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Chapter 4
PRENATAL DEVELOPMENT AND BIRTH
FROM CONCEPTION TO BIRTH
• Phases of Prenatal Development
– Period of the zygote: conception through
implantation
– Period of the embryo: 3rd-8th week, organ
formation, heart beat
– Period of the fetus: 9th week-birth
THE PERIOD OF THE ZYGOTE
• Blastocyst: 60-80 cells
– Embryo – inner layer of blastocyst
– Protective/nourishing tissues – outer layer
• Implantation:
– 7-10 days after conception
– Tapping mother’s blood supply through
uterine wall
– Only 25% successfully implant
•
Figure 4.1 The Period of the Zygote
PERIOD OF THE ZYGOTE
• Blastocyst: Support Structures
– Amnion: watertight sac with amniotic fluid
• Cushioning against blows
• Temperature regulation
• Weightless environment for movement
– Yolk sac: early blood cell production
– Chorion: becomes lining of placenta
– Allantois: forms umbilical cord
•
Figure 4.2 The embryo and its prenatal environment.
PERIOD OF THE ZYGOTE
• Purpose of the Placenta
– Semipermeable
• Allowing nutrients and gasses to pass
through
• Blood cells are too large
– Site of all metabolic transactions sustaining
the embryo
THE PERIOD OF THE EMBRYO
• Ectoderm (outer layer)
– Nervous system
– Skin
– Hair
• Mesoderm (middle layer)
– Muscles
– Bones
– Circulatory system
THE PERIOD OF THE EMBRYO
• Endoderm (inner layer)
– Digestive system
– Lungs
– Urinary tract
– Vital organs (pancreas, liver, etc.)
THE PERIOD OF THE EMBRYO
• Developmental Milestones
– 3rd week – neural tube
– 4th week – heart beat
– 7th week – a rudimentary skeleton
– 7th-8th weeks – sexual development
• If male, the Y chromosome triggers a
reaction to produce testes, otherwise
ovaries result
•
Figure 4.3 A human embryo at 40 days.
THE PERIOD OF THE FETUS
• Third Month
– Movement – cannot yet be felt by mother
– Digestive system and excretory systems
functioning
– Reproductive system contains immature
ova or sperm cells
•
Figure 4.4 Rate of body growth during the fetal period. Increase in size is especially dramatic from
the ninth to the twentieth week. ADAPTED FROM MOORE & PERSAUD, 1993.
THE PERIOD OF THE FETUS
• Fourth-Sixth Months
– Sucking, swallowing, breathing
– Movements – felt by mother
– Heart beat can be heard with stethoscope
– Sweat glands functioning
– Vernix – protects skin from chapping
– Lanugo – fine hair helps vernix stick to skin
– Visual and auditory senses are functional
THE PERIOD OF THE FETUS
• Seventh – Ninth Months
– Age of viability - 22-28 weeks – survival
outside the womb is possible
– Weight is 4 pounds (at end of 7th month)
– 9th month – activity slows, sleep increases
– Birth occurs
•
Table 4.1 Brief Overview of Prenatal Development
•
Table 4.1 Brief Overview of Prenatal Development (continued)
POTENTIAL PROBLEMS IN PRENATAL
DEVELOPMENT
• Teratogen – any agent that can harm an
embryo or fetus
• Effects of teratogens
– Most serious when structure is forming
– Susceptibility to harm is influenced by
genetic makeup of mother and embryo
– Same defect can be caused by different
teratogens
POTENTIAL PROBLEMS IN PRENATAL
DEVELOPMENT
• Effects of teratogens, continued
– One teratogen can cause different defects
– Longer exposure/higher dose, more harm
– Father’s exposure may affect embryo
– Long-term effects depend on postnatal
environment
– Some effects not apparent until later in life
•
Figure 4.5 The critical periods of prenatal development. Each organ or structure has a critical
period when it is most sensitive to damage from teratogens. Dark band indicates the most
sensitive periods. Light band indicates the time that each organ or structure is somewhat less
sensitive to teratogens, although damage may still occur. ADAPTED FROM MOORE & PERSAUD,
1993.
