Okay… there’s a lot here and it’s just scratching the surface of everything that happens during these stages. This read isn’t meant to fully educate you on the processes, but to help you expand your awareness of the complexities and miracle new life is.
This post will cover the first 2 stages of human development: prenatal and infancy. I’ll cover processes that take us from conception through brain and body development, and parenting practices relevant to the prenatal stage and infancy stage.
Let’s jump in.
Prenatal
Conception to Birth
Germinal (0 - 2 weeks)
When the zygote forms (sperm + egg = cell, aka zygote) and implants in the uterus (process of fertilization).
Embryonic (3 - 8 weeks)
Development of major organs and body systems through process of cell division. Heartbeat detectable around 6 weeks.
Fetal (9 - 40 weeks)
Maturation on all fronts: physical, neurological, sensory systems. The infant’s ability to survive outside the mother’s womb (aka viability) increases after 24 weeks (or for those of us that better comprehend time by the passing of months rather than weeks… about 6 months).
Neurological Development
There are 7 stages to brain development. (1) Cell birth, (2) cell migration, (3) cell differentiation, (4) cell maturation, (5) synaptogenesis, (6) cell death and pruning, and (7) myelogenesis.
Stage 1: Cell Birth (Neurogenesis)
A process beginning at conception through about month 4 of pregnancy.
→ Neurons
These cells are responsible for (1) communicating signals between the brain and body, (2) processing electrical impulses, or action potential, for decision-making, (3) releasing neurotransmitters like serotonin and dopamine to convert electrical signals into chemical signals, (4) sensory processing of external and internal stimuli, (5) carrying signals from brain and spine to muscles and glands to achieve voluntary and involuntary movement, and (6) synaptic plasticity, which supports learning and memory.
Without neurons (nerve cells), there would be no senses, thoughts, emotions, or movement—no life.
Stage 2: Cell Migration
Cells travel from the ventricular zone (the innermost layer of the developing brain) outward to designated locations in brain for proper neurodevelopment/ wiring brain circuits.
Stage 3: Cell Differentiation
When cells become specialized in their function. Gene expression takes place here, which determines the neuron’s identity and role in the brain.
→ Brain Cell Proliferation: Process in which a small set of precursor cells divide in two, then go through multiple cycles of division. Early cycles are quick to double cells while later cycles are slower. This process occurs 40 days after conception and ceases around 125 days (~1 month thru ~4 months).
Stage 4: Cell Maturation
When cells undergo changes and create new connections between neurons. It’s important for tissue and organ function. Mishaps during this stage can lead to disorders or deficiencies.
Stage 5: Synaptogenesis
The formation of synapses, which are connections between neurons that allow communication and information processing in the brain.
Stage 6: Cell Death & Pruning
The elimination of unnecessary and underperforming cells. It is a process of refinement and efficiency in brain performance.
Stage 7: Myelogenesis (Gliogenesis)
This process begins around month 4 of pregnancy and functions throughout life.
Final step! Myelin is a fatty substance that is produced and wrapped around nerve fibers for protection and signal transfer efficiency. It establishes the brain pathways that guide thoughts, feelings, memories, and behaviors.
→ Glial Cells
The supporting cells in the Central Nervous System (brain and spine) and Peripheral Nervous System (nerves and ganglia). They maintain homeostasis, create protection, and facilitate repair and growth. They are a crucial support to the neuron’s overall function.
Parenting Practices
Positive interactions and the baby’s environment are of the biggest influencers to brain development. When the caregivers facilitate those, it enable the child to feel secure and loved, which enables neural connections to grow stronger and contribute to a healthy brain.
Play soft music and read to baby it the utero, laugh with friends and loved ones, incorporate activities that help you feel content, and lean on your support system.
Infancy
Birth to 12 Months
Birth
Reflexes such as sucking, grasping, and rooting are present. Baby’s sense of balance and motion is active; rocking and movement a means of calming.
