Introduction to Psychology/Child and Adolescent Psychology/Prenatal Environment

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Prenatal development is the development of an organism before its birth.

Stages of Prenatal Development[edit]

  1. Germinal stage – conception to 2 weeks
    • Begins at conception and ends when the zygote implants itself in the mother's uterine lining.
    • Between 8 and 12 days after conception, implantation occurs. This is when the zygote embeds itself in the inner lining of the mother's uterus.
  2. Embryonic stage – 3 to 8 weeks after conception
    • blastocyst differentiates to form three cell layers in the embryo: the ectoderm, mesoderm, and endoderm.
      • The ectoderm is the outer layer of the cell mall, and during the embryonic stage it gives rise to the nervous system, sensory receptors, and outer skin layers.
      • The mesoderm becomes the circulatory system, skeleton, muscles, excretory system, reproductive system, the outer layer of the digestive tract, and the inner layer of the skin.
      • The endoderm will eventually become the respiratory system and the remainder of the digestive system.
    • chronological development following conception
      • 3rd week - vulnerable brain cells and spinal cord form from the neural tube
      • 3rd and 4th week - placenta and umbilical cord form
      • by 4 weeks - eyes begin to form, torso continues to form, heart tissue begins to beat, arm buds appear
      • by 5 weeks - arms are developed and legs buds begin to form
      • during 8th week - organogenesis is complete, signaling the end of the embryonic stage and beginning of the fetal stage
  3. Fetal stage - week 9 to birth (38–40 weeks)
    • chronological development following conception
      • 9 through 12 weeks - first arm and leg movements begin, reflexes appear, sex organs develop.
      • 17 through 20 weeks - mother begins to feel movement, heartbeat can be heard with a stethoscope.
      • by 24 weeks - fat forms and rapid weight gain begins
      • 26 through 28 weeks - lungs are mature enough to allow breathing
      • 28 though 40 weeks - major organ systems are functional and brain develops rapidly.


  • preterm births occur before 37 weeks of gestation
  • low birth weight is less than five and half pounds (two pounds lighter than average)
  • Fetal Alcohol Syndrom (FAS)
    • overall growth deficiency, head and facial malformations, and dysfunction of the central nervous system
  • effects of alcohol use
  • effects of cocaine use
  • effects of cigarette smoking
  • sexually transmitted diseases
  • effects of stress