SAR HP 252 Lecture Notes - Lecture 3: Neural Tube Defect, Spina Bifida, Prenatal Development
2 May 2018
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PRENATAL DEVELOPMENT & INFANCY
Factors affecting pregnancy:
• Important to address before the end of the Germinal Period
• Alcohol
• Proper Vitamins/Nutrients
• Genetics
Heredity Environment Interaction
• Nature v. Nurture
• Impacts of having a genetic blueprint v. standard prenatal care
• Genes give people an inclination for a particular developmental trajectory (path) that is
ultimately realized through environmental circumstances
Stages of Embryonic Development
• The Germinal Period: 0-2 weeks
o Includes: creation of a fertilized egg, cell division, attachment of the zygote
(fertilized egg) to the uterine wall
o 1 week – blastocyst (group of specialized inner cells)
• The Embryonic Period: 2-8 or 10 weeks
o A genetic screening (to identify abnormalities, sex, pertinent genes) is usually not
able to be performed until 14 weeks
o Blastocyst Embryo (after attaching to the uterine wall)
▪ Embryo has 3 Layers: Endoderm (inner), Mesoderm (middle)< Ectoderm
(outer)
▪ Trophoblast - outer layer of cells providing nutrition/support for the
embryo)
o 3 Life-Support Systems (formed during this stage)
▪ Amnion – an envelope that contains clear fluid in which the fetus develops
in
▪ Umbilical Cord – contains two arteries and one vein, all connecting the
baby to the placenta
▪ Placenta – a disk-shaped group of tissues where small blood vessels from
both the mother and baby intertwine but do NOT join
o Organogenesis – the process of organ development around two months of prenatal
development
• The Fetal Period: 10 weeks to 38-42 weeks
o Difficult to determine when a baby is due
o Pre-Term Babies – after 24 weeks – before 38 weeks
▪ Babies born before the completion of the fetal period
Germinal Period
• Fertilization Blastocyst Trophoblast Implantation
• Implantation does not guarantee a successful pregnancy
o ex: an empty egg sac
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find more resources at oneclass.com
Embryonic Period
• Embryo – the new name for the blastocyst after attaching to uterine wall
o Amnion
o Umbilical Cord
o Placenta
o Organogenesis
• Embryo v. Fetus
o Embryo – when organs and parts are developed
o Fetus – when abilities are developed (Fetus = Function)
• Important Embryonic Developments
• Week 3 – Neural Tube (Brain & Spinal Cord)
o Precursors to the nervous system
• 21 Days – Eyes
• 24 Days – Heart Cells
• Week 4 – Urogenital Tract, arm/leg buds, heart chambers, blood vessels
• Weeks 5-8 – Arms/Legs, Face, Intestinal Tract
• Week 8 – fetus will be 1/30th of an ounce and 1inch long
Fetal Period
• Two months - Birth
• Viability – the chance of life outside the womb (23-24 weeks)
• Viability is less likely if the fetus is small/weak
Indicators Before Delivery
• The body (particularly the head) is upside down
• Regular-Term – development of muscle tone (due to lack of room in the uterus resulting
in a scrunched up body)
• Pre-Term – lack of muscle tone (due to room in the uterus resulting in freedom to move
around)
• The membrane is permeable
Timeline
•
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find more resources at oneclass.com
Reproductive Challenges
• Infertility – the inability to conceive a child after 12 months of attempting
• In Vitro Fertilization (IVF) – an egg and sperm are combined in a laboratory and the
resulting fertilized egg is transferred to a woman’s uterus
o Popular method to obtain a pregnancy without sex
o This method often results in multiple births, which can lead to premature births
The Brain
• 100 billion neurons (nerve cells) at birth
• Increases in connectivity and functioning occur from the third trimester – age 2
o The brain is still developing until age 2
• Neural Tube: 18-24 days post conception
o Usually before the mother knows she is pregnant
Neural Tube Defects
• Formed by a layer of cells that “zip up”
• Folic Acid – ensures that the neural tube closes
o A lack of this can lead to Spina Bifida/Anencephaly
• Spina Bifida – when spinal cord material protrudes through the spine
o Can lead to hydrocephaly – water on the brain
• Anencephaly – when the neural tube fails to close at the head
o Can lead to death at birth or shortly after
Prenatal Screening & Diagnostic Tests
• Tests used to determine if a fetus is developing normally
• All involve taking material from the uterus which can threaten the possibility of abortion
o Ultrasound Sonography – when high-frequency sound waves are directed into the
abdomen and the resulting echoes create a visual representation of the fetus’s
inner structures
▪ Used to see structure abnormalities and conducted 7+ weeks into a
pregnancy
o Brain Imagine Techniques (Fetal MRI) – uses a powerful magnet and radio
images to create a detailed image of the internal organs and structures
▪ More detailed than an ultrasound
o Chorionic Villus Sampling – samples the placenta to detect genetic defects and
chromosomal abnormalities
▪ This poses a risk of limb deformity
o Amniocentesis – uses a sample of amniotic fluid (what fetuses are held in) to test
from chromosomal/metabolic disorders
▪ Better performed later than earlier (after 16 weeks is ideal) because the
diagnosis is more accurate
o Maternal Blood Screening – uses blood from the mother to determine risk for
birth defects
▪ ex: if AFP is elevated this can indicate a risk for down syndrome
o Noninvasive Prenatal Diagnosis (NIPD) – safer alternative to CVS test
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Important to address before the end of the germinal period: alcohol, proper vitamins/nutrients, genetics. Heredity environment interaction: nature v. nurture, genes give people an inclination for a particular developmental trajectory (path) that is. Impacts of having a genetic blueprint v. standard prenatal care ultimately realized through environmental circumstances. Germinal period: fertilization blastocyst trophoblast implantation. Implantation does not guarantee a successful pregnancy: ex: an empty egg sac. Fetal period: two months - birth, viability the chance of life outside the womb (23-24 weeks, viability is less likely if the fetus is small/weak. Infertility the inability to conceive a child after 12 months of attempting. The brain: 100 billion neurons (nerve cells) at birth. Increases in connectivity and functioning occur from the third trimester age 2: the brain is still developing until age 2, neural tube: 18-24 days post conception, usually before the mother knows she is pregnant.