TERATOGENS
• Diseases of the pregnant woman
– Rubella (German measles)
• Blindness, deafness, cardiac
abnormalities, mental retardation
• Most dangerous during 1st trimester
• No woman should try to conceive unless
they have had rubella or been
immunized
TERATOGENS
• Toxoplasmosis –
– Caused by eating undercooked meat,
handling cat feces
– Causes eye and brain damage during first
trimester
– Induces miscarriage later in pregnancy
•
Table 4.2 Common Diseases That May Affect an Embryo, Fetus, or Newborn
TERATOGENS
• Sexually Transmitted Diseases
– Syphilis
• Cannot be transmitted to fetus until 18th
week
• Early treatment prevents harm
• Damages eyes, ears, bone, heart, brain
• Can result in miscarriage
TERATOGENS
• Sexually Transmitted Diseases
– Genital Herpes
• Can cross placenta
• Most infections occur during birth
• Kills 33% of infected newborns
• Causes blindness, brain damage and
other neurological problems in 25-30%
• Cesarean delivery prevents infecting
newborn
TERATOGENS
• Sexually Transmitted Diseases
– Acquired Immunodeficiency Syndrome
(AIDS)
• Caused by HIV
• Passed through placenta, while giving
birth, or while breast-feeding
• Only 25% of those at risk are infected
• ZDV reduces transmission by 70%
• 50% of HIV infected infants live past 6
TERATOGENS
• Drugs
– Thalidomide
• Used to prevent nausea and vomiting
• Tested on animals and was “safe”
• Caused birth defects (for some) if taken
during first 2 months of pregnancy
–Eyes, ears, noses, hearts
–Phocomelia – parts of limbs missing,
feet or hands connected to torso
TERATOGENS
• Drugs
– Aspirin – growth retardation, infant death
– Ibuprofen – 3rd trimester – pulmonary
hypertension, prolonged delivery
– Caffeine – miscarriage, low birth weight
– Lithium – 1st trimester – heart defects
– Oral contraceptives – heart defects
– Diethylstilbestrol (DES) – delayed effects in
reproductive system, primarily female
TERATOGENS
• Drugs
– Alcohol – compromises functioning of the
placenta
• Fetal alcohol syndrome (FAS)
–Microcephaly
–Malformation of heart, limbs, joints
and face
–Hyperactivity, seizures, tremor
–Lower IQ, major adjustment problems
TERATOGENS
• Alcohol
– Fetal Alcohol Effects (FAE)
• Social drinking (1-3 per day)
• Greatest risk – binge drinking (5+)
• Slow physical growth, poor motor skills,
attention difficulties, verbal learning
difficulties
• Subnormal intellectual performance
• Father’s drinking may also be harmful
TERATOGENS
• Cigarette Smoking
– Cleft lip
– Abnormal lung functioning
– Miscarriage
– Low-birth-weight
– Ectopic pregnancy – implantation in
fallopian tube
– Sudden Infant Death Syndrome
– Higher concentration of nicotine in fetus
TERATOGENS
• Marijuana
– Emotional regulation in males
– Poorer reading/spelling at 10 years old
– More depression/anxiety
• Narcotics (heroin, methadone)
– 60-80% born addicted
– Breathing/swallowing coordination
– Normal developmental progress by age 2,
although boys remain vulnerable
TERATOGENS
• Cocaine
– Miscarriage, premature birth
– Sleep disturbances, very irritable
– Lower IQ
– Poor language development skills
– Negative effects also due to
• Maternal vocabulary
• Home environment
• Exposure to additional teratogens
•
Table 4.3 Partial List of Drugs and Treatments Used by the Mother That Affect (or Are Thought to
Affect) the Fetus or the Newborn
TERATOGENS
• Environmental Hazards
– Radiation – death, mental retardation
– Chemicals/pollutants
• Lead/mercury – deformities, mental
retardation
• PCB’s – less neurologically mature
–Prenatal and postnatal effects
• Father’s exposure also harmful
•
Figure 4.6 Average cognitive test performance at age nine, based on child’s level of exposure to
PCB prenatally and through breast feeding. Light bars indicate children who were exposed to low
levels of PCB, dark bars are children who were exposed to high levels of PCB.