Vision is the least developed; only being able to see about 8-12 inches away. Baby’s hearing is well developed and can recognize their mother’s voice and show preference for familiar rhythms (like a lullaby or story heard in utero). Touch is highly developed and essential for soothing, feeding, and bonding. Skin-to-skin contact regulates baby’s heart rate, temperature, and stress.
Baby prefers sweet tastes (breast milk) and dislikes anything bitter or sour. Smell guides feeding and baby can recognize mother’s scent within days. Around 1-2 weeks, infants can differentiate between familiar and unfamiliar people by scent.
2 - 4 Months
Head control improves and baby begins rolling over. Infants can track moving objects and begin distinguishing colors. Depth perception begins developing while infant gains better control of eye movement. Infant responds to sounds and is soothed by familiar voices.
6 Months
Baby can sit with support. Weight doubles since birth. Vision sharpens and infant is capable of recognizing a familiar face at a distance. Infant can distinguish differences in speech sounds from all languages. Solid foods are introduced and infant’s palate expands. Flavor preferences are shaped by repeated flavors.
9 Months
Crawling begins and pincher grasp develops. Infant develops ability to distinguish subtle differences within their native language. Within the first year of life, baby uses touch and mouthing to explore environment and people. Sensitivity varies, with hands, mouth, and face being most receptive.
12 Months
Baby can stand and walk. Weight triples and length increases ~1.5x birth length. Vision is near adult-like clarity. Infant can understand simple words and commands, linking sound to meaning. Utilization of touch is crucial for motor development (grasping, crawling, walking) and emotional security (soothing and bonding). Taste preferences are strongly influenced by early exposure and mother’s diet (via breast milk flavors). Smell is tied to taste, influencing food acceptance and recognition of caregivers.
Neurological Development
Sensory System Development — During the first year of life, baby’s sensory systems (sight, hearing, touch, taste, smell) and body awareness (balance, movement, awareness of the space they take up) are in rapid development.
Reflexes — At the beginning of life, baby operates through Primitive Reflexes, which are automatic and survival-based. Controlled by brain and spinal cord, these include rooting reflex (turn head toward touch on cheek), startle reflex, grasp reflex, and stepping reflex.
As baby’s brain develops (cerebral cortex and motor pathways), Primitive Reflexes fade and are replaced by voluntary motor skills like rolling, sitting, crawling, pulling, etc. Baby explores motor development and takes on Postural Reflexes that aid in balance control.
Early Attachment — Attachment during these years create the foundation to a person’s physiological and emotional regulation. The role of the main caregiver is to be a model for how the child self-regulates.
→ Consistent modeling/soothing = strong attachment = safe environment = more practice of regulation = development of emotional resilience = foundation to future secure relationships.
Object Permanence — Before object permanence, a baby will believe a hidden item ceases to exist. Once developed, baby will understand that the item still exists even if they cannot see, hear, or touch it (teddy bear is hidden under blanket).
This development also aids in Attachment. Before object permanence, baby’s attachment is primarily based on immediate comfort and discomfort rather than emotional-relational attachment. Once baby understands that caregiver continues to exist outside their senses, attachment becomes rooted in closeness to caregiver (baby’s source of safety). Baby will experience separation anxiety when caregiver leaves by crying and reaching.
Parenting Practices
Birth to 12 Months
Post-birth skin to skin contact. To foster secure attachment during this phase, respond to cries with soothing sounds and movements, tending to baby’s needs. Lay baby on stomach for motor development. Nurturing relationships, positive interactions, and meeting essential needs are crucial influences to healthy brain development.
To continue building a strong attachment and trust when baby goes through separation anxiety, be consistent and predictable. Develop a good-bye routine (wave and hug), acknowledge child’s feelings, model calm emotion, and give an attentive and joyful reunion. Start by practicing short-duration absences, showing child you consistently come back.
Related theories: Sensorimotor (Piaget), Attachment (Bowlby), Strange Situation (Ainsworth).