Transcript File

General facts about pregnancy
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Pregnancy lasts for 266 days on average.
Doctors count first day last menstrual period (LMP)—
not the day you conceive--as the first day of
pregnancy
According to the medical model, pregnancy lasts 40
weeks; it’s actually 38 weeks from the time of
conception until birth (on average).
Three distinct periods of development
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Period of the zygote (weeks 1-2)-also called the
germinal period
Period of the embryo (weeks 3-8)
Period of the fetus (weeks 9-38)
**These are not the same as first, second, and third
trimester
Period of the zygote (germinal period)
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First two weeks after conception
Period of rapid development
Zygote becomes the blastocyst--hollow inner layer of
cells, which implants into the uterine lining on days 7-9
Trophoblast—outer layer of cells; becomes the
placenta
Differentiation of cells begin
30-50% of conceptions don’t make it through this
period
Placenta is formed at the end of this stage
Life support systems of the embryo
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Amnion—sac filled with clear fluid in which embryo
floats
Placenta—disk-shaped group of tissues that allows
food and oxygen to reach the embryo; carries waste
products away
Umbilical cord—contains two arteries and one vein
that connect the baby to the placenta.
Embryo’s and mom’s blood supplies come in close
contact but never mix directly
Placenta at around 8 weeks
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Placenta at birth
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The placenta is the baby’s life support system
throughout pregnancy.
Developmental trends
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Cephalocaudal—from head to tail; development
occurs head-down
Head region accounts for 50% of total length
during the first month
Proximodistal—development occurs “from the inside
out”—midline outward
Same pattern of development throughout childhood
Period of the embryo
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Dramatic and rapid growth takes place
Groundwork for all body structures and internal
organs is laid
By the end of this period, all of the structures and
internal organs a baby is born with are already
formed
By the end of this period, embryo loses its gills and
tail and looks more human.
Cellular differentiation in the embryo
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Three distinct layers are formed:
 Ectoderm:
outer layer of the embryo—gives rise to the
nervous system, skin, hair, teeth, nails, and teeth
 Mesoderm: middle layer—gives rise to muscles,
skeleton, circulatory, and excretory systems
 Endoderm: inner layer which gives rise to the
respiratory system, liver, and pancrease
Organogenesis during the first four
weeks
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The process of organ formation
3rd week: neural tube forms (becomes spinal cord)
21 days—eyes appear
24 days—heart cells begin to differentiate
4th week—urogenital system is apparent; arm & leg
buds emerge
Primitive mouth, intestinal tract, liver form
Primitive brain forms
Embryo is 1/6 of an inch long
The embryo at 6 weeks
Neural Induction
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The process of beginning the development of the
nervous system at the start of the third week
Starts with a chemical signal from the mesoderm to
the ectoderm, causing a portion of the ectoderm to
become the neural plate
Nervous System Development
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Begins with neural induction of the neural plate
Neural tube then forms; top becomes the brain and
the rest becomes the spinal cord.
Even in the early days of neural tube development,
neurons know to what part of the brain they’ll travel
and what time of nerve cell they’ll become (motor,
vision, hearing, etc.)
Speed of Neural Development
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Cell proliferation: nerve cells begin to form in the
neural tube at a rate of 250,000 per minute for the
entire pregnancy. 30,000 synapses are formed every
second. Baby is born with 100 billion neurons.
Cell migration: begins during 7th week; neurons begin
their destination in the developing brain.
Some neurons travel distances equal to the distance
between Boston and San Francisco!
1000 trillion connections in the brain begin to form,
followed by a pruning process that continues throughout
life.
Embryonic development at 8 weeks
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Embryo is 1 ½ inches long and 1 oz. In weight
Arm and leg differentiate further
Elaborate peripheral nervous system in place
Glandular system operating
Internal sex organs developed (NOTE: Sex is
determined at conception.)
Embryo can move, but movements can’t be felt by
mom yet.
95% of body parts are differentiated (arms, legs,
beating heart, nervous system, etc.) by the 8th week.