MATERNAL CHARACTERISTICS
• Pregnant Woman’s Diet
– Total weight gain 25-35 pounds
• 1st trimester malnutrition – miscarriage,
spinal cord malformation
• 3rd trimester malnutrition – low-birthweight, small heads
– Dietary supplements and stimulation can
reduce effects of prenatal malnutrition
•
Figure 4.7 Incidence of infant mortality in the first 12 months for babies born to Dutch
mothers who had experienced famine during World War II. ADAPTED FROM STEIN
& SUSSER, 1976.
MATERNAL CHARACTERISTICS
• Pregnant Women’s Diet
– Magnesium & Zinc – reduce complications
– Folic acid – reduces Down Syndrome,
spina bifida, anencephaly
– Medical supervision is necessary, as
excessive vitamin/mineral supplements
can be harmful
MATERNAL CHARACTERISTICS
• Pregnant Woman’s Emotional Well-Being
– Prolonged and severe emotional stress
• Stunted prenatal growth
• Premature delivery
• Irritable
• Irregular feeding, sleeping
• Causal relationship in animals
•
Figure 4.8 Percent of bath time infants spent fussing and crying. The figure compares infants
whose mothers experienced high levels of cortisol (a hormone related to stress) to infants whose
mothers experienced low levels of cortisol during pregnancy.
•
Figure 4.8 Percent of bath time infants spent fussing and crying. The figure compares infants
whose mothers experienced high levels of cortisol (a hormone related to stress) to infants whose
mothers experienced low levels of cortisol during pregnancy. (continued)
MATERNAL CHARACTERISTICS
• Pregnant Women’s Emotional Well Being
– Prolonged stress
• Stress hormones – impede oxygen and
nutrients to fetus
• Weaken immune system
• Linked to poor eating, smoking, drug
and alcohol use – all harm fetus
• Counseling to manage/reduce stress
• Moderate levels may aid development
MATERNAL CHARACTERISTICS
• Pregnant Woman’s Age – 16-35 is optimal
– 15 years old and younger
• Impoverished backgrounds
–Poor nutrition, high stress, little
prenatal care
• Little risk if good prenatal care is present
– Older than 35
• Increased risk of miscarriage
• Risks not reduced by prenatal care
BOX 4.1 - FOCUS ON RESEARCH: FETAL
PROGRAMMING
• Fetal Programming Theory – brain and other
systems are programmed in a manner that is
adaptive for the uterine environment
– Persists at birth, but what’s adaptive in the
uterus may not be after birth
– Focus is on subtle changes in metabolism,
endocrine and autonomic functions
– Result may be increased susceptibility to
diseases in adulthood, like diabetes
PREVENTION OF BIRTH DEFECTS
• 95% of newborns are normal
• Many of remaining 5% have minor congenital
problems that are temporary or correctable
• Each pregnancy is different
– Genetic makeup
– Prenatal environment
•
Table 4.4 Reducing Likelihood of Congenital Disorders.
BIRTH AND THE PERINATAL ENVIRONMENT
• Perinatal environment – environment
surrounding birth
– Medications
– Delivery practices
– Social environment
THE BIRTH PROCESS
• First stage of labor
– Contractions 10-15 minutes apart
– Cervix fully dilates
• Second stage of labor – delivery
– Head passes through cervix
– Baby emerges from body
• Third stage of labor – afterbirth
– Placenta expelled from body
•
Figure 4.9 The three stages of childbirth.
