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 4 th week, heart has formed and begun to beat
– 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

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