8-week-old embryo
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Early Period of the fetus (weeks 9-12)
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Embryo becomes a fetus when bone replaces
cartilage
Facial features become distinct, human-like
Vocal cords, nails, lungs have formed
External genitalia are identifiable
Heartbeat can be heard
Baby can urinate
Baby can smile, frown, suck, and swallow
About 3 inches long; weighs about 1 ounce
Middle months of period of the fetus
(5th-6th month)
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12-15 inches long, 12-32 ounces
Grasping reflex; baby sucks thumb
Lung breathing is possible
Sleep/wake cycles similar to newborn’s
Eyes and ears are sensitive to light and sound; visibility is
obtained.
Very sensitive to touch
All neurons present by 24 weeks’ gestation
Rapid growth during 6th month; slows during 7th month.
Vernix and lanugo
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Appear in 5th-6th month
Vernix—cheeselike covering to protect skin from
chapping
Lanugo—white, downy hair on body to protect skin
from chapping
Fetus with vernix and lanugo
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Vernix and lanugo are often still present at birth,
especially if the baby is preterm.
Age of viability
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This is the age by which the fetus can survive outside
the womb
Usually this is between 22-26 weeks’ gestation
By the 24th week, the fetus has a 50% chance of
survival.
Fetal Development by Month
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3rd month: sex organs appear. Visible by 12 weeks.
4th month: rapid growth; red blood cells develop; active
sucking reflex
5th month: hears sound, sleeps, 10-12 oz. long, 1 pound
6th month: rapid growth, 12-14 inches, 2 pounds
7th month: growth slows; viability attained
8th and 9th month: baby plumps up, senses ready to
function, brain is 25% of adult weight
Last months (7-9) of pregnancy
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Lungs gradually mature
Rapid brain development causes sensory &
behavioral capacities to expand
Antibodies are transferred from mom to baby
Baby becomes better able to regulate temperature
Gains 3.5 pounds in fat
Engagement (baby’s head in birth canal) by 36 weeks
Baby weighs on average 7 ½ pounds at birth
Ethical Issues during Pregnancy
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Embryonic adoption…what to do with frozen embryos
that the biological parents do not want
Stem cell research
Embryonic stem cells are those cells that have been removed
from the inner cell mass of the blastocyst about 4 days after
conception.
 These cells are called pluripotent cells, which are capable
of becoming almost any cell in the human body until they
begin to specialize. If left alone, the pluripotent cells
develop into a viable embryo.
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Sex Differences in Utero
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Males are more physically active—they remain more
active through childhood
Females are more sensitive to external stimulation
Females advance more rapidly in skeletal
development and are 1-2 weeks ahead of males in
bone development at birth. Trait remains through
early adolescence.
More boys are conceived than girls, but the birth rate
is roughly equal (105 males to 100 females)
Mozart effect
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The finding that exposing fetuses and babies to
classical music (specifically Mozart) is associated
with greater math and spatial ability test scores.
The finding has been disputed recently. Seems to
increase math skills in adults for about 30 minutes
after listening to it.
Sounds and tastes infants prefer
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They prefer their mother’s voice over all others
No preference in father’s voice over other men’s
Fetuses develop taste preferences and aversions;
strong tastes such as garlic are present in the amniotic
fluid (also in breast milk)
Fetal tastes may influence later taste preferences.
Habituation
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Getting accustomed to a certain stimulus in the
womb
Fetuses at 26 weeks of age show habituation to
repeated stimuli
Some psychologists think that how quickly a fetus
habituates to a routine stimulus predicts future
intelligence. This is debatable.
Teratogens
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Any environmental agent that can interfere with the
process of normal growth (even vitamins can be
teratogens)
Especially harmful in the embryonic stage because this
is when organs are being formed.
Effects of a teratogenic substance are worse on the
body part or organ systems that are being formed at
the time of exposure
Does a teratogen always cause
damage?
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No—a specific teratogen usually does NOT cause a
specific birth defect.
Three factors influence the effects of a teratogen:
Dose—the greater the dose, the greater the effect.
