Transcript SR6e Chapter 4

CHAPTER 4
PRENATAL DEVELOPMENT AND BIRTH
Learning Objectives
• How does development unfold during the
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prenatal period from conception until the time
of birth?
What are the developmental milestones of
prenatal development?
Prenatal Development: Conception
• Conception
– The union of the mature ovum and a sperm
– The genetic material of the cells unite to
form a zygote
Prenatal Development: Infertility
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Infertility
– After a year of trying to get pregnant,
conception does not occur
– Assisted reproduction technologies (ARTs) are
used to increase fertility
• Artificial insemination
– Sperm injected into a woman’s uterus
• In vitro fertilization (IVF)
– Eggs and sperm combined and then
placed in a woman’s uterus
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Stages of Prenatal Development: Germinal
Period
Lasts approximately 2 weeks
Zygote divides through mitosis and forms a
blastocyst that implants into the blood vessels of the
uterine wall
– Only about half of fertilized ova implant
successfully
– Between 15-20% of recognized pregnancies
terminate in miscarriage
– As many as 50% of unrecognized pregnancies are
estimated to terminate with miscarriage, probably
due to genetic defects
Stages of Prenatal Development: Embryonic
Period
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From the 3rd week to the 8th week after conception
Organogenesis
– Formation of every major organ
• Brain and spinal cord, heart, facial features,
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limbs
Layers of the blastocyst differentiate
Sexual differentiation
Stages of Prenatal Development: Embryonic
Period
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Differentiation of the blastocyst during the embryonic
period
– Outer layer becomes the amnion and chorion
• Amnion - membrane that fills with fluid that
cushions and protects the embryo
• Chorion – membrane that surrounds the amnion
and eventually becomes the lining of the placenta
• Placenta – tissue connected to the embryo by the
umbilical cord
– Placenta and umbilical cord – embryo receives
oxygen and nutrients and eliminates carbon
dioxide and metabolic wastes into the mother’s
bloodstream
Stages of Prenatal Development: Embryonic
Period
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Differentiation of the blastocyst during the embryonic
period
– Cells in interior of blastocyst become the
ectoderm, mesoderm, and endoderm
• Ectoderm – evolves into the central nervous
sytem
• Mesoderm – evolves into muscle tissue,
cartilage, bone, heart, arteries, kidneys, gonads
• Endoderm – gastrointestinal tract, lungs,
bladder
Stages of Prenatal Development: Embryonic
Period
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Neural tube defects during the embryonic period
– In approximately 1 of 1,000 pregnancies, the neural
tube fails to close completely
• Spina bifida – part of the spinal cord not fully
encased in the protective covering of the spinal
cord
• Anencephaly – the top of the neural tube does not
close, and the main portion of the brain above the
brain stem does not develop
– Neural tube defects occur 25-29 days after conception
– More common when the mother is deficient in folic acid
Stages of Prenatal Development: Embryonic
Period
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Sexual differentiation during the embryonic period
– Undifferentiated tissue becomes ovaries or testes
• In a genetic male, a gene on the Y chromosome
directs construction of testes
– Embryonic testes secrete testosterone that
stimulates development of the male internal
reproductive system and a hormone that inhibits
the development of a female internal
reproductive system
• In a genetic female, ovaries form
– In the absence of hormones, the embryo
develops the internal reproductive system of a
female
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Stages of Prenatal Development: Fetal
Period
Lasts from the 9th week of pregnancy until birth
Cells proliferate, migrate, and differentiate
– Differentiation of cells occurs according to where cells
migrate
Organ systems continue to grow and begin to function
Sex organs appear during 3rd month of pregnancy
Age of viability reached at about 23 weeks
– When survival is possible if the brain and respiratory
system are sufficiently developed
Weight gain
Organized and adaptive behaviors develop
– Patterns of heart rate, activity level
Learning Objectives
• How and when do various teratogens affect
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the developing fetus?
How can you summarize the effects of
teratogens during the prenatal period?
How do maternal age, emotional state, and
nutrition affect prenatal and neonatal
development?
What about the father’s state - can this
influence development?
Prenatal Environment
• Reciprocal influences
– Transactions between the developing
organism and its physical and social
environments
• Events of the prenatal period have
lifelong effects on physical health and
mental development
– Transactions between the organism and its
environment begin at conception
Caption: The critical periods of prenatal
development
Teratogens
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Any disease, drug, or environmental agent that can
harm a developing organism
Generalizations about the effects of teratogens
– Critical period – effects are worst during the critical
period when an organ system grows most rapidly
– Dosage and duration – the greater the level of
exposure and the longer the exposure, the more
likely is serious damage
– Genetic makeup – susceptibility to harm
influenced by the organism’s and its mother’s
genetic makeup
– Environment – effects depend upon the quality of
both the prenatal and the postnatal environments
Continued on next page.
