Infant literally meant the one who cannot speak
The word infant comes from Latin īnfāns, a baby or child whose literal meaning is unspeaking. It usually covers the first year of life, sometimes the first two, and gives way to toddler once a child walks. Doctors reserve newborn, or neonate, for the first 28 days after birth.
Birth timing carries its own labels: babies arriving before 37 weeks of gestation are premature, those at 39 to 40 weeks full term, those through 41 weeks late term, and anything past 42 weeks post term. Before birth the offspring is a fetus. British infant schools take pupils aged four to seven, and in law infancy can mean the whole of minority, lasting until the age of majority.
A newborn is built differently from an adult. Its head makes up about a quarter of body length rather than a seventh, with a circumference of 33 to 36 centimetres at full term. Unfused skull areas called fontanels leave soft spots, the largest a diamond at the top front; a protein named noggin delays the fusion. Typical full-term weight in developed countries is about 3.4 kilograms, within a range of roughly 2.7 to 4.6, and length runs from about 36 to 51 centimetres.
In the first five to seven days a term baby loses 3 to 7 percent of its weight, largely by clearing lung fluid, then should gain 10 to 20 grams per kilogram daily. Skin starts greyish-blue and pinks up once breathing begins, usually within a minute or two, under a white coating called vernix caseosa that may resist bacteria. The cord stub, left 1 to 2 inches long, dries and drops off within about three weeks to form the navel. Maternal hormones can briefly enlarge the breasts, even in boys, and produce so-called witch's milk.
Babies are altricial, wholly reliant on carers, and cry to signal hunger, discomfort, boredom or loneliness. Major health bodies recommend breastfeeding, helped by sucking and rooting reflexes, and only breast milk or a substitute until six months. Newborns may sleep up to 18 hours a day.
Source: Infant