 Genetic susceptibility—both the mother’s and baby’s
genotypes influence vulnerability.
 Timing—Teratogens do more damage at specific times of
development.
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Times of greatest vulnerability when
exposed to teratogens
Brain: 15 to 25 days after conception
Eyes: 24-40 days after conception
Heart: 20 to 40 days after conception
Legs: 24-37 days
*Each body part has its own critical time of formation.
Only about half of all potential effects of a teratogen
are evident at birth.
Why are teratogens harmful to baby
but not to Mom?
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Mother weighs a lot more
Mother’s organs aren’t developing like the baby’s
are
The placenta and immature fetal liver may be
unable to convert a harmful substance to a harmless
one
STORCH
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Refers to the following infectious diseases that are
teratogens
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Syphilis (50% die; blindness, retardation, deafness)
Toxoplasmosis (protozoan virus transmitted by cats; neurological
problems, preterm delivery, or miscarriage)
Other infections (flu, chicken pox, measles, etc.)
Rubella (German measles; blindness, deafness, retardation,
death)
Cytomegalovirus (CMV..no treatment for this…casus retardation,
blindness, deafness, possibly death)
Herpes (Herpes II is the genital kind; contracted in birth canal;
child develops symptoms in 1st week of life. Affects CNS.)
Examples of teratogens
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Over-the-counter, prescription, and illegal drugs
Caffeine—medical opinions differ as to whether it’s
harmful or not (4 cups or more of coffee a day is
considered harmful)
Tobacco—associated with low birth weight,
miscarriage, SIDS, asthma, and childhood cancer
Alcohol—can result in fetal alcohol syndrome
Maternal malnutrition—smaller brain size
Maternal stress—associated with miscarriage,
preterm labor, low birth weight
Fetal alcohol syndrome
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Involves mental retardation, impaired motor
coordination, poor attention and memory, and
certain physical characteristics.
Heroin
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Well-documented effects: behavioral disturbances in
children of heroin-addicted mothers
Infants have tremors, show irritability, abnormal
crying, sleep disturbances, and impaired motor
control.
These are all symptoms of heroin withdrawal.
Many still have behavioral problems at 1 year old,
and studies show attention deficits later in
development.
Methamphetamine (meth)
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Babies are at significant risk of infant mortality, low
birth weight, and developmental and behavioral
problems.
Respiratory difficulties, neurological problems, poor
cognitive functioning, and abuse and neglect by
parents are common.
Meth use during pregnancy is increasing and is now
considered an even greater problem than cocaine
use.
What about fish?
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Some fish, especially large fish such as tuna, sharks,
swordfish, etc., contain high levels of mercury.
Mercury crosses the placenta easily and leaves the
infant highly sensitive to brain and nervous system
defects.
FDA in 2004 advised women of childbearing age
and young children not to eat shark, swordfish, king
mackerel or tilefish. They can eat up to 12 ounces (2
meals) a week of shrimp, canned light tuna, salmon,
pollock, & catfish.
Maternal Age
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Considered a teratogen
Over age 35, problems increase dramatically (more
trouble getting pregnant, risk of birth defects &
chromosomal problems)
Teenage mothers show the same problems as older
mothers, especially in rates of Down’s syndrome
What about paternal age?
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Older fathers have children who face increased risk
of certain birth defects, including Down syndrome,
dwarfism, Marfan syndrome (involves head & limb
deformities), and perhaps autism.
When both parents are older (mom over 35; dad
over 40), the risk of miscarriage is greater.
Genital herpes
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Newborns contract genital herpes when they pass
through the birth canal of an infected mother.
About 1/3 of the babies die, and another ¼ are
brain damaged if delivered by a mother with active
herpes.
A C-section may be performed if mother has an
active case of herpes near the time of delivery.
AIDS
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Mothers can transmit HIV to their infants in one of 3
ways:
Across the placenta
 During delivery through contact with maternal blood/fluids
 Postpartum through breastfeeding
 Infants can be infected but asymptomatic; they can still
develop symptoms up to 15 months old.