Caption: Characteristic features of a child with
fetal alcohol syndrome (FAS)
Illustrations of the Principles of Teratology Drugs
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Thalidomide – critical periods for different
deformities
– Missing or deformed limbs; deformed eyes,
ears, nose, heart; missing ears
Tobacco – smoking restricts blood flow to the
fetus and reduces levels of growth factors,
oxygen, and nutrients that reach the fetus
– Associated with higher rates of miscarriage;
slower prenatal growth; increased risk for
prematurity, low birth weight, cleft lips and
palate; increased risk of SIDS
Illustrations of the Principles of Teratology –
Drugs
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Alcohol
– Readily crosses the placenta to affect fetal
development by disrupting the normal process
of neuronal migration
• Fetal alcohol syndrome (FAS) – most
severe
– FAS children have a smaller head and
distinctive facial abnormalities; FAS
children are smaller and lag in physical
growth compared to age-mates
– Central nervous system damage
Illustrations of the Principles of TeratologyAlcohol
• Some children experience milder alcoholrelated effects as a result of prenatal
exposure to alcohol
– Fetal alcohol effects or alcohol-related
neurodevelopmental disorder
• Not all features of FAS but have
physical, behavioral, or cognitive
problems, or a combination of problems
Illustrations of the Principles of TeratologyAlcohol
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The effects of alcohol
– Women who consumer larger quantities are at
greater risk for children with alcohol-related
complications
– Binge-drinking has more negative effects than
consuming the same number of drinks across
multiple occasions
– The effects of alcohol depend upon which systems
are developing at the time of exposure
• 1st trimester – facial abnormalities
• 2nd and 3rd trimesters – growth and brain
development are stunted
Illustrations of the Principles of TeratologyAlcohol
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The effects of alcohol
– Depend upon the woman’s physiology – how
efficiently she metabolizes alcohol and how much
is transmitted to the fetus
– Depend upon co-occurrence of other factors, such
as use of cigarettes and other drugs, adequacy of
prenatal care
– Depend upon the embryo’s genetic makeup and
physical condition and associated ability to resist
and recover from damage
– May depend upon direct and indirect paternal
factors, such as his genetic makeup or quality of
parenting
Illustrations of the Principles of TeratologyDrugs
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Cocaine can cause spontaneous abortion,
premature detachment of the placenta, or fetal
stroke
Cocaine contributes to fetal malnourishment,
retarded growth, and low birth weight
A small proportion of cocaine-exposed infants
experience withdrawal-like symptoms at birth
Cocaine-exposed infants show deficits on
measures of information processing and sensory
motor skills during their first year
Most problems caused by prenatal cocaine
exposure do not persist into childhood
Continued on next page.
Illustrations of the Principles of Teratogens Diseases
• Rubella (German measles) – associated with
blindness, deafness, heart defects, and
mental retardation in exposed infants
– Most dangerous during the 1st trimester
– Damage to the central nervous system,
eyes, and heart is most likely during the
first 8 weeks of pregnancy
– Deafness is likely if the woman contracts
rubella in weeks 6 to 13 of the pregnancy
Illustrations of the Principles of Teratogens Diseases
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Diabetes
– Gestational diabetes arises during the pregnancy
and results from elevated blood glucose levels
• Increased risk of prematurity, stillbirth or
miscarriage, immature lung development, and
large fetal size
Syphilis – sexually transmitted infection
– Can cause stillbirth or miscarriage
– Exposed infants may have blindness, deafness,
heart problems, or brain damage
– Most damaging in the middle and later stages of
pregnancy
Illustrations of the Principles of Teratogens Diseases
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Acquired immunodeficiency syndrome (AIDS) is
caused by the human immunodeficiency virus
(HIV). HIV can be transmitted
– Prenatally, if the virus passes through the
placenta
– Perinatally, by exposure to blood during birth
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– Postnatally, by breast-feeding
If HIV-infected pregnant women are not treated,
approximately 15-35% of infants will be infected
Illustrations of the Principles of Teratogens –
Environmental Hazards
• Radiation
– Doses of radiation used in x-rays and
cancer treatments are capable of causing
mutations, spontaneous abortions, and
birth defects
• Pollutants
– Adverse effects are associated with
prenatal exposure to air pollution, cigarette
smoke, lead, and/or mercury
The Mother’s State – Age
• Very young mothers have higher-than-normal
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rates of birth complications, premature
delivery, and/or stillbirth
• Inadequate prenatal care, alcohol use
Older women are more likely to experience
trouble getting pregnant and have an
increased risk of having miscarriage, stillbirth,
or low-birth-weight infants
– Greater chance of multiple pregnancy,
which has increased risk of fetal mortality
The Mother’s State – Race/Ethnicity
• Non-Hispanic black women have fetal
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mortality rates that are more than twice the
rates experienced by other women
