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:




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 receptors

(nervous system, skin, hair, sensory

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 4 th beat week, heart has formed and begun to

– Becomes more human in appearance during

2 nd month

– Sexual differentiation during 7 th

– 8 th 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 3 rd 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


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


Same defect

 different teratogens

One teratogen

 different defects

Some effects seen later


Age of baby

Sensitive period


Paternal influences often overlooked

– Direct and indirect effects

– Second hand smoke

– Chemicals

– Cocaine can “hitchhike”

– Smoking, alcohol, drug use

– Diets low in vitamin C sperm

Other Factors



Emotional stress

Rh blood incompatibility

Maternal/Paternal age

– Older

 less fertile, more risk of disorders

– Younger

 infant death increased risk of prematurity,

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


– Anoxia



 cerebral palsy, mental retardation irritability, motor/cognitive delays

Chances have been reduced with fetal monitoring

Respiratory distress syndrome

– Complicated delivery




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