Risk is reduced by giving pregnant HIV-infected moms AZT
during pregnancy and the baby AZT after birth; a
“bloodless” C-section can also help.
An infected mother will pass HIV along 30-50% of the time
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AIDS in babies
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AIDS embryopathy may develop when the virus is
transmitted.
Results in growth retardation, microcephaly, flat nose,
widespread, upward-slanted eyes.
Associated with higher rates of preterm disease, low
birth weight, and miscarriage.
AIDS has slower incubation period in fetuses than adults.
Symptoms often appear as early as 6 months (weight
loss, diarrhea, fever, chronic infections).
Babies rarely survive more than 5-8 months once
symptoms appear.
AIDS embryopathy
The Rh problem
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If a woman has Rh - blood and the father has Rh +, the
fetus may be born with Rh + blood.
Antibodies in the mother may attack the fetus as being
“foreign.”
Can result in miscarriage, stillbirth, anemia, jaundice, heart
defects, brain damage, or death soon after birth.
First Rh-positive baby is usually not affected; subsequent
babies are.
Moms are given a RhoGam vaccine within 3 days of
delivery to prevent antibodies from being produced.
Prematurity
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Babies born 3 weeks or more before the end of
pregnancy OR who weigh less than 5.5 pounds
Birth weight is best predictor of infant survival and
healthy development
Best scenario is to be at least 2 pounds at birth and
32 weeks’ gestation
Preterm babies are more difficult infants than other
babies are and have a greater risk for abuse.
Causes of Prematurity
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Low socioeconomic status: 1 in 4 babies are born in
underdeveloped countries
Infections
Smoking and drinking
Mom’s age (under 17 or over 35)—high correlation
Cervical problems, high blood pressure, unusual
stress, diabetes, heart diseases
Often impossible to determine
Prematurity Stereotyping
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The tendency for people to view premature babies as
weaker, more vulnerable, and less competent than fullterm babies, even after the premature babies have
caught up developmentally with full-term peers
Developmental milestones may, in fact, be reached a
little more slowly in preterm babies.
Experiment showed that people judged a 9-month-old
healthy looking baby as “weaker, less sociable, and less
cognitively competent” if told the baby had been
premature.
Micro-preemie (at the very edge of
viability)
This infant was born at 23 weeks and weighed 1 lb.
2.6 oz.
The same preemie at 4 years
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Although asthmatic and slightly developmentally
delayed, she’s doing great!
How much weight should mother gain
during pregnancy?
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Normal weight woman: 25-35 pounds
Overweight woman: 15-25 pounds
Underweight woman: needs to gain to ideal weight
PLUS 28-40 pounds
Exercise is okay, as long as it’s not too strenuous.
(Mild to moderate only)
No exercises lying on the back after the first
trimester.
Avoid exercise that affects balance.
Common Prenatal Tests
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Amniocentesis: can be done from 15th week of
pregnancy on. Involves taking a fluid sample of the
amniotic fluid.
Alpha-feta Protein Test: (AFP)—this is a protein
produced by baby’s liver; can detect spina bifida
and possibly Downs Syndrome, although there are
many false positives.
Chorionic villi sampling (CVS)—can test genetic
structure as early as 9-10 weeks.
Three stages of birth
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Stage 1: cervix dilates and effaces (thins out)…goes
from totally closed to 10 cm (completely open). Lasts
12-14 hours on avg. in a first birth, 4-6 hours in
subsequent births
Stage 2: the stage where the baby is pushed out.
Lasts around an hour in a 1st birth, 15-20 minutes in
later births.
Stage 3: placenta (“afterbirth”) is delivered. Usually
occurs 5-10 minutes after baby is born; this is usually
not felt by the mother.
C-sections
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C-section rates are currently 20-25% in US; varies by
hospital
Main reason for C-section: having had a prior Csection.
Fetal distress, prematurity, certain maternal illnesses
(such as HIV), birth canal being too narrow, and labor
that doesn’t progress are reasons for C-sections.
Push by some OB/GYNs to give women the right to
elective C-sections.