Prenatal Development and Birth
[Chapter 3]
Chapter Overview
I.
II.
III.
IV.
V.
VI.
The Periods of Prenatal Development
Maternal Conditions and Prenatal Development
Teratogens: Environmental Sources of Birth
Defects
Birth
The Newborn’s Condition
Beginning the Parent-Child Relationship
I. Periods of Pregnancy & Prenatal
Development
 Periods of Pregnancy:
 First Trimester (Conception – 3 months)
 Second Trimester (3 – 6 months)
 Third Trimester (6 – 9 months)
 Birth (~38 weeks)
 Periods of Prenatal Development:
 Germinal Period (conception – 2 weeks)
 Embryonic Period (~2nd week – 8th week)
 Fetal Period (9th week – birth)
The Periods of Prenatal Development
Germinal
(conception – 8-10 days)
Embryonic
(~2nd - 8th week)
Fetal
It has been estimated that 25% of all
pregnancies end before the woman
even knows she is pregnant!
(9th week - birth)
Germinal Period
 Begins at conception
 Lasts until the zygote enters the uterus and becomes
implanted (about 8 to 10 days after conception)
 Organism has grown from a single cell to hundreds
of cells
Embryonic Period
 Begins at implantation (i.e., when the organism
attaches to the uterus)
 Lasts until the end of the 8th week
 All major organs have taken primitive shape
 Sexual differentiation has begun
 The placenta allows the exchange of nutrients and
waste products between the mother and the embryo.
The Embryo
A few important things about the embryo
phase:
 Embryo is very vulnerable during this time.
 Timing of nervous system development is totally
critical.
Prenatal Development
Fetal Period
 Begins at the 9th week
 Lasts until birth
 The fetus dramatically grows in weight and length.
 The brain and all organ systems increase in
complexity.
 By 15 weeks the fetus exhibits all movements
observable at birth.
Fetal Period
 Basic sensory capacities developing
 Example: sensing motion, light, sound
 Environmental influences from outside and inside the
mother can affect fetal development.
 Example: mother’s diet and illnesses
Fetus at 16 Weeks
The growth of the lower part of the fetal body
accelerates. The fetus will kick, which the mother will
feel as a “flutter.”
Fetal Learning
At 32 weeks’
gestation, the fetus
decreases responses
to repeated or
continued
stimulation, a simple
form of learning
called
habituation
Fetal Learning
Newborn infants have been
shown to recognize rhymes
and stories presented before
birth
Newborns also prefer
smells, tastes, and
sound patterns that are
familiar because
of prenatal exposure
2nd
Tri
Zygote
1
2
Embryonic period (wks)
3
4
5
6
7
Fetal Period (wks)
8
9
16
32
Central nervous system
Heart
Arms
Eyes
Legs
Ears
Teeth
Period of structural
dev
Period of functional
dev
Palate
External genitalia
38
Critical Periods in Prenatal Development
Third trimester
begins
About 16.5-18
inches long,
weighs 4 to 5
pounds
Age of
Viability
32 weeks
About 14-17
inches long,
weighs 2.5
to 3 pounds
19 inches
long, weighs 6
pounds
About 11-14
inches long,
weighs 1 to
1.5 pounds
About 10-12
inches long,
weighs 1/2
to 1 pound
First trimester
begins
Less than
1/10th of an
inch long
Less than
1 inch long
About 5.5
inches long,
weighs about
4 ounces
About 3 inches
long, weighs
about 1 ounce
Second trimester begins
Video clip of early fetal development
 http://www.pbs.org/wgbh/nova/miracle/program.html
[ For you to watch in your own time, if you’re interested… ]
II. Maternal Conditions and Prenatal
Development
 Two influences affecting prenatal development:
1. Mother’s attitude towards her pregnancy or stress
during the pregnancy
2. Mother’s nutrition
Maternal Stress
 Some level of stress during pregnancy is to be expected, is
normal and healthy
 However, high levels of stress lead to secretion of stress
hormones (like cortisol) and the fetal exposure to these
hormones can affect development
 Prenatal exposure to stress hormones has been found to be
associated with:
 Low birth weight
 Premature delivery
 Increased aggression during toddler years
Influences of Mother’s Nutrition
 A mother’s nutrition is an important factor in fetal
development.
 Recommended food intake:
– consume enough calories in a well-balanced diet
– increase intake of folic acid, calcium, and iron.
 Effects of extreme undernourishment and malnutrition:
 Low birth weight, premature birth, abnormalities, later
cognitive deficits, and death
 Lesser degrees also increase risk, although effects can be
difficult to isolate
 Overnourishment also a problem!
III. Teratogens: Environmental Sources of
Birth Defects
 Teratogens:
Environmental agents that cause deviations from normal
development and can lead to abnormalities or death.
Teratogens
Six general principles apply to all teratogens:
1.
2.
3.
4.
5.
6.
The susceptibility of the organism depends on its developmental
stage.
A teratogen’s effects are likely to be specific to a particular organ.
Individuals vary in their susceptibility to teratogens.
The mother’s physiological state influences susceptibility.
The greater the concentration of a teratogenic agent, the greater the
risk.
