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Chapter 3:
Prenatal Development and Birth
In This Chapter
Conception and GeneticsChromosomes, DNA, and Genes
Process of conception Ovum Sperm Zygote
Chromosomes DNA Genes
Conception and GeneticsSex Determination
Chromosomes Autosomes Sex chromosomes (X, Y)
Chromosomal differences Androgens and SRY gene Sex chromosomes (X, Y) Gonad development
Conception and GeneticsMultiple Births
Twins• Identical (monozygotic)
• Fraternal (dizygotic)
• Semi-identical (different genes from father)
Stop and Think!
Your textbook notes an increase in multiple births over the past thirty years.
Why has this occurred?
Conception and GeneticsHow Genes Influence Development
Genotype: Genetic blueprint
Phenotype: Observable characteristics
Dominant–recessive pattern
Polygenic inheritance
Let’s Take a Look…
Whose hair do you have?
On the next slide you will see the genetics of hair type. Did you answer the above question correctly?
The Genetics of Hair Type
Conception and GeneticsOther Types of Inheritance
Genomic imprinting: Some genes biochemically marked at time ova and sperm develop
Mitochondrial inheritance: Genes in mitochondria
Conception and GeneticsMulti-Factorial Inheritance (MFI)
MFI: Inheritance affected by genes and environment
Five general principles (Rutter et al.)
In what ways have genetics and environment integrated to influence your
development?
Genetic DisordersAutosomal Disorders
Autosomal gene: One of 22 pairs of autosomes that are involved in sex determination
Autosomal recessive disorder: 2 copies of the abnormal gene must be present for the disease or trait to develop.
Autosomal dominant disorder: abnormal gene from 1 parent sufficient to inherit disease or trait
See Table 3.2 for a summary of some genetic disorders.
Genetic DisordersSex-Linked Disorders
Sex-linked disorders: Caused by recessive gene on X chromosome
Stop and Think…
Why do boys have Fragile X Syndrome more often than girls?
Chromosomal ErrorsTrisomies and Monosomies
Trisomies: Three chromosomes, rather than usual pair
Monosomies: Absence of one member of chromosome pair
Chromosomal ErrorsSex Chromosome Anomalies
Trisomy 21: Down syndrome
XXY: Klinefelter’s syndrome
XO: Turner’s syndrome
XXX: girls with an extra X
XYY: boys with an extra Y
Pregnancy and Prenatal Development
The Mother’s Experience: First Trimester
Care• Regular prenatal care critical at this time
Problems• Ectopic pregnancy, bleeding, miscarriage
Pregnancy and Prenatal Development
The Mother’s Experience: Second Trimester
Care Monthly doctor visits continue Ultrasound
Problems Gestational diabetes; Rh incompatibility;
increased blood pressure Miscarriage; premature labor
Pregnancy and Prenatal Development
The Mother’s Experience: Third Trimester
Care• Weekly visits (beginning in 32nd week)• Ultrasound to assess position, pelvic exam to check
cervical dilation
Problems Increased blood pressure, bleeding, bladder
infection Premature labor
Pregnancy and Prenatal Development
The Prenatal Experience: Germinal Stage
Conception to implantation
Blastocyst implants
Specialization of cells needed to support development
Pregnancy and Prenatal Development
The Prenatal Experience: Embryonic Stage
2 to 8 weeks after conception
Neural tube develops
Forms foundations of all body organs and systems
Many organs and systems begin to function.
Pregnancy and Prenatal Development
The Prenatal Experience: Fetal Stage
End of week 8 until birth
Growth from 1/4 ounce and 1 inch to 7 pounds and 20 inches in length
Refinement of all organ systems
Neuronal proliferation
Viable at Week 24; full-term at Week 37
Figure 3.3: Parts of the Neuron
Structure of a Single Neuron
• Cell bodies first to develop (wks 12-24)
• Axons and dendrites develop later (especially final 12 wks).
• Axons continue to increase in size and complexity after birth.
Figure 3.3. Parts of the Neuron
Prenatal Sex Differences
Males More physically active Higher rates of miscarriage More vulnerable to prenatal problems
Females More sensitive to external stimulation More rapid skeletal development
Prenatal Sex DifferencesSome researchers suggest:
Males More physically active More vulnerable to
prenatal problems
Females More sensitive to
external stimulation More rapid skeletal
development
Other researchers contend:
Sex differences in:• Prenatal hormones
linked to cross-gender variations
• Prenatal problems
Can you guess what these might be?
Prenatal BehaviorIntroducing the Amazing Fetus!
Fetuses can differentiate between familiar and novel stimuli by 32 to 33 weeks.
Newborns can remember prenatal stimuli and react accordingly.
Very active fetuses tend to be active children who can be labeled “hyperactive” later on.
Figure 3.6 Correlations between Fetal Behavior and Brain Development
You are told by a genetic counselor that you have 25 percent chance of passing on a deadly genetic trait to your child. Do you still have a child? What factors influence your choice?
How do we curtail the use of teratogens, such as smoking and alcohol use, by pregnant women?
Questions To PonderQuestions To PonderQuestions To PonderQuestions To Ponder
Teratogen: substance that can
damage embryo
Teratogen: substance that can
damage embryo
See Figure 3.7 for timing of exposure
Greatest damage during organ
system’s most rapid development
First 8 weeks m
ost
dangerous
exposure time
Dura
tion
and
inte
nsity
exp
osur
e important
Problems in Prenatal DevelopmentTeratogens
Figure 3.7 Timing of Teratogen Exposure
Problems in Prenatal DevelopmentTeratogens: Drugs
Prescription Over-the-counter drugs Marijuana, methamphetamine, and heroin Cocaine Tobacco Alcohol
Problems in Prenatal DevelopmentTeratogens: Maternal Diseases
Rubella (“German measles”) HIV Other sexually transmitted diseases
Problems in Prenatal DevelopmentOther Maternal Influences: Diet
Folic acid deficiencies
Malnutrition Neonate low birth weight Brain stunting Fetal death Mental illness in adulthood
Problems in Prenatal DevelopmentOther Maternal Influences: Age
First pregnancies are occurring later—average age is now 25.1 years.
Women over 35 have higher risks for pregnancy complications.
Teenage mothers have higher risks during and after birth.
Problems in Prenatal DevelopmentOther Maternal Influences: Chronic Illnesses
Kinds of illness Depression Epilepsy Diabetes Lupus
Prevention Monitoring of mother and fetus necessary for
most illnesses Fetal–maternal specialist for high-risk patient
Problems in Prenatal DevelopmentEnvironmental Hazards
Detrimental effects of hazards may be reduced by:
Limiting exposure to lead and mercury
Avoiding possible harmful chemicals
Problems in Prenatal DevelopmentMaternal Emotions
Maternal stress and