An infant or baby is the very young offspring of human
beings. Infant (from the Latin word infans,
meaning 'baby' or 'child'[1])
is a formal or specialised synonym for the common term baby.
The terms may also be used to refer to juveniles of
other organisms. A newborn is, in colloquial use,
an infant who is only hours, days, or up to one month
old. In medical contexts, a newborn or neonate (from
Latin, neonatus, newborn) is an infant in the
first 28 days after birth;[2] the
term applies to premature, full
term, and postmature infants.
Infants born prior to 37 weeks of gestation are called
"premature",[3] those
born between 39 and 40 weeks are "full term", those born
through 41 weeks are "late term", and anything beyond 42
weeks is considered "post term".[4]
Before birth, the offspring is called a fetus.
The term infant is typically applied to very
young children under one year of age; however,
definitions may vary and may include children up to two
years of age. When a human child learns to walk, they
are called a toddler instead.
Physical characteristics
Head
Eight-month-old
infant; as a common feature, eyes are usually large in
relation to the face.
A newborn's head is very large in proportion to the
body, and the cranium is
enormous relative to his or her face. While the adult
human skull is about one seventh of the total body
length, the newborn's is about 1⁄4.
Normal head circumference for a full-term infant is
33–36 cm at birth.[6] At
birth, many regions of the newborn's skull have not yet
been converted to bone, leaving "soft spots" known as fontanels.
The two largest are the diamond-shaped anterior
fontanel, located at the top front portion of the head,
and the smaller triangular-shaped posterior fontanel,
which lies at the back of the head. Later in the child's
life, these bones will fuse together in a natural
process. A protein called noggin is
responsible for the delay in an infant's skull fusion.[7]
During labour and
birth, the infant's skull changes shape to fit through
the birth
canal, sometimes causing the child to be born with a
misshapen or elongated head. It will usually return to
normal on its own within a few days or weeks. Special
exercises sometimes advised by physicians may
assist the process.
Hair
Thin
brown hair of a one-year-old infant girl
Some newborns have a fine, downy body hair called lanugo.
It may be particularly noticeable on the back,
shoulders, forehead, ears and face of premature infants.
Lanugo disappears within a few weeks. Infants may be
born with full heads of hair; others, particularly Caucasian infants,
may have very fine hair or may even be bald. Amongst
fair-skinned parents, this fine hair may be blonde, even
if the parents are not. An infant's hair color and
texture can change: red can give way to blond, curly can
go straight, and thick, dark hair could reappear a lot
sparser and lighter.[citation
needed] The scalp may
also be temporarily bruised or
swollen, especially in hairless newborns, and the area
around the eyes may be puffy.
Length
In developed
countries, the average total body length of a
newborn is 35.6–50.8 cm (14.0–20.0 in), although
premature newborns may be much smaller.
The way to measure a baby's length is to lay the baby
down and stretch a measuring tape from the top of the
head to the bottom of the heel.
Weight
In developed countries, the average birth
weight of a full-term newborn is
approximately 3.4 kg (7+1⁄2 lb),
and is typically in the range of 2.7–4.6 kg
(6.0–10.1 lb).
Over the first 5–7 days following birth, the body weight
of a term neonate decreases by 3–7%,[8] and
is largely a result of the resorption and urination of
the fluid that initially fills the lungs, in addition to
a delay of often a few days before breastfeeding becomes
effective. After the first week, healthy term neonates
should gain 10–20 grams/kg/day.[8]
Immediately after birth, a newborn's skin is often
grayish to dusky blue in color. As soon as the newborn
begins to breathe, usually within a minute or two, the
skin's color reaches its normal tone. Newborns are wet,
covered in streaks of blood, and coated with a white
substance known as vernix
caseosa, which is hypothesised to act as an antibacterial barrier.
The newborn may also have Mongolian
spots, various other birthmarks,
or peeling skin, particularly on the wrists, hands,
ankles, and feet.
The umbilical
cord of a newborn is bluish-white in color. After
birth, the umbilical cord is normally cut, leaving a
1–2 inch stub. The umbilical stub will dry out, shrivel,
darken, and spontaneously fall off within about 3 weeks.
This will later become a belly-button after it heals.
The umbilical cord contains three vessels: two arteries
and one vein. The two arteries carry blood from the baby
to the placenta while one vein carries blood back to the
baby.
Genitals
A newborn's genitals are
enlarged and reddened, with male infants having an
unusually large scrotum.
The breasts may also be enlarged, even in male infants.
This is caused by naturally occurring maternal hormones
and is a temporary condition. Females (and even males)
may actually discharge milk from their nipples
(sometimes called witch's
milk), or a bloody or milky-like substance from the
vagina. In either case, this is considered normal and
will disappear with time.
Infants cry as
a form of basic instinctive communication.[9] A
crying infant may be trying to express a variety of
feelings including hunger, discomfort, overstimulation,
boredom, wanting something, or loneliness.
Infants are altricial and
are fully dependent on their mothers or an adult
caretaker for an extended period of time.[10]Breastfeeding is
the recommended method of feeding by all major infant
health organizations.[11] If
breastfeeding is not possible or desired, bottle feeding
is done with expressed breast-milk or with infant
formula. Infants are born with a sucking reflex
allowing them to extract the milk from the nipples of
the breasts or the nipple of the baby
bottle, as well as an instinctive behavior known as rooting with
which they seek out the nipple. Sometimes a wet
nurse is hired to feed the infant, although this is
rare, especially in developed countries.
Adequate food consumption at an early age is vital for
an infant's development. The foundations of optimum
health, growth, and neurodevelopment across the lifespan
are established in the first
1,000 days of life.[12] From
birth to six months, infants should consume only breast
milk or an unmodified milk substitute. As an infant's
diet matures, finger foods may be introduced as well as
fruit, vegetables and small amounts of meat.[13]
As infants grow, food
supplements can be added. Many parents choose
commercial, ready-made baby
foods to supplement breast milk or formula for the
child, while others adapt their usual meals for the
dietary needs of their child. Whole cow's milk can
be used at one year, but lower-fat milk is not
recommended until the child is two to three years old.
Weaning is the process through which breast milk is
eliminated from the infant's diet through the
introduction of solid foods in exchange for milk.[14] Until
they are toilet-trained, infants in industrialized
countries wear diapers.
The transition from diapers to training pants is an
important transition in the development of an
infant/baby to that of a toddler. Children need more
sleep than adults—up to 18 hours for newborn babies,
with a declining rate as the child ages. Until babies
learn to walk, they are carried in the arms, held in
slings or baby carriers, or transported in baby
carriages or strollers. Most industrialized countries
have laws requiring child
safety seats for babies in motor vehicles.
