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Physical Development during Infancy
The average newborn in the United States weighs about 7.5 pounds and is about 20 inches in length. For the first few days of life, infants typically lose about 5 percent of their body weight as they eliminate waste and get used to feeding. This often goes unnoticed by most parents, but can be cause for concern for those who have a smaller infant. This weight loss is temporary, however, and is followed by a rapid period of growth. By the time an infant is 4 months old, it usually doubles in weight and by one year has tripled it birth weight. By age 2, the weight has quadrupled. The average length at one year is about 26-32 inches.
Another dramatic physical change that takes place in the first several years of life is the change in body proportions. The head initially makes up about 50 percent of our entire length when we are developing in the womb. At birth, the head makes up about 25 percent of our length. By age 25 it comprises about 20 percent of our length. Imagine now how difficult it must be to raise one’s head during the first year of life! These deaths often happen during sleep or in the baby’s sleep area.
About 3,500 babies in the United States die suddenly and unexpectedly each year. A thorough investigation is necessary to learn what caused these deaths. Sudden unexpected infant deaths include sudden infant death syndrome (SIDS), accidental suffocation in a sleeping environment, and other deaths from unknown causes. Although the SUID rate has declined since 1990s, significant racial and ethnic differences continue. (40)
Reducing the Risk of SIDS
Health care providers and researchers don’t know the exact causes of Sudden Infant Death Syndrome (SIDS). However, research shows parents and caregivers can take the following actions to help reduce the risk of SIDS and other sleep-related infant deaths:
- Place the baby on his or her back for all sleep times — for naps and at night.
- Use a firm sleep surface, such as a mattress in a safety-approved crib, covered by a fitted sheet.
- Have the baby share the parents’ room, not their bed. The baby should not sleep in an adult bed, on a couch, or on a chair alone, or with anyone else.
- Keep soft objects, such as pillows and loose bedding, out of the baby’s sleep area.
- Parents should not smoke during pregnancy, or allow smoking around the baby. (41)
The Brain in the First Two Years
Some of the most dramatic physical changes that occur during this period is in the brain. At birth, the brain is about 25 percent its adult weight and this is not true for any other part of the body. By age 2, it is at 75 percent its adult weight, at 95 percent by age 6 and at 100 percent by age 7 years.
While most of the brain’s 100 to 200 billion neurons are present at birth, they are not fully mature and during the next several years dendrites or connections between neurons will undergo a period of transient exuberance or temporary dramatic growth. There is a proliferation o