PRENATAL
DEVELOPMENT
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Chapter 3
PERIODS OF PRENATAL DEVELOPMENT
1. Germinal
2. Embryonic
3. Fetal
THE GERMINAL PERIOD
• Germinal period: The first two weeks after
conception
• Creation of the zygote, continued cell division,
and the attachment of the zygote to the uterine
wall
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THE GERMINAL PERIOD
• Blastocyst: The inner mass of cells that
develops during the germinal period
• These cells later develop into the embryo
• Trophoblast: The outer layer of cells that
develops in the germinal period
• These cells later provide nutrition and support for the
embryo
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FERTILIZATION/PRENATAL PERIOD
1
5
14
28
FIGURE 3.1 - SIGNIFICANT DEVELOPMENTS IN
THE GERMINAL PERIOD
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THE EMBRYONIC PERIOD
The Embryonic Period - Three to eight weeks
after conception
• The rate of cell differentiation intensifies, support
systems for the cells form, and organs appear
• Organogenesis
• Developmental trends
• Cephalocaudal
• Proximodistal
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THE EMBRYONIC PERIOD
• Endoderm: The inner layer of cells, which develops
into digestive and respiratory systems
• Mesoderm: The middle layer of cells, which becomes
the circulatory system, bones, muscles, excretory
system, and reproductive system
• Ectoderm: The outermost layer of cells, which
becomes the nervous system and brain, sensory
receptors and skin parts
• Life Support:
• Amnion
• Umbilical cord
• Placenta
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HUMAN EMBRYOS AND FETUSES
THE PLACENTA AND THE
UMBILICAL CORD
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THE FETAL PERIOD
• The Fetal Period - Begins two months after
conception and lasts for seven months on
average
• Largest prenatal size and weight gains
• Fingers, toes, skin, features, lungs, other
structures, and reflexes all develop to prepare
for birth
• The three trimesters are not the same as the
three prenatal periods
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FIGURE 3.3 - THE THREE TRIMESTERS
OF PRENATAL DEVELOPMENT
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FIGURE 3.3 - THE THREE TRIMESTERS
OF PRENATAL DEVELOPMENT
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FIGURE 3.3 - THE THREE TRIMESTERS
OF PRENATAL DEVELOPMENT
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THE BRAIN
• At birth – 100 billion neurons
• Neural tube: first 18–24 days after conception,
develops out of the ectoderm
• Two birth defects related to a failure of the
neural tube to close:
• Anencephaly
• Spina bifida
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THE BRAIN
• At about the fifth prenatal week neurogenesis
occurs
• Neurogenesis: Generation of new neurons
• Neuronal migration
• Involves cells moving outward from their point of
origin to their appropriate locations and creating the
different levels, structures, and regions of the brain
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INFLUENCES DURING
PRENATAL PERIOD
• Teratogen: Any agent that can potentially cause
a physical birth defect
• The field of study that investigates the causes of birth
defects is called teratology
• Teratogens include drugs, incompatible blood
types, environmental pollutants, infectious
diseases, nutritional deficiencies, maternal
stress, advanced maternal and paternal age, and
environmental pollutants
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INFLUENCES DURING
PRENATAL PERIOD
• The time of exposure, dose, and genetic
susceptibility to a particular teratogen
influence:
• The severity of the damage to an embryo or fetus
• The type of defect
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TERATOGENS AND THE TIMING OF THEIR
EFFECTS ON PRENATAL DEVELOPMENT
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THE EXPECTANT MOTHER’S NUTRITION
AND WEIGHT GAIN
• Nutrition
• Need for protein, iron, vitamin D, calcium, phosphorus,
magnesium increases 50 percent, water is essential
• Weight Gain
• 25 to 35 pounds associated with best reproductive
outcomes
• Inadequate and excessive weight gain may affect baby
birth weight or mother’s health
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RECOMMENDED NUTRIENT INCREASES
FOR EXPECTANT MOTHERS
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EXERCISE DURING PREGNANCY
• Decrease duration and intensity as pregnancy
progresses
• Avoid high-risk activities
• Warm up, stretch, cool down
• Reduce exercise significantly in last four weeks
• Several studies show exercise during pregnancy
not linked to preterm birth
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PRENATAL CARE
• Prenatal care varies enormously in
• Education
• Screening for manageable conditions and treatable
diseases
• Information on risks and choices before, during, and
after pregnancy
• Good prenatal care makes a difference
• Reduces mortality, physical problems later
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PRENATAL CARE
• Other countries outside the U.S.:
• Have lower rate of low-birth-weight infants
• Free or low-cost prenatal and postnatal care
• Enjoy liberal paid maternity leave
• Factors affecting prenatal care in U.S.
• Individual and social characteristics
• Inadequacy of health care system
• Age group differences (adolescents, adults)
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PERCENTAGE OF U.S. WOMEN USING TIMELY
PRENATAL CARE: 1990 TO 2004
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PRESCRIPTION AND
NONPRESCRIPTION DRUGS
• Prescription and nonprescription drugs, may
have effects on the embryo or fetus that the
women never imagined
• Taking the wrong drug at the wrong time is
enough to physically handicap the offspring for
life
• Prescription drugs that can function as
teratogens include antibiotics
• Nonprescription drugs that can be harmful
include diet pills and aspirin
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PSYCHOACTIVE DRUGS
• Psychoactive drugs
• Act on the nervous system to alter states of
consciousness, modify perceptions, and change moods
• Examples include:
• Caffeine
• Alcohol
• Nicotine
• Cocaine
• Methamphetamine
• Marijuana
• Heroin
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INCOMPATIBLE BLOOD TYPES
• Poses risk to prenatal development
• Between mother and father
• Between mother and baby
• Blood groups (A, B, O, AB)
• Rh factor (positive, negative)
• Vaccine within 3 days of birth
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ENVIRONMENTAL HAZARDS
• Father’s exposure to lead, radiation
• X-ray radiation
• Pollutants and toxin wastes
• Fertilizers and pesticides
• Lead-based paints
• Petrochemicals
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MATERNAL DISEASES
• Diseases and infections cross the placenta
barrier
• Rubella (German measles)
• Diabetes
• Sexually transmitted infections
• Syphilis
• Genital herpes
• AIDS
• HIV infection
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OTHER PARENTAL FACTORS
• Maternal diet and nutrition
• Folic acid and iron
• Fish: PCBs and mercury levels
• Maternal age
• Highest risks: adolescents, over 35 years
• Down syndrome
• Emotional states and stress
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OTHER PARENTAL FACTORS
• Paternal factors
• Father’s diet and low vitamin C
• Drug use effects on sperm
• Smoking – effects of second-hand smoke
• Father’s age at conception
• Birth defects - Down syndrome, dwarfism, and Marfan’s
syndrome
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