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Life Span Development
Prenatal Development and Birth – Chapter 4
June 15, 2004
Class #3
The First Trimester
 Pregnancy is the process referring to the gestation
period of a human being
 A pregnancy is initiated when a fertile sperm from
a male bonds with a fertile egg from a female
 The period of pregnancy (from the woman's last
menstrual cycle to the birth of the child) usually is
40 weeks
 This 40 weeks is divided into three subperiods,
known as "trimesters“
 The first thirteen weeks of pregnancy are referred
to as the "first trimester"
Development of the Embryo and Fetus
 Obstetricians count "weeks of pregnancy"
from the first day of a woman's last
menstrual cycle because there is often no
way to determine exactly when conception
occurred
 Embryologists, however, typically describe
the developing embryo or fetus by the
number of weeks since conception
From Zygote to Newborn
 Germinal period—first 14 days
 Embryonic period—3rd through 8th
weeks
 Fetal period—9th week through birth
Germinal: The First 14 Days
• Zygote divides and keep dividing (at least
though 3rd doubling they are the same)
• At this stage (8 cells) differentiation
begins
- early “stem” cells take on distinct
characteristics
- they gravitate to locations, foreshadowing
the type of cells they will become
Germinal: The First 14 Days
• At about a week after conception the
multiplying cells separate into two masses
- first task of out cells to achieve
implantation— embed themselves into the
nuturant environment of the uterus
• 60% of all natural conceptions fail to
implant; 70% of in vitro procedures fail to
implant
Development of the Embryo and Fetus
 The zygote’s outer part attaches to the
uterine wall forming the placenta
 The inner cells are referred to as the embryo
 By nine weeks, the embryo clearly looks
human and is now a fetus
Role of the Placenta
 The placenta carries nourishment and
oxygen from the mother to the fetus and at
the same time screens out many potentially
harmful substances
– Unfortunately some get through…
Fetal Alcohol Syndrome (FAS)
 FAS is a lifelong yet completely preventable set of
physical, mental and neurobehavioral birth defects
associated with alcohol consumption during
pregnancy
– Alcohol enters the mother’s and the fetus’ bloodstream
 FAS is the leading known cause of mental
retardation and birth defects
– Small disproportioned head and lifelong brain
abnormalities
How does a mother’s drinking affect
her unborn child?
 Facts:
– Through the blood vessels in the placenta, the
mother’s blood supplies the developing baby
with nourishment and oxygen
– If the mother drinks alcohol, the alcohol enters
her blood stream and then, through the
placenta, enters the blood supply of the
growing baby
 So, when a pregnant woman drinks alcohol, so
does her baby
– Alcohol is a teratogen, a substance known to
be toxic to human development
Fetal Alcohol Syndrome (FAS)
 Prenatal alcohol exposure does not always result
in FAS—although there is no known safe level of
alcohol consumption during pregnancy
 Most individuals affected by alcohol exposure
before birth do not have the characteristic facial
abnormalities and growth retardation identified
with FAS, yet they have brain and other
impairments that are just as significant
Sad facts…
 In addition to mental retardation, individuals with
FAS may have other neurological deficits such as
poor motor skills and hand-eye coordination
 They may also have a complex pattern of
behavioral and learning problems, including
difficulties with memory, attention and judgment.
 As many as 12,000 infants are born each year
with FAS
What if I am pregnant and have been
drinking?
 If you consumed alcohol before you knew
you were pregnant, stop drinking now!