THE BABY’S EXPERIENCE
• Stressful, but assists with breathing
• Baby’s Appearance - 20 inches long, 7-7.5
pounds, bluish, a bit misshapen
• Assessing the Baby’s Condition
– Apgar test
• Heart rate, respiratory effort, muscle
tone, color, reflex irritability
• Scored 0-10 (0-2 each)
• 7+ good, 4 and lower needs attention
•
Table 4.5 The Apgar Test
THE BABY’S EXPERIENCE
• Assessing the Baby’s Condition
– Neonatal Behavioral Assessment Scale
• Several days after birth
• 20 inborn reflexes
• Reactions to comforting and social
stimuli
• Unresponsiveness may indicate
neurological problems
• Can be a parent teaching tool
LABOR AND DELIVERY MEDICATION
• Some medication used by 95% of mothers
– Reduce pain, induce contractions, relax the
mother
– Can reduce the ability to push effectively
– Can make babies lethargic and inattentive
– Drugs in appropriate doses can increase
comfort without disrupting delivery
BOX 4.2 – APPLYING RESEARCH TO YOUR
LIFE: VARIATIONS IN BIRTHING PRACTICES
• Pokot of Kenya – community celebration
• Uttar Predesh in India – shameful, disgusting
• U.S. typically a hospital procedure
– Natural / prepared childbirth: focus is on
support, relaxation – reduces medication
– Home births – shorter labors, less meds,
safe if smooth pregnancy, trained midwife
– Alternative birthing centers – homelike
setting in hospital
THE SOCIAL ENVIRONMENT
SURROUNDING BIRTH
• Mother’s experience
– First 6-12 hours – sensitive period for
emotional bonding (not essential)
– Maternity blues – 40-60% of mothers
– Postpartum depression – 10% of mothers
• Should seek professional help
• Depression affects outcomes of both
mother and infant
THE SOCIAL ENVIRONMENT
SURROUNDING BIRTH
• The Father’s experience
– Engrossment – intense fascination, desire
to touch, hold and caress
– Early contact with newborn can make
father feel closer to partner, positive
support for mother
POTENTIAL PROBLEMS AT BIRTH
• Anoxia – oxygen deprivation
– Umbilical cord becomes tangled
– Breech position
– Placenta separation
– RH factor incompatibility – now
preventable
– Can cause neurological damage,
permanent disabilities
– Increased risk of adult heart disease
POTENTIAL PROBLEMS AT BIRTH
• Complications of Low Birth Weight
– Preterm – born more than 3 weeks early,
but appropriate weight for time in womb
– Small for date – underweight due to slow
fetal growth – greater risk than preterm
• Causes include smoking, drug use,
stress, lack of prenatal care, multiple
births, social support
• [
•
Figure 4.10. Gestational age at birth for singletons, twins, and triplets.
POTENTIAL PROBLEMS AT BIRTH
• Short-term Consequences of Low Birth
Weight
– 40-50% weighing less than 2.2 pounds die
– Brain development and neural pattern
formation in preterm infants differs
– Breathing difficulty due to lack of surfactin,
or respiratory distress syndrome
– Spend time in isolettes
– Can be frustrating to care for
POTENTIAL PROBLEMS AT BIRTH
• Interventions for Preterm Infants
– Early acquaintance programs – touching,
rocking, talking, are developmentally
beneficial
– Parents can be taught how to be sensitive
and responsive to preterm infants
– Combined with stimulating day care
programs help, improves cognitive growth
and reduces behavioral disturbances
POTENTIAL PROBLEMS AT BIRTH
• Long-term Consequences of Low Birth
Weight
– Depends on postnatal environment
• Stimulating home, very good
• Less stable home or being economically
disadvantaged
–Smaller, emotional problems
–Deficits in intellectual/academic
performance
•
Figure 4.11. Age trends in intellectual development for low-birth-weight twins from middle-class
(high SES) and lower socioeconomic (low SES) backgrounds. ADAPTED FROM WILSON, 1985.
REPRODUCTIVE RISK AND CAPACITY FOR
RECOVERY
• Werner & Smith – Kauai Longitudinal Study
– At birth,
• 16% severe complications, 31% mild
– Age 2 – severity predicted developmental
progress, but emotional support and
educational stimulation improved outcomes
– Age 10 – severity not very predictive, home
environment now predictive
APPLYING DEVELOPMENTAL THEMES TO
PRENATAL DEVELOPMENT AND BIRTH
• Active child – moves, practices in womb
• Nature/nurture interaction – effects of
teratogens
• Qualitative changes – stages of birth
• Quantitative changes – fetal development
• Holistic nature of development – prenatal
development affects all future development;
social support during birth has consequences
for future development