Prenatal Development and Birth

Prenatal Growth

  • Germinal period

    • About half* of all conceptions fail to grow or implant properly and thus do not survive the germinal period. Most of these are grossly abnormal

    • Zygote begins duplication and division within hours of conception

    • Development of the placenta

    • Implantation (10 days after conception)

    • Organism grows rapidly

  • Embryonic period

    • About 20% percent of all embryos are aborted spontaneously, most often because of chromosomal abnormalities

    • The primitive streak becomes the neural tube and later forms the brain and spine of the CNS

    • Head takes shape

    • Facial features form

    • Heart begins to pulsate

    • Extremities develop and webbed fingers + toes separate

  • Fetal period

    • About 5% of all fetuses are aborted spontaneously before viability at 22 weeks or are stillborn (defined as born dead after 22 weeks)

    • Rapid growth with considerable variation

    • 9th week: SRY gene triggers development of sex organs

    • 3rd month: Neurological sex difference begins

    • Brain

      • Experiences rapid growth

      • Follows proximodistal sequence from brainstem to midbrain, to cortex

      • Develops many new neurons and synapses

      • Begins to regulate basic bodily functions as entire CNS becomes responsive

  • Birth

    • About 31 percent of all zygotes grow and survive to become living newborn babies

    • Fetal brain signals the release of hormones to trigger the female’s uterine muscles

    • Labor begins

      • Average duration for firstborn babies - 12 hours

      • Quicker labor for later-born babies

    • Birthing positions vary

      • Sitting, squatting, laying down, water births

      • Culture and personal preference


Problems and Solutions

  • Harmful substances

    • Prenatal teratogens

      • Any agent or condition, including viruses, drugs that can result in birth defects or complications

  • Risk Analysis Factors

    • Discerns which chances are worth taking and how risks are minimized

      • Critical time

      • Dose/frequency of exposure (threshold effect)

      • Innate vulnerability

  • Threshold effect

    • Certain teratogens

  • Innate Vulnerability

    • Some zygotes carry genes that make them vulnerable

    • Male fetuses are more vulnerable to teratogens than female ones

    • Mother’s genes affect the prenatal environment she provides

    • Neural-tube defects are more common in certain ethnic groups


Low Birthweight + Mother

  • Maternal behavior

    • Maternal health and illness

    • Maternal drug use before and during pregnancy

  • Maternal Malnutrition

    • Fathers and others

    • Father attitudes and behaviors

    • Hispanic paradox

  • Father role

    • Father’s attitude

    • His behavior