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PRENATAL DEVELOPMENT AND BIRTH
FROM CONCEPTION TO BIRTH
• Phases of Prenatal Development
– Period of the zygote: conception through
implantation (10–14 days)
– 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 3.1 The Period of the Zygote
THE 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 3.2 The embryo and its prenatal environment.
THE PERIOD OF THE ZYGOTE
• 3rd – 8th weeks of development
• 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 3.3 A human embryo at 40 days.
THE PERIOD OF THE FETUS
• Last 7 months of pregnancy
• Third Month
– Movement – cannot yet be felt by mother
– Digestive system and excretory systems
functioning
– Reproductive system contains immature ova or
sperm cells
•
Figure 3.4 Rate of body growth during the fetal period. Increase in size is especially dramatic from the 9th
to the 20th week. Adapted from Before We Are Born, 4th ed., by K. L. Moore & T. V. N. Persaud, 1993, p. 89.
Philadelphia: Saunders. Adapted with permission of the author and publisher.
THE PERIOD OF THE FETUS
• The 4th through 6th 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
• The 7th through 9th Months
– Age of viability - 22–28 weeks – survival
outside the womb is possible
– Weight is four pounds (at end of 7th month)
– 9th month – activity slows, sleep increases
– Birth occurs
•
Table 3.1 A Brief Overview of Prenatal Development
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 3.5 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
Before We Are Born, 4th ed., by K. L. Moore & T. V. N. Persaud, 1993, p. 89. Philadelphia: Saunders. Adapted with
permission of the author and publisher.
TERATOGENS
• Diseases of the pregnant woman
– Rubella (German measles)
• Blindness, deafness, cardiac abnormalities, mental
retardation
• Most dangerous during first trimester
• No woman should try to conceive unless they have
had rubella or been immunized
•
Table 3.2 Common Diseases That May Affect an Embryo, Fetus, or Newborn.
TERATOGENS
• Toxoplasmosis –
– Caused by eating undercooked meat, handling
cat feces
– Causes eye and brain damage during first
trimester
– Induces miscarriage later in pregnancy
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
two 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
– 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 3.3 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
MATERNAL CHARACTERISTICS
• Pregnant Woman’s Diet
– Total weight gain 25–35 pounds
• 1st trimester malnutrition – miscarriage, spinal cord
malformation
• 3rd trimester malnutrition – low-birth-weight, small
heads
– Dietary supplements and stimulation can
reduce effects of prenatal malnutrition
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
•
Figure 3.6 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 Woman’s Emotional Well-Being
– Prolonged and severe emotional stress
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•
•
•
•
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. Reprinted from Early Human Development, 74, Weerth et al., “Prenatal Maternal Cortisol
Levels and Infant Behavior During the First 5 Months,” 151-193, Copyright 2003 with permission from Elsevier.
•
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. Reprinted from Early Human Development, 74, Weerth et al., “Prenatal Maternal Cortisol
Levels and Infant Behavior During the First 5 Months,” 151-193, Copyright 2003 with permission from Elsevier.
MATERNAL CHARACTERISTICS
• Pregnant Women’s Emotional Well-Being
– Prolonged stress
• Associated with sensitive period (12–22 weeks)
– Alter blood flow, 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
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 3.4 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 3.8 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 3.5 The Apgar Test. Note: Letters in Apgar are an acronym for the test’s five criteria: A = Appearance,
P = Pulse, G = Grimace, A = Activity level, R = Respiratory effort.
THE BABY’S EXPERIENCE
• Assessing the Baby’s Condition
– Neonatal Behavioral Assessment Scale
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•
•
•
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
APPLYING RESEARCH: CULTURAL AND HISTORIC
VARIATIONS IN BIRTHING PRACTICES
• Pokot of Kenya – community celebration
• 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
• Siblings’ experiences
– Sibling rivalry
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
• Prematurity and Low Birth Weight
– Preterm – born more than three 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 3.9. Gestational age at birth for singletons, twins, and triplets. Reprinted from Early Human
Development, 78, Amiel-Tison et al., “Fetal Adaptation to Stress: Part 1: Acceleration of Fetal Maturation
and Earlier Birth Triggered by Placental Insufficiency in Humans,” 15-27, Copyright 2004, with permission
from Elsevier.
POTENTIAL PROBLEMS AT BIRTH
• Short-term Consequences of Low Birth
Weight
– 40-50% weighing less than 2.2 pounds die
– Spend time in isolettes
– Slow to initiate social interaction
– Risk of forming less secure emotional
attachments
– More likely to become targets of child abuse
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 in stature, emotional problems
– Deficits in intellectual/academic performance
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 – teratogens
Qualitative changes – stages of birth
Quantitative changes – fetal development
Holistic nature of development – prenatal
development affects future development;
social support during birth has
consequences for future development