Teratogens that have little or no effect on the mother can seriously
affect the developing organism
Teratogens
• Common Teratogens:
– Drugs
– Including prescription drugs, caffeine, tobacco, alcohol,
marijuana, cocaine, heroin, and methadone
– Infections
– Including rubella and HIV
– Rh Incompatibility
– Radiation or pollution at high levels
• Effects can vary considerably.
Teratogens continued…
 General statements about teratogens
• Teratogenic effects occur mainly during
critical or sensitive periods
• Teratogenic effects can be time specific
• Many teratogens have relatively specific
effects
• Teratogenic effects are often complex
Thalidomide
Teratogens - Cigarettes
 Maternal smoking contributes to:
 Low birth weight
 Decreased placental blood vessel size
 Meaning decreased nutrient transfer between mother and
fetus
 13% of pregnant women smoke
 Hazards of secondhand smoke
Teratogens - Alcohol
 Drinking can cause fetal alcohol
syndrome (FAS)
 the leading cause of mental retardation
in Western Hemisphere
 Effects vary from minimal behavioral
challenges to severe physical and mental
retardation
 Timing, dose, and length of drinking
affect FAS in different ways
 It is still very challenging to tell how
alcohol changes infant development
Teratogens - Illegal Drugs
 There is minimal evidence about the effects of illicit
drugs on fetal development
 Illegal drug use tends to be co-morbid with other risk
factors
 Marijuana – some evidence of premature and low birth
weight
 Heroin and Methadone – tend to be born addicted with
serious consequences throughout life
Spotlight: Cocaine
 Cocaine is an interesting illegal drug, with a lot of research
 Elizabeth Cox has worked with human infants born to cocaine-
using mothers
 Showed that these infants cry differently, more often, and more “noxiously” than
infants born to non-cocaine-using mothers
 Mothers were more likely to report the babies cries as harsher and less appealing than
the cries of babies whose mothers did not use cocaine
 What might these differences mean?
IV. Birth
 A life changing transition for parents and baby
 Options
 Hospital with doctor (92%) or midwife (7%)
 Cesarean delivery rate ~33%
 Natural, medication, hypnosis
 Birthing center (usually midwife)
 Home (assisted or unassisted)
Labor
 Normally begins approximately 266 days (38 weeks)
after conception
 Proceeds through three stages
1. Uterine contractions cause the cervix to dilate
2. The baby is pushed through birth canal
3. The baby is delivered and the afterbirth is delivered
Birth: Cultural Variations
 Childbirth Experiences:
 Be assisted by a physician or midwife in a hospital
 Be assisted by a midwife and/or others at home
 Unassisted birth
 !Kung, Bajura(Nepal)
 Relatively rare
Childbirth in the United States
 99% of babies are born in hospitals
 Most concerns centered around:
 How to safely deal with pain
 Medication
 Precautions to ensure the health of both mother and baby
 Medical interventions
 Alternative Approaches
The Baby’s Experience of Birth
 A stressful experience
 Surge of stress hormones
 May contribute to initiating birth
 Necessary for lungs to function properly
 Increase metabolic rate
 Induces state of alertness
V.
The Newborn’s Condition
 Assessing the Baby’s Vitality
• The Apgar Scale
 Physical condition
• Brazelton Neonatal Assessment Scale
 Behavioral/neurological condition
Primary Goal:
 Screen for infants at risk
Secondary Goal:
 Predict aspects of future development
Physical Condition
• The Apgar Scale
– Assesses physical condition
– Factors rated:
– Heart rate
– Respiratory effort
– Muscle tone
– Reflex responsivity
– Color
– A low score requires immediate medical attention
Apgar Score
A ppearance (skin color)
P ulse
G rimace (reflexes)
A ctivity (muscle activity)
R espiration (breathing)
1 & 5 minutes after birth
Apgar Scale
Score
Body Color
Heartbeat
Reflex
Irritability
Muscle Tone
Respiratory
Effort
0
1
2
Blue, pale
body
Body pink,
extremities blue
Pink all over
Absent
Slow – less than 100 Fast – 100 to 140
beats per minute
beats per minute
No response
Some motion
Coughing,
sneezing, crying
Limp and
flaccid
Inactive, weak,
some flexion of
extremities
Good flexion,
active motion,
strong response
Breathing for
no more than
1 min.
Irregular and slow
Breathing good
with normal crying
Behavioral Condition
 Brazelton Neonatal Assessment Scale
 Assesses subtle aspects behavior
 Includes tests of:
– Reflexes
– Motor capacities
– Muscle tone
– Responsiveness to objects and people
– Control of own behavior
Problems and Complications
 Prematurity
 Birth before the 37th week
 Immature lungs, digestive, or
immune systems
 Low Birth Weight
 Below 5 pounds, 8 ounces (2500
grams)
 Intrauterine growth restrictions
 Developmental Complications!
 Delays and disorders in intellectual
and language development,
attention, and neurological
functioning
VI. Beginning the Parent-Child
Relationship
 The Baby’s Appearance
 Can significantly influence the parents’
response to the baby
 Example: “babyness” (“cuteness”)
The Baby’s Appearance
Baby vs. Adult Graycie 
Social Expectations
 Parental expectations can influence the child’s environment
 Cultural factors are involved in these expectations
 Example: the baby’s sex