average, with males weighing slightly more than females. Babies gain about one-fourth to one-half pound per week. The typical length at this phase is 20 to 27 inches; growing about 1 inch per month. Head and chest circumference are about the same at this stage, with head circumference increasing by three-fourths inch per month until 2 months, then increasing by five-eighths inch per month until 4 months. This growth rate is important for proper brain development.

Motor Development - 1 to 4 Months

• During this stage, some reflexive behaviors are fading while others are strengthening. For example, stepping and grasping reflexes will dissipate, and rooting and sucking will mature. The infant will grasp with her entire hand, though her strength is insufficient to actually maintain hold on an object. She will begin to hold her hands in an open position during this period. She can raise her head and upper body while in a prone position. She will move her hands and arms more; waving her arms, clasping her hands, and reaching for objects. She begins to roll from front to back. Baby's eyes begin to move together (binocular vision).

Physical Characteristics - 4 to 8 Months

• During this phase, the infant will gain about one pound per month, eventually doubling the original birth weight. The average length of babies at this stage is 27.5 to 29 inches, continuing to increase by one-half inch per month. Head circumference continues to increase, which indicates brain growth. The infant will begin to cut teeth, with the upper and lower incisors appearing first. Signs of teething include swollen gums, increased drooling, and chewing or mouthing of objects. The child's true eye color is established during this stage.

Motor Development - 4 to 8 Months

• At this stage, the infant will reach for objects with both arms at once. She can sit alone without support. She will use her finger and thumb (pincer grasp) to pick things up. She will transfer things from one hand to the other, grasping with the entire hand (Palmer grasp). She can hold her own bottle. She is able to pull herself into a crawling position, can rock back and forth, but in general does not move forward. She can roll over from front to back and back to front. She can lift her head when placed on her back. She likes to be place in a standing position, especially on a person's lap, and will jump in place.

Physical Characteristics and Motor Development - 8 to 12 Months

• The infant's body weight triples from birth to 12 months, averaging 21 pounds. Gains in height are slower than in previous stages, reaching about 1 and one-half times birth length by 12 months. Typically, four upper and four lower incisors come in, as well as two lower molars. The infant will explore new objects by poking with one finger. She will reach with one hand to grasp offered toys. She releases objects by dropping or throwing; is not able to put things down intentionally. Begins to stand alone, holding onto furniture for support. She will creep on her hands and knees, and can crawl up and down stairs. She will begin to walk with adult help, holding onto hands. Some infants may begin to walk on their own toward the end of this stage.