– Abstaining from alcohol for the remainder of
your pregnancy can have a beneficial effect
even on functions that might have been affected
by earlier drinking
– The sooner you stop drinking, the better the
chance of having a healthy baby
Smoking cigarettes during pregnancy
(US Dept. of Heath and Human Services, 2001)
 The rate of smoking during pregnancy dropped 33 percent
between 1990 and 1999, so that in 1999 just over 12
percent of all women reported smoking during their
pregnancies, according to a new report from the Centers
for Disease Control and Prevention
– The greatest success in reducing smoking was for
women in their late twenties and early thirties, where
there was over a 40 percent drop since 1990
– Teenagers were more likely than women of any
other age to smoke while pregnant
 After experiencing a dramatic 20-percent decline in
the first part of the decade, smoking rates among
pregnant teenagers–unlike women of all other ages-increased by 5 percent from 1994 to 1999
 The highest rate in 1999 (19 percent) was for women
18-19 years of age
Smoking during pregnancy is related
to violent crimes…
 Brennan, Grekin, & Mednick (1999)
– Subjects were a birth cohort of 4169 males born
between September 1959 and December 1961
in Copenhagen, Denmark
– During the third trimester of pregnancy, mothers
self-reported the number of cigarettes smoked
daily
– When the male offspring were 34 years of age,
their arrest histories were checked in the Danish
National Criminal Register
Brennan, Grekin, & Mednick (1999)
 Found the following data relating smoking during
pregnancy to offsprings’ arrest rate for violent
crimes:
–
–
–
–
–
Mother did not smoke…8%
Mother smoked 1-2 cigarettes per day…9%
Mother smoked 3-10 cigarettes per day…11%%
Mother smoked 10-20 cigarettes per day…15%
Mother smoked > 20 cigarettes/day…18%
 What do you think of these numbers???
Embryo: From the Third to the Eighth Week
 First sign of human structure: thin line
down the middle (22 days) that becomes
the neural tube, which eventually forms
the central nervous system, including brain
and spinal column
– fourth week
 head begins to take shape
 heart begins with a miniscule blood vessel that
begins to pulsate
Embryo: From the Third to the Eighth Week
– fifth week
 arm and leg buds appear
 tail-like appendage extends from the spine
– eighth week
 embryo weighs 1 gram and is 1 inch long
 head more rounded; face formed
 all basic organs and body parts (but for sex) present
– 20% of all embryos spontaneously abort now
Fetus
 Called a fetus from 9th week on
Third Month
• Sex organs take shape (Y cell sends
signal to male sex organs; for females,
no signal occurs)
- genital organs fully shaped by 12th week
• All body parts present
• Fetus can move every part of body
• Fetus weighs 3 ounces and is 3 inches
long
First Trimester:
For the Mom
 There are a wide variety of changes that a woman can
experience
 These physical changes can also cause emotional
reactions
 Sometimes women during the first trimester notice an
energy boost and overwhelming happiness; other women
complain that they are fatigued and emotionally unstable; it
is also possible for women to not even be aware of drastic
fluctuations in their bodies and emotions
 Many women worry that these changes during the first
trimester may adversely affect the growth of the fetus, but
in most cases they do not threaten the well-being of the
fetus
First Trimester:
For the Mom
 Some pregnant women notice aches and pains
 Common complaints are back pains, joint aches,
and leg cramps
 It is essential that the woman rests often in order
to alleviate these aches
 Almost all women notice that they are more tired
than usual during the first trimester
 This feeling of fatigue sometimes remains for the
duration of the pregnancy, although most women
feel noticeably stronger by the third trimester
“Morning Sickness”
 Another problem that affects the mother during early
pregnancy is nausea
 This is a very common problem as it affects almost threefourths of all pregnant women
 Most doctors think that "morning sickness" is caused by the
overproduction of hormones (mostly estrogen) that occurs
during the early pregnancy
 These estrogen hormones then circulate throughout the
bloodstream and affect the body
 Some doctors think that this excess of hormones causes
the stomach to digest food more slowly, which results in the
nausea and the vomiting
 Stress and fatigue may also play a part in causing nausea
and vomiting
Common Complications During
The First Trimester
 Serious complications that can harm either the
mother or the baby occur in about a fifth of all
pregnancies
 There are other common complications that may
cause alarm in the mother, but that typically do not
impact the success of the pregnancy
– For example:
 Vaginal bleeding occurs in about 25% of
pregnancies
 Most cases this is not serious
A very risky time…
