Infant

• 1. Introduction

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  An infant arrives wet, streaked with blood, and coated in a white substance called vernix caseosa, a coating thought to act as an antibacterial barrier. Within a minute or two of the first breath, skin that was grayish or dusky blue settles into its normal tone. The word infant literally means unspeaking, a formal synonym for what most people simply call a baby. In medical usage, a neonate is an infant in its first 28 days of life. How does a body this new measure itself against the adult it will become? Why does its skull arrive unfinished, with soft spots that have not yet turned to bone? And how does a being who cannot yet say a single word begin to shape the people around it?

• 2. A Body Out Of Proportion

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  A newborn's head is enormous relative to the face, and large in proportion to the whole body. Where the adult human skull is about one seventh of total body length, the newborn's claims a far greater share. Normal head circumference for a full-term infant runs 33 to 36 centimeters at birth.

  The cranium arrives only partly built. Many regions have not yet been converted to bone, leaving soft spots called fontanels. The two largest are the diamond-shaped anterior fontanel at the top front of the head and the smaller, triangular posterior fontanel at the back. These bones fuse together later in a natural process, and a protein called noggin is responsible for the delay in that fusion.

  The shoulders and hips are wide, the abdomen protrudes slightly, and the arms and legs are relatively long for the rest of the body. During labour and birth, the skull itself changes shape to fit through the birth canal, sometimes producing a misshapen or elongated head. It usually returns to normal on its own within a few days or weeks, though physicians sometimes advise special exercises to assist.

• 3. Measured At Birth

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  In developed countries, the average total body length of a newborn falls between 35.6 and 50.8 centimeters, with premature newborns much smaller. The measurement is taken by laying the baby down and stretching a tape from the top of the head to the bottom of the heel.

  The average birth weight of a full-term newborn is approximately 3.4 kilograms, typically ranging from 2.7 to 4.6 kilograms. Over the first 5 to 7 days, a term neonate's body weight drops by 3 to 7 percent. That loss comes largely from resorbing and urinating the fluid that initially fills the lungs, plus a delay of often a few days before breastfeeding becomes effective.

  After that first week, healthy term neonates should gain 10 to 20 grams per kilogram each day. Whether born premature, full term, late term, or post term, every infant is sorted by the same clock: born before 37 weeks is premature, between 39 and 40 weeks is full term, through 41 weeks is late term, and beyond 42 weeks is post term.

• 4. Skin, Cord, And Curiosities

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  Mongolian spots, peeling skin around the wrists and ankles, a scalp temporarily bruised or swollen, eyes left puffy: a newborn arrives marked in ways that alarm before they reassure. Some newborns carry a fine, downy body hair called lanugo, most noticeable on the back, shoulders, forehead, ears and face of premature infants, and it disappears within a few weeks.

  Hair on the head is its own surprise. Some infants arrive with full heads of it; others, particularly Caucasian infants, may have very fine hair or be bald, and among fair-skinned parents the fine hair may come in blonde even when the parents are not. Color and texture then change with time: red can give way to blond, curly can go straight, thick dark hair can return sparser and lighter.

  The umbilical cord arrives bluish-white and is normally cut after birth, leaving a stub of 1 to 2 inches that dries, shrivels, darkens, and falls off on its own within about 3 weeks, later healing into a belly-button. Inside that cord run three vessels: two arteries carrying blood from the baby to the placenta, and one vein carrying it back. The genitals appear enlarged and reddened, the breasts may swell even in male infants, and some discharge a substance sometimes called witch's milk, all driven by maternal hormones and all temporary.

• 5. The First Conversations

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  An infant cries as a form of basic instinctive communication, signaling hunger, discomfort, overstimulation, boredom, a want, or loneliness. Infants are altricial, fully dependent on a mother or adult caretaker for an extended period, and they arrive with a sucking reflex and an instinctive rooting behavior that seeks out the nipple.

