Final answer:
During infancy, which refers to the first year after birth, infants go through noticeable changes in body image. These include the shedding of vernix and lanugo, rapid size and growth wherein the infant roughly triples in weight and doubles in length by their first birthday, and developmental milestones such as teething and the maturation of sensory organs.
Step-by-step explanation:
Infancy is a phase of rapid physical and developmental changes, and it encompasses the first year of life. A newborn infant has several distinctive physical characteristics right after birth, including wet skin, possibly streaked with blood, and covered with patches of vernix. This coating, along with peeling skin on the wrists, hands, ankles, and feet, and the presence of lanugo (fine, colorless hair), are all common. Newborns also have unique body proportions with relatively wide shoulders and hips and comparatively long arms and legs. The abdomen also tends to protrude slightly.
Regarding size and growth, a full-term newborn typically measures about 51 cm (20 in.) in length and weighs about 3.4 kg (7.5 lb). After the initial loss of weight during the first week, infants enter a period of significant growth, generally tripling their birth weight and doubling their length by their first birthday. This growth is most pronounced in the head and trunk, supporting rapid brain, heart, and lung development.
In terms of development, infants experience considerable advancement in motor, sensory, and cognitive abilities. Although the exact timing of these developments varies, they usually follow a similar sequence. Teething begins roughly around six months, with the emergence of deciduous teeth causing discomfort and fussiness. By the end of the first year, infants typically have grown all of their upper and lower incisors.
Moreover, the fetal development stages from weeks 13-16 are marked by the progression of sensory organs, the accumulation of meconium in the intestines, and the growth of scalp hair as organ development completes and body size increases substantially.