Non-Hispanic black mothers are more
susceptible to premature labor
Reasons for disparity are not completely
understood, but include poorer preconception
health of the mother and less prenatal care
The Mother’s State – Emotional Condition
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If prolonged and severe emotional stress and
anxiety are experienced during pregnancy,
consequences may include
– Faster and more irregular fetal heart rate,
stunted prenatal growth, premature birth, birth
complications
Infants whose mothers were highly stressed
during pregnancy
– Tend to be smaller, more active, more irritable,
more prone to crying, and may experience
delays in cognitive development
– Also associated with increased risk of
developing schizophrenia
The Mother’s State – Nutritional Condition
• Doctors now recommend a well-balanced diet
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with about 300 additional calories per day,
with total weight gain of 25-35 pounds for
normal-weight women
Depending upon when it occurs, malnutrition
can result in stillbirths, neural tube defects,
stunted growth, and cognitive deficits in
infancy and childhood
Folate-enriched cereal products are
associated with a decrease in the incidence
of neural tube defects
Prenatal vitamins are recommended
The Father’s State
• Father’s age
– Children born to teenage fathers have
increased risk of birth complications
– Children born to older fathers have
elevated risk of congenital heart defects,
neural tube defects, and kidney problems
– Likelihood of Down syndrome is greater
when both father and mother are older
– Advanced paternal age (50 and older) is a
risk factor for schizophrenia
Caption: The three stages
of labor: Stage 1: (a)
contractions of the
uterus cause dilation
and effacement of the
cervix. (b) transition is
reached when the
frequency and strength
of the contractions are
at their peak and the
cervix opens
completely. Stage 2: (
c) the mother pushes
with each contraction,
forcing the baby down
the birth canal, and the
head appears. (d) Near
the end of Stage 2, the
shoulders emerge and
are followed quickly by
the rest of the baby’s
body. Stage 3: (e) with
a few final pushes, the
placenta is delivered.
The Father’s State
• Research limited except for genetic
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contribution
Father’s age can also be influential
– Over 35: increased number miscarriages,
heart defects, Down syndrome
– Over 50: higher risk for schizophrenia
Exposure to environmental toxins
– Radiation, anesthetic gases, pesticides
– Damage to genetic material in sperm
Learning Objectives
• What is the typical perinatal environment
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like?
What hazards can occur during the birth
process?
What is the birth experience like from the
mother’s and father’s perspectives, and from
different cultural perspectives?
The Perinatal Environment
• Modern-day birthing practices
– Medical setting and use of technology in
homelike setting
– Parents want greater flexibility and control,
especially control over who will assist with
the delivery
– Presence of supportive people in the
delivery room
The Perinatal Environment - Childbirth
• Childbirth is a three-stage process
– First stage begins with regular uterine
contractions and ends when the cervix is
fully dilated (10 centimeters)
– Second stage is delivery, which begins as
the fetus’s head moves through the cervix
into the vagina and ends when the baby
emerges
– Third stage is delivery of the placenta
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The Perinatal Environment:
Possible Hazards
Anoxia – shortage of oxygen
– Anoxia is dangerous because brain cells
die if they are starved of oxygen for more
than a few minutes
– Severe anoxia can cause poor reflexes,
seizures, heart rate irregularities, breathing
difficulties, memory impairment, increased
risk of learning or intellectual disabilities or
speech difficulties, or cerebral palsy
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The Perinatal Environment:
Complicated Delivery
If assistance with delivery is necessary,
forceps or vacuum extraction (suction) may
be used
Cesarean section is an alternative to normal
vaginal delivery
– Used when the baby is too large or the
mother is too small, the fetus is out of
position, when the placenta prematurely
separates from the uterus, or fetal
monitoring reveals that a birth complication
is likely
The Perinatal Environment:
Complicated Delivery - Cesarean
• In 2007, 32% of U.S. births were Cesarean
• Many Cesareans may be unnecessary
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– Reduced liability and more revenue for the
obstetrician
– Choose a second Cesarean rather than
attempting vaginal birth
– Preference for scheduled birth
For optimal outcome for infants, elective Csections should be performed at 39-40 weeks
The Perinatal Environment:
Complicated Delivery - Medications
• Laboring women may be given
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– Analgesics and anesthetics to reduce pain
– Sedatives for relaxation
– Stimulants to induce or intensify uterine
contractions
Sedatives can cross the placenta to the
infant, and large doses can make the baby
sluggish, irritable, difficult to feed or cuddle,
and smile infrequently
The Mother’s Experience
• Birth stories are unique
– Most women report pain and anxiety, and
77% felt the experience was positive
• Factors that influence the mother’s birth
experience
– Psychological factors such as her attitude
and knowledge, sense of control, and
social support
The Mother’s Experience
