2 Prenatal Development and Infancy

Development from pregnancy through infancy

Development begins before birth and continues rapidly through infancy. Physical growth, movement, perception, thinking, communication, relationships, and emotion influence one another. For example, greater control of the body can let an infant explore more of the surroundings and learn from people and objects.

Children tend to follow common developmental patterns, but they vary in when and how they acquire particular skills. Developmental progress is not a fixed timetable.

Prenatal development

Pregnancy is usually dated from the first day of the pregnant person's last menstrual period, about two weeks before fertilization. As a result, gestational age is not the same as time since conception.

The prenatal period is commonly described in three stages:

• Germinal stage: During the first two weeks after fertilization, the fertilized egg divides, travels toward the uterus, and typically implants in its lining.

• Embryonic stage: During roughly weeks three through eight after fertilization, the body's basic structures and major organs begin to form. This is a particularly important period for organ development.

• Fetal stage: From about the ninth week after fertilization until birth, the developing organism is called a fetus. Organs and body systems grow and mature. The brain, lungs, and nervous system continue developing late in pregnancy.

The placenta supports the exchange of oxygen and nutrients and carries waste products away from the fetus. Prenatal growth is influenced by inherited characteristics and the prenatal environment. Some infections, substances, and health conditions can affect development, but these influences change risks rather than determine a child's future. Outcomes depend on many interacting factors, and prenatal care can help identify and address health needs.

Timing of birth

The timing of birth is relevant to development. Birth before thirty-seven completed weeks is preterm. The categories for births at or after thirty-seven weeks are:

• Early term: From thirty-seven weeks through thirty-eight weeks and six days.

• Full term: From thirty-nine weeks through forty weeks and six days.

• Late term: From forty-one weeks through forty-one weeks and six days.

• Postterm: Forty-two weeks or later.

These categories reflect meaningful differences in maturity and newborn outcomes.

Birth and newborn care

Labor and birth mark a major physiological transition. Before birth, the placenta performs essential exchange functions. After birth, a newborn must begin breathing air, regulate body temperature, and adjust to feeding outside the uterus.

Newborn reflexes support early survival and interaction. They include sucking, rooting (turning toward a touch near the mouth), grasping, and the startle reflex. Reflexes are automatic; voluntary control develops gradually.

Essential newborn care includes assessing breathing, keeping the baby warm, preventing infection, and supporting feeding. When medically appropriate, skin-to-skin contact soon after birth can support warmth, early interaction, and the start of breastfeeding.

Physical growth and movement

Infancy—from birth through approximately the second year—is a period of rapid physical growth, especially during the first year. Motor development commonly proceeds from control of the head and trunk toward the arms, hands, and fingers. Gross-motor skills use large muscles, as in rolling, sitting, crawling, and walking. Fine-motor skills involve precise movements, such as reaching, grasping, and picking up small objects.

These are broad trends, not a fixed timetable. Some infants use different movement strategies, and not all crawl before walking. Practice, physical maturation, motivation, and the environment all contribute to skill development.

New abilities create opportunities for exploration. An infant who can sit steadily can use both hands to handle a toy; an infant who can move across a room can investigate objects and people in new ways.

Thinking and perception

Infants learn by looking, listening, touching, moving, and interacting. They attend to patterns and familiar people, explore cause and effect, and gradually develop memory and problem-solving abilities. For example, an infant who repeatedly shakes a rattle to make a sound is discovering a relationship between an action and its result.

A central cognitive achievement is object permanence: understanding that people and objects continue to exist when out of sight. This ability develops gradually. An infant may first search for a partly hidden toy and later look for one that is completely hidden.

What an infant does in these situations can depend on memory, attention, and the ability to act, as well as on what the child knows. Observed performance therefore does not reflect knowledge alone.

Communication and language

Communication begins before words. Infants signal needs by crying and also communicate through gaze, facial expressions, gestures, and body movements. Over the first year, many progress from cooing to babbling with repeated consonant-vowel sounds. They increasingly respond to familiar voices and sounds, attend to speech, and use gestures and vocalizations to engage others.

First meaningful words often emerge around the end of the first year, but timing varies. Understanding usually develops alongside spoken language and often gets ahead of it.

Language grows through social exchange. When an infant points or babbles and a caregiver responds by looking, naming, or talking about what has caught the infant's attention, the exchange provides information about communication and the world. These responsive back-and-forth interactions are called serve and return. Talking, singing, reading, and responding to an infant's signals provide everyday opportunities to learn language.

Relationships and emotional development

Attachment is a lasting emotional bond between an infant and a caregiver. It develops through repeated experiences of care and comfort rather than being guaranteed by a single moment. When caregivers respond sensitively and consistently to an infant's signals, the infant can begin to use the caregiver as a source of comfort and security while gradually exploring the surroundings. Infants can form close relationships with more than one familiar, caring person.

Emotional development also changes rapidly. Newborns show basic states of distress and calm; social smiling, laughter, and a wider range of emotional expressions appear as they mature and interact. Infants rely heavily on adults to help manage distress. Over time, predictable soothing and supportive interaction help them begin to regulate their own emotions.

Later in the first year, wariness of unfamiliar people or distress when a caregiver leaves may appear. These responses vary and can occur as infants become more aware of familiar relationships and their surroundings.

Observing development

Developmental milestones describe skills that most children demonstrate by a particular age. They are useful guides, not diagnoses or guarantees. Infants may progress at different rates across motor, language, cognitive, and social-emotional areas.

Caregivers and professionals can observe development across settings and discuss concerns with a health-care provider. Developmental screening with standardized tools is advised at recommended ages and whenever a concern arises.