Prenatal Development

Gametes: Eggs and sperm produced by meiosis, each containing half of the required genetic material, specifically a single set of 23 chromosomes.
Conception: The process where the egg and sperm combine to create a zygote, a single cell that contains all genetic material (i.e., 23 pairs of chromosomes). Development begins at this stage.

Cell Multiplication: Cells undergo multiplication by mitosis.
Formation: Changes into a hollow ball of cells (blastocyst).
Implantation: The blastocyst implants into the uterine wall.
Cell Differentiation: Cells begin to differentiate and specialize into embryonic cells and supportive structures that will nurture the embryo, including:
- Amniotic sac: Protective fluid-filled sac.
- Umbilical cord: Nutritional supply connector.

Chorionic Villi: Finger-like projections that aid in nutrient transfer.
Placenta: Organ that transfers nutrients and waste between mother and fetus.
Yolk Sac: Early source of nutrients.
Uterine Lining: Nourishing lining of the uterus.
Chorionic Cavity and Amnion: Surrounding spaces housing the developing fetus.
Locations: External and internal os, cervix, vaginal canal.

Major Structures Formation: Essential internal and external structures begin forming.
Three Germ Layers Formation:
- Endodermal: Develops into internal organs.
- Ectodermal: Develops nervous system, skin, eyes, and ears.
- Mesodermal: Forms muscles, bones, and the heart.
Brain Development: Major brain development occurs in week 5.
Differentiation of Limbs: Notable differentiation by week 6, where the head comprises 50% of the embryo's mass.

Development Characteristics:
- At birth, the head accounts for about 25% of body mass.
- Facial features, nails, and hair begin to develop.
Brain Organization: By 3 months, brain has differentiated into visual, auditory, and cognitive centers; all adult brain cells are present, but connections are still developing.
Physical Activity: In month 3, notable physical movements like fist formation and toe wiggling occur.
Sensory Development:
- Month 4: Eyes become sensitive to light.
- Month 5: Response to sound increases, including kicking and turning; sleep/activity cycles start to emerge.
Later Development: As pregnancy continues, significant growth occurs in brain, lungs, and fat deposits crucial for breathing and temperature regulation. Also, the fetal immune system starts developing with maternal help in month 8.

Definition: The study of teratogens' effects on prenatal development.
Teratogens: Non-genetic agents responsible for developmental defects; their uptake commonly occurs through maternal blood via the placenta after 3 weeks.

Genetic Sensitivity: Varies by species.
Temporal Sensitivity: Effects depend on the timing of exposure.
Effect Specificity: Specific teratogens affect certain organs:
- Thalidomide: Causes limb defects.
- Rubella: Affects sensory organs and internal organs.
Severity: Varies by exposure level.
Method of Access: Different pathways such as radiation vs. chemicals.
Dosage Effects: Higher dosages can exacerbate effects.

Described across the three periods of prenatal development: ovum, embryo, and fetus, with an emphasis on when defects most commonly occur.
Sensitive periods (indicated by dark shading) reveal when specific organs are most susceptible to teratogenic effects.

Rubella: Leads to low birth weight, cataracts, congenital heart disease, microcephaly.
Herpes: Impacts the CNS (central nervous system).
HIV: Causes facial deformities and failure to soothe.
Zika virus: Linked to microcephaly and other defects.
COVID-19: Associated with double the risk of neurodevelopmental disorders and respiratory distress in newborns.
Syphilis & Gonorrhea: Result in prematurity, spontaneous abortions, and eye infections.
Malnutrition: Can cause spontaneous abortion and low birth weight.
Parental Age: Increased age can lead to conditions like Down's syndrome.
Drugs: Street drugs, caffeine, nicotine, and alcohol significantly impair development.

Graphical representation showing relative frequency of disorders such as Down syndrome and Achondroplasia, correlating with maternal age, indicated as follows:
- Down Syndrome: Likelihood increases with age, particularly in mothers aged 35-39 and beyond (≤24, 25-29, 30-34, 35-39, 40-44, ≥45).

Physical Indicators:
- Small head, epicanthal folds, low nasal bridge, and small eye openings.
- Short nose and flat midface, thin upper lip, smooth philtrum, underdeveloped jaw.

Stage 1: Includes contractions of uterus muscles that stretch, soften, and dilate the cervix while helping the baby move down the birth canal.
Stage 2: The mother actively pushes and delivers the baby, which can occur vaginally or via cesarean section.
Stage 3: The final stage involves the delivery of the placenta.

Infants exhibit the ability to distinguish their mother’s voice from that of a stranger, as evidenced by a study where infants suck a pacifier to hear their mother's voice (DeCasper & Fifer, 1980).
A notable study found that infants whose mothers read "Cat in the Hat" twice daily during the last six weeks of pregnancy preferred hearing it over another story, suggesting that prosody, rather than specific words, was learned (DeCasper & Spence, 1986).

Neurotransmitter Release: The pressure during labor hypothetically affects neurotransmitter release and neuronal wiring in the infant's brain.
Gut Microbiome Exposure: Traveling through the birth canal exposes the infant to microorganisms that assist in establishing their gut microbiome, whereas C-section deliveries may miss this critical exposure.

Graphical representation showing reactive latencies (in milliseconds) between vaginally delivered infants and C-section delivered infants, indicating potential developmental differences.
Data suggests that C-section delivery may influence attention and cognitive outcomes.