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