 It is estimated that 10 percent of all
recognized pregnancies spontaneously
abort during the first trimester
 The actual number of miscarriages is much
higher
 Perhaps fifty percent of all conceptions
spontaneously result in miscarriage before
the woman even knows that she is pregnant
Second Trimester:
Middle Three Months
 The second trimester of pregnancy encompasses
weeks 14 through 27…
– In the fetus:





Growth continues quickly from now until birth
Organs such as the heart and kidneys develop further
Eyebrows and fingernails form
The skin is wrinkled and covered with fine hair
periods of activity and quiet occur as the fetus moves, kicks,
sleeps, and wakes
 By the end of the second trimester, the fetus is about 11 to 14
inches long and weighs about 2 to 2 1/2 pounds
 It can swallow, hear, and urinate
Middle Three Months:
Preparing to Survive
• Heartbeat stronger
• Digestive and excretory systems
develop more fully
• Impressive brain growth (6X in size
and responsive)
- new neurons develop (neurogenesis)
- synapses—connections between neurons
(synaptogenesis)
Middle Three Months:
Preparing to Survive
• Age of viability—age at which
preterm baby can possibly survive
(22 weeks)
- 26 weeks survival rate about 50%
. brain maturation critical to viability
. weight critical to viability
- 28 weeks survival rate about 95%
Second Trimester:
For the Mom
 During the second trimester, continuing growth
and development in mother and fetus cause many
changes to occur:
– Women may notice the following:
 Their abdomen begins to swell. By the end of the second
trimester, the uterus is near the rib cage.
 The skin on the abdomen and breasts stretches. Stretch marks
may be visible.
 Movements made by the fetus. Known as quickening, this often
occurs sometime around weeks 16 to 20.
 A dark line forming from the navel down to the middle of the
abdomen
 Brown, uneven marks on the face or other changes in skin
pigment
 Darkening of the area around the nipples
No more morning sickness…
 Often, the second trimester delivers a welcome energy
boost to women and an end to morning sickness. It may
also bring:
–
–
–
–
–
–
nasal congestion and occasional nose bleeds
whitish vaginal discharge
less of a need to urinate often
constipation
increase in appetite
Braxton Hicks contractions in which the uterus becomes hard and
tight and then relaxes
– leg cramps
– backache
– fatigue
Miscarriage is now at a much
lower risk…
 Miscarriage in low-risk pregnancies is rare
at this time, but women sometimes have
other problems in the second trimester,
including:
– High blood pressure
– Sugar in the urine. This may be a sign of
gestational diabetes, a form of diabetes
associated with pregnancy
– Iron-deficiency anemia
Final Three Months—
Viability to Full Term
 The third trimester of pregnancy generally
spans weeks 28 through 40…
• Maturation of the respiratory and
cardiovascular systems
- critical difference
• Gains weight—4.5 lbs. in last 10
weeks
Third Trimester
 As the fetus gets bigger, it has less room to kick
and stretch, so the movements felt by the mother
may decrease
 Fine body hair disappears
 Most bones harden, but bones of the head stay
soft and flexible for birth
 As the time for birth approaches, the fetus usually
moves down into the pelvis and settles into a good
position
 At 40 weeks, the fetus is considered full term. It is
about 20 inches long and weighs 6 to 9 pounds
Risk Reduction
 Despite complexity, most babies are born
healthy
 Most hazards are avoidable
 Teratology—study of birth defects
– teratogens—broad range of substances that
can cause environmental insults that may
cause prenatal abnormalities or later learning
abilities
Determining Risk
 Risk analysis—weighing of factors that
affect likelihood of teratogen causing harm
Timing of Exposure
• Critical period—in prenatal
development, the time when a
particular organ or other body part is
most susceptible to teratogenic
damage
- entire embryonic period is critical
Amount of Exposure
 Dose and/or frequency
 Threshold effect—teratogen relatively
harmless until exposure reaches a
certain level
Amount of Exposure
• Interaction effect—risk of harm
increases if exposure to teratogen
occurs at the same time as exposure
to another teratogen or risk
Genetic Vulnerability
• Genetic susceptibilities: product of
genes combined with stress
• Folic-acid deficiency may cause
neural- tube defects
- occurs most commonly in certain ethnic
groups and less often in others
• Males are more genetically vulnerable
Specific Teratogens
 No way to predict risk on an individual basis
 Research has shown possible effects of most
common and damaging teratogens
 AIDS and alcohol extremely damaging
– pregnant women with AIDS transmit it to
their newborns; high doses of alcohol cause
FAS; alcohol + drug use increase risk to
developing organism
Low Birthweight
 Low Birthweight (LBW)
– less than 5 1/2 lbs.
