Prenatal Development

Overview of the Lifespan

  • Prenatal Period: Conception to birth (9-month period)

  • Infancy: First 2 years of life (first month is neonatal or newborn)

  • Childhood: 2 to 10-12 years old (Early: up to age 5-6)

  • Adolescence: 10-12 to 18-22 years old

  • Early Adulthood: Late teens or early 20s to 45 years old

  • Middle Adulthood: 45-60 years old

  • Late Adulthood: 60 years to death

Prenatal Development: Key Terms

  • Perinatal: Environment surrounding birth

  • Prenatal: Before birth

  • Postnatal: After birth

Fertilization: The Moment of Conception

  • Fertilization: Sperm and ovum unit to form a single-celled zygote

  • Zygote contains 46 chromosomes

  • Females born with ~1 million egg cells, ~300,000 remain by puberty

  • Ova mature at puberty, ovulating every ~28 days until menopause

Anatomy of Female Reproductive Organs

  • Fertilization occurs in the Fallopian tube

  • The zygote develops into a blastocyst which undergoes implantation into the uterus

Ovulation

  • Ovulation: Release of an egg (ovum) from an ovary, occurs approximately every 28 days

  • Triggered by spikes in Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH)

Ovulation Predictor Kits

  • Easy-to-use, affordable tests measuring LH levels from urine

  • LH surge predicts ovulation within 24-36 hours

  • Positive result indicates peak fertility

Prenatal Vitamins

  • Contains 400 mcg of folic acid (folate) crucial for normal growth of baby's spine, brain & skull

  • Help reduce risk of neural tube defects (NTD) such as spina bifida and anencephaly

Fertilization Details

  • Adult male produces several hundred million sperm daily; only ~300 million survive to reach the fallopian tube

  • Only one sperm fertilizes the ovum, carrying genetic data to produce a human

Stages of Prenatal Development

  • Lasts ~266 days (9 months)

    • Germinal Stage: 0-2 weeks

    • Embryonic Stage: 3-8 weeks

    • Fetal Stage: 9 weeks-birth

Anatomy of Fetus in Utero

  • Placenta: Temporary organ connecting fetus to uterus

  • Umbilical Cord: Connects fetus to placenta, carrying oxygen and nutrients

  • Amniotic Sac: Thin-walled sac surrounding the fetus

The Germinal Stage

  • Lasts from fertilization to 2 weeks

  • Key events include rapid cell division and the organism becomes increasingly specialized

  • Fertilized egg (blastocyst) travels towards the uterus for implantation

Blastocyst Formation

  • Blastocyst: Hollow ball of ~150 cells, undergoing implantation in the uterine wall

  • Only 10-20% of fertilized ova complete implantation and continue to develop

The Embryonic Stage (3-8 weeks)

  • Develops the amnion, umbilical cord, and placenta

  • Organogenesis: Process of organ formation

Primary Layers of the Embryo

  • Endoderm: Inner layer (digestive & respiratory systems)

  • Mesoderm: Middle layer (circulatory system, bones, muscles)

  • Ectoderm: Outermost layer (nervous system, sensory receptors)

The Fetal Stage (9 weeks to Birth)

  • Embryo transitions to fetus

  • Organs continue to grow and function

  • The fetus becomes progressively active

Fetal Growth and Changes

  • Significant changes in body proportions, growth in weight and length until 40 weeks

  • Example: weight increases from 4 ounces at 4 months to approximately 3 lbs at 7 months

Prenatal Development Timeline

  • Organogenesis follows stages of development, with specific weeks indicating vulnerabilities to teratogens

Hazards to Prenatal Development

Teratogens

  • Agents that can harm a developing fetus (e.g., drugs, diseases)

  • Dose: Greater exposure = greater effect

  • Genetic Susceptibility: Varies between mother and fetus

  • Time of Exposure: Most effects during critical periods of rapid development

Mother's Age

  • Risks associated with advanced maternal age (e.g., premature birth, chromosomal disorders)

Mother’s Health

  • Health conditions such as Rubella can dramatically affect fetal development

  • STDs can lead to serious complications

Mother's Drug Use

  • Prescription and illegal drugs can have severe effects on fetal health

    • Example: Cocaine restricts blood flow to the fetus

Mother's Use of Alcohol

  • Alcohol, regardless of amount, poses risks including Fetal Alcohol Syndrome (FAS), which leads to developmental challenges

  • Vulnerabilities vary by timing of exposure during pregnancy

Prenatal Genetic Testing

Non-Invasive Prenatal Testing (NIPT)

  • Involves first-trimester testing (nuchal translucency and blood tests)

  • Second-trimester tests such as the Quad Serum Screen check levels of specific substances

  • Harmony Prenatal Test: Highly accurate screening for common chromosomal conditions