  Language begins long before words. Caregivers are advised to pick up on an infant's facial expressions and mirror them, using exaggerated expressions and melodic, accentuated pronunciation, while avoiding simplified baby talk such as "Did you 'ouch'?" instead of "Did you hurt yourself?". Picking up the baby's babbling and repeating it begins the first simple dialogues.

  Timing matters more than comprehension. Researchers studied mothers' behavior toward 8-month-old infants, then tested those infants' vocabulary at 15 months, and found that a prompt response to babbling led to faster language acquisition. When a parent comments as a baby looks at a ball and babbles, the baby learns that sounds attach to objects. The crucial discovery for the infant is that babbling can influence a parent at all, the beginning of intentional communication. But this only works when parents react positively; trying to divert the infant's attention to something else is detrimental to language development.

• 6. Held And Carried

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  A 2013 study found that infants left in a cradle cried and kicked more and showed an increased heart rate, while those picked up and carried by a walking mother calmed significantly. Being held motionless in the arm produced an intermediate effect, between carrying and being put down. A randomized study back in 1986 had already shown that carrying, as in a baby sling, makes infants more content and makes them cry less.

  Touch carries weight beyond comfort. Experiments with infants up to four months old compared positive touch, such as stroking or cuddling, against negative touch, such as poking, pinching, or tickling. Infants who received positive touch cried less and smiled and vocalized more, while negative touch has been linked with later emotional and behavioral problems, and cultures with more positive physical touching show less physical violence among adults.

  Maternal sensitivity shapes the bond itself. It means attending to the infant's behavioral expressions without misreading them through one's own moods, then responding promptly and appropriately. Infants show an inborn drive to seek closeness to the mother or another primary caregiver, protesting separation by crying and body movements, and a secure attachment grows from empathetic, prompt responses. Children also need far more sleep than adults, up to 18 hours for newborns, a rate that declines with age.

• 7. Attachment And Alarm

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  Attachment theory is primarily an evolutionary and ethological account, in which an infant seeks proximity to a specified attachment figure during alarm or distress for the purpose of survival. Attachment behaviors tend to develop between six months and 3 years, and the bonds an infant forms become the foundation for relationships throughout life. Attachment is not the same as love or affection, though the two often go together.

  Infants attach to adults who are sensitive and responsive and who remain consistent caregivers over time. Parental responses build patterns of attachment, which lead to internal working models that guide a person's feelings, thoughts, and expectations in later relationships. These patterns fall into styles named secure, anxious-ambivalent, anxious-avoidant, all organized, and disorganized, with some more problematic than others. A lack of attachment, or a seriously disrupted capacity for it, could amount to serious disorders.

  Danger registers early. Infants respond to a snake's hiss, the angry voices of adults, the crackle of fire, thunder, and the cries of other infants with a drop in heart rate, blinking eyes, and turning toward the source, all signs of heightened attention believed to be an evolutionary response to threat. A baby's ability to accurately locate sounds is refined during the first year. Beyond the bond with one parent, the quality of the triadic relationship between mother, father, and infant also matters for mental health.

• 8. Fragile Beginnings

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  Infant mortality, the death of an infant in the first year of life, is often expressed as deaths per 1,000 live births, and its major causes include dehydration, infection, congenital malformation, and SIDS. The newborn's physiological systems, including the immune system, are far from fully developed, leaving it open to conditions such as neonatal jaundice, neonatal sepsis, and neonatal meningitis.

  The infant mortality rate is recognized as a very important measure of a country's level of health care, linked to the health of infants, children, and pregnant women, to access to medical care, and to socioeconomic conditions. There is a positive relationship between national wealth and good health. Rich, industrialized countries such as Canada, the United Kingdom, the United States, and Japan spend heavily on sophisticated health care systems and see low infant mortality, while a country like Mexico, spending proportionately less, suffers higher rates.

  The gap appears within nations too. In the United States, the average infant mortality rate is 6.8 per 1,000 live births, but among non-Hispanic black women it reaches 13.63, against 5.76 for non-Hispanic white women. Babyhood is described as a critical period when the foundations of adult personality are laid, a stage that ends only when a baby gains relative independence in moving about and feeding and earns a new name: toddler.