• The experience of childbearing is influenced
by its cultural context
– The desirability of having children
– Practices and beliefs about pregnancy and
delivery
• In highly industrialized Western
societies, childbirth is medicalized
The Mother’s Experience
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Baby blues – 60% of new mothers report a
relatively mild, quickly resolved state
– Tearful, moody, irritable, anxious, depressed
Postpartum depression – 1 in 10 new mothers
experience a longer-lasting clinical depression
– Most affected women have histories of
depression
– Additional life stresses and lack of social
support increase the risk
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The Mother’s Experience – Postpartum
Depression
Research suggests that maternal postpartum
depression may affect children’s development
– Less secure attachment
– Violent behavior
– Predisposition to later depression
• Results from maternal behavior that is
unresponsive, possibly hostile, toward the
baby; tired, distracted, not fully engaged with
the infant
Sibling Adjustment
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“Transition to siblinghood”
– Quality of the microsystem
• Example: strong father-child relationship
– Exosystem factors
• Example: parents with strong support less
stressed or tired
– The child’s age, gender, and personality affect
how the child responds to and adjusts to a new
sibling
• Children under age 2 do not show the same
disruption of mother-child attachment that often
occurs when older children acquire a new
sibling
The Father’s Experience
• Fathers experience both positive and
negative emotions
– May experience couvade
• Physiological symptoms associated with
pregnancy
– Possibly experience symptoms of
postpartum depression
– Typically experience postpartum decline in
marital satisfaction
The Father’s Experience
• Accepted, expected in delivery rooms
• Attend prenatal classes with wife
• Experience described as a significant event
• Anxiety, stress common during delivery
• Relief, pride, joy when baby is born
• Sometimes depression following birth
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– Fathers also need support
Disappointed if sex does not resume soon
Learning Objectives
• What are the advantages of breast-feeding?
• Are there disadvantages of breast-feeding?
• How can at-risk newborns be identified?
• What treatments are available to optimize
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development of at-risk babies?
To what extent are the effects of the prenatal
and perinatal environments long lasting?
What factors influence whether effects are
lasting?
The Neonatal Environment
• Ideas about parenting and infant care are
culturally constructed
• Brazelton Neonatal Behavioral Assessment
– Newborn assessment technique that
assesses infant reflexes and infant
responses
– Used to teach parents to understand and
appreciate their infants
The Neonatal Environment
• Breast or bottle?
– All major health organizations advocate for
exclusive breast-feeding for the first 6
months of life
– Health benefits include fewer ear infections
and respiratory tract problems, stronger
lung function, and positive effects on
immune system functioning and weight
gain
The Neonatal Environment
• Identifying at-risk newborns
– Newborns are routinely screened with the
Apgar test, which is a quick assessment of
• Heart rate
• Respiration
• Color
• Muscle tone
• Reflexes
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The Neonatal Environment:
Identifying At-Risk Newborns
Low-birth-weight infants may be born
prematurely or to term but “small for gestational
age”
Prematurity is the leading cause of infant
mortality
Low-birth-weight (LBW) infants are born weighing
less than 2,500 grams or 5.5 pounds
Extremely LBW infants are born weighing less
than 1,000 grams or 2 pounds, 3 ounces
Micropreemie infants are born weighing less than
800 grams or 1.75 pounds
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The Neonatal Environment:
Identifying At-Risk Newborns
Low birth weight is associated with
– Low socioeconomic status
– Ethnicity: African-American mothers are
twice as likely to experience premature
delivery and LBW
– Smoking
– Stress
– Multiple births
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The Neonatal Environment:
Identifying At-Risk Newborns
LBW and extremely LBW children at risk for
– Neuro-behavioral problems, including
blindness, deafness, cerebral palsy, poor
academic achievement, and autism
– Respiratory problems as a consequence of
insufficient surfactant
• Substance that prevents air sacs of the
lungs from sticking together
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The Neonatal Environment:
Identifying At-Risk Newborns
Interventions for LBW infants include surfactant
therapy, breast-feeding, kangaroo care (skin-toskin contact), and massage therapy
Long-term outcomes for LBW infants depend
upon
– Their biological condition, specifically their
health and neurological condition
– The quality of their postnatal environment
• Early intervention programs help parents
learn to provide a growth-enhancing home
environment
Risk and Resilience
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Some infants who are exposed to and affected
by risks recover from their deficiencies
The results of Werner’s 40-year-long Kauai
longitudinal study revealed that
– The effects of prenatal and perinatal
complications decrease over time
– The outcomes of early risk depend on the
quality of the postnatal environment
The study also revealed protective factors
– Personal resources
– Supportive postnatal environment