Transcript Theories of Human Development

Prenatal Development
and Birth
Chapter 4
Periods of Prenatal Development

The Period of
the Zygote
– Zygote 
blastocyst
– Cell
differentiation
– % of
blastocysts
that fail to
implant?
Periods of Prenatal Development

The Period of the Zygote (con’t)
– Outer layer of blastocyst develops into:
 Amnion
 Chorion
 Placenta
 Umbilical cord
**note that these structures actually develop during
the period of the embryo
Periods of Prenatal Development

The Period of the Embryo
– From implantation (week 3) to week 8
– Embryonic disk is already differentiating into:
 Ectoderm (nervous system, skin, hair, sensory
receptors
 Mesoderm (muscles, bones, circulatory system,
reproductive system, excretory system)
 Endoderm (digestive system, lungs, urinary tract,
other internal organs)
Periods of Prenatal Development

The Period of the Embryo (con’t)
– By 4th week, heart has formed and begun to
beat
– Becomes more human in appearance during
2nd month
– Sexual differentiation during 7th – 8th weeks
Periods of Prenatal Development

The Period of the Fetus
– Final 7 months of pregnancy
– Fetus
– Digestive and excretory systems functional
– Sex detected by ultrasound by end of 3rd
month
– Kicks and movements strong enough to be
felt
– Organ systems mature rapidly during final 3
months
Periods of Prenatal Development

The Period of the Fetus (con’t)
– Viable between 22-28 weeks
– Receives antibodies
– Assume upside-down position in final weeks
 Weight of head
 Shape of uterus
Trends in Development

Cephalocaudal Trend

Proximodistal Trend
Teratogens
Root word means “formation of monsters”
 Harm isn’t always simple or
straightforward
 Amount and length of exposure
 Genetic makeup of mother/baby
 Presence of several negative factors

Teratogens
Same defect  different teratogens
 One teratogen  different defects
 Some effects seen later

Teratogens
Age of baby
 Sensitive period

Teratogens

Paternal influences often overlooked
– Direct and indirect effects
– Second hand smoke
– Chemicals
– Cocaine can “hitchhike”
– Smoking, alcohol, drug use  sperm
– Diets low in vitamin C
Other Factors
Exercise
 Nutrition
 Emotional stress
 Rh blood incompatibility
 Maternal/Paternal age

– Older  less fertile, more risk of disorders
– Younger  increased risk of prematurity,
infant death
Other Factors
Infectious Diseases
 Prenatal Care
 Previous births

Perinatal Environment
Environment surrounding birth
 Stages of childbirth

– Contractions
– Delivery
– Afterbirth

Newborn appearance
Perinatal Environment

Assessing the Newborn
– Apgar scale
– 1 minute and 5 minutes after birth
Perinatal Environment

Assessing the Newborn
– Neonatal Behavioral Assessment Scale (NBAS)
 Several days after birth
 20 inborn reflexes
 Reactions to comforting and social stimuli
 Unresponsiveness may indicate neurological
problems
 Can be a parent teaching tool
Perinatal Environment

Complications
– Anoxia
 Severe  cerebral palsy, mental retardation
 Mild  irritability, motor/cognitive delays
 Chances have been reduced with fetal monitoring
 Respiratory distress syndrome
– Complicated delivery
 Forceps
 Cesarean
 Medications
Preterm and Small-for-Date
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

Postterm = born after 42 weeks