1. Human Growth and Development
Chapter Four Prenatal Development and Birth
PowerPoints prepared by Cathie Robertson, Grossmont College
Revised by Jenni Fauchier, Metropolitan Community College

3. From Zygote to Newborn Germinal period—first 14 days
Embryonic period—3rd through 8th weeks
Fetal period—9th week through birth

4. Process of Conception

5. Germinal: The First 14 Days
Zygote divides and keep dividing (at least though 3rd doubling they are the same)
At this stage (8 cells) differentiation begins
early “stem” cells take on distinct characteristics
they gravitate to locations, foreshadowing the type of cells they will become

6. Germinal: The First 14 Days, cont.
At about a week after conception the multiplying cells separate into two masses
outer layer forms a shell (later the placenta) and the inner cells from a nucleus (later the embryo)
first task of out cells to achieve implantation— embed themselves into the nuturant environment of the uterus
60% of all natural conceptions fail to implant; 70% of in vitro procedures fail to implant

7. Embryo: From the Third to the Eighth Week
First sign of human structure: thin line down the middle (22 days) that becomes the neural tube, which eventually forms the central nervous system, including brain and spinal column
fourth week
head begins to take shape
heart begins with a miniscule blood vessel that begins to pulsate

8. Embryo: From the Third to the Eighth Week, cont.
fifth week
arm and leg buds appear
tail-like appendage extends from the spine
eighth week
embryo weighs 1 gram and is 1 inch long
head more rounded; face formed
all basic organs and body parts (but for sex) present
20% of all embryos spontaneously abort now

9. Fetus: From the Ninth Week Until Birth
Called a fetus from 9th week on

10. Third Month
Sex organs take shape (Y cell sends signal to male sex organs; for females, no signal occurs)
genital organs fully shaped by 12th week
All body parts present
Fetus can move every part of body
Fetus weighs 3 ounces and is 3 inches long

11. Middle Three Months: Preparing to Survive
Heartbeat stronger
Digestive and excretory systems develop more fully
Impressive brain growth (6X in size and responsive)
new neurons develop (neurogenesis)
synapses—connections between neurons (synaptogenesis)

12. Middle Three Months: Preparing to Survive, cont.
Age of viability—age at which preterm baby can possibly survive (22 weeks)
26 weeks survival rate about 50%
brain maturation critical to viability
weight critical to viability
28 weeks survival rate about 95%

13. Fetal Brain Maturation

14. Final Three Months— Viability to Full Term
Maturation of the respiratory and cardiovascular systems
critical difference
Gains weight—4.5 lbs. in last 10 weeks

15. Risk Reduction
Despite complexity, most babies are born healthy
Most hazards are avoidable
Teratology—study of birth defects
teratogens—broad range of substances that can cause environmental insults that may cause prenatal abnormalities or later learning abilities

16. Determining Risk
Risk analysis—weighing of factors that affect likelihood of teratogen causing harm

17. Timing of Exposure
Critical period—in prenatal development, the time when a particular organ or other body part is most susceptible to teratogenic damage
entire embryonic period is critical

18. Amount of Exposure Dose and/or frequency
Threshold effect—teratogen relatively harmless until exposure reaches a certain level

19. Amount of Exposure, cont.
Interaction effect—risk of harm increases if exposure to teratogen occurs at the same time as exposure to another teratogen or risk

20. Genetic Vulnerability
Genetic susceptibilities: product of genes combined with stress
Folic-acid deficiency may cause neural- tube defects
occurs most commonly in certain ethnic groups and less often in others
Males are more genetically vulnerable

22. Specific Teratogens
No way to predict risk on an individual basis
Research has shown possible effects of most common and damaging teratogens
AIDS and alcohol extremely damaging
pregnant women with AIDS transmit it to their newborns; high doses of alcohol cause FAS; alcohol + drug use increase risk to developing organism

27. Low Birthweight less than 5 1/2 lbs.
Low Birthweight (LBW)
less than 5 1/2 lbs.
grows too slowly or weighs less than normal
more common than 10 years ago
second most common cause of neonatal death
Preterm
birth occurs 3 or more weeks before standard 38 weeks

28. maternal malnutrition
Low Birthweight, cont.
Small for Gestational Age (SGA)
maternal illness
maternal behavior
cigarette smoking (25% of SGA births)
maternal malnutrition
poorly nourished before and during pregnancy
underweight, undereating, and smoking tend to occur together

29. Low Birthweight, cont.
Factors that affect normal prenatal growth
quality of medical care, education, social support, and cultural practices

31. The Birth Process average labor for first births is 8 hours
Hormones in mother’s brain signals process
Contractions begin: strong and regular at 10 minutes apart
average labor for first births is 8 hours

32. The Birth Process

33. The Newborn’s First Minutes
Assessment—Apgar scale
five factors, 2 points each
heart rate
breathing
color
muscle tone
reflexes
score of 7 or better: normal
score under 7: needs help breathing
score under 4: needs urgent critical care

35. Variations
Parents Reaction
preparation for birth, physical and emotional support, position and size of fetus, and practices of mother’s culture
Medical Attention
birth in every developed nation has medical attention
22% of births in U.S. are cesarean section
removal of fetus via incisions in mother’s abdomen and uterus
is medical intervention always necessary?

36. Birth Complications
Cerebral Palsy—brain damage causing difficulties in muscle control, possibly affecting speech or other body movements
Anoxia—lack of oxygen that, if prolonged, can cause brain damage or death

37. First Intensive Care . . . Then Home
At the Hospital
many hospitals provide regular massage and soothing stimulation; ideally, parents share in caregiving
At Home
complications, e.g., minor medical crises
cognitive difficulties may emerge, but high-risk infants can develop normally

38. Mothers, Fathers and a Good Start
Strong family support (familia)
Fathers play a crucial role
may help wives abstain from drugs or alcohol
can reduce maternal stress
Parental alliance—commitment by both parents to cooperate in raising child
helps alleviate postpartum depression

39. Mothers, Fathers and a Good Start, cont.
Parent-infant bond—strong, loving connection that forms as parents hold, examine, and feed their newborn
immediate contact not needed for this to occur