 grows too slowly or weighs less than normal
 more common than 10 years ago
 second most common cause of neonatal death
 Preterm
– birth occurs 3 or more weeks before
standard 38 weeks
Low Birthweight
 Small for Gestational Age (SGA)
– maternal illness
– maternal behavior
 cigarette smoking (25% of SGA births)
– maternal malnutrition
 poorly nourished before and during pregnancy
 underweight, undereating, and smoking tend to
occur together
Low Birthweight
 Factors that affect normal prenatal
growth
– quality of medical care, education, social
support, and cultural practices
Third Trimester:
For the Mom
 Women may notice the following:
– Movements of the fetus can be felt more strongly
– Abdominal pain that may or may not be true labor pains
– Shortness of breath because the uterus is pushing
against the diaphragm. The diaphragm is a flat, strong
muscle that aids in breathing. Towards the end of the
third trimester, the baby may drop down into a lower
position. This will make it easier for the mother to
breathe
– A need to urinate more often when the baby drops down
into a lower position in the pelvis
– Yellow, watery fluid leaking from her nipples, known as
colustrum
– Her navel sticking out
Third Trimester:
For the Mom
 During the third trimester, certain discomforts and mood
changes may occur:
– fatigue or extra energy, or alternate periods of both
– increasingly heavy white vaginal discharge
– more mild lower abdominal pains with uterine tightening and then
relaxing
– more or less of an appetite
– constipation, heartburn, indigestion, gas, and bloating
– headaches, dizziness, or faintness
– more trouble sleeping
– itchy abdomen
– varicose veins
– swelling of the legs, feet, and hands
– increasing clumsiness as shape and balance changes
– anxiety, impatience, and restlessness
– irritability and unusual sensitivity
The Birth Process
 Hormones in mother’s brain signals process
 Contractions begin: strong and regular at 10
minutes apart
– average labor for first births is 8 hours
The Newborn’s First Minutes
 Assessment—Apgar scale
– five factors, 2 points each
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heart rate
breathing
color
muscle tone
reflexes
score of 7 or better: normal
score under 7: needs help breathing
score under 4: needs urgent critical care
Variations
 Parents Reaction
– preparation for birth, physical and emotional
support, position and size of fetus, and
practices of mother’s culture
 Medical Attention
– birth in every developed nation has medical
attention
– 22% of births in U.S. are cesarean section
 removal of fetus via incisions in mother’s abdomen and
uterus
– is medical intervention always necessary?
Birth Complications
 Cerebral Palsy
– brain damage causing difficulties in muscle
control, possibly affecting speech or other body
movements
 Anoxia
– lack of oxygen that, if prolonged, can cause brain
damage or death
First Intensive Care . . .
Then Home
 At the Hospital
– many hospitals provide regular massage and
soothing stimulation; ideally, parents share in
caregiving
 At Home
– complications, e.g., minor medical crises
– cognitive difficulties may emerge, but highrisk infants can develop normally
Mothers, Fathers and a
Good Start
 Strong family support
 Fathers play a crucial role
– may help wives abstain from drugs or alcohol
– can reduce maternal stress
 Parental alliance—commitment by both
parents to cooperate in raising child
– helps alleviate postpartum depression
Mothers, Fathers and a
Good Start
 Parent-infant bond—strong, loving connection
that forms as parents hold, examine, and
feed their newborn
– immediate contact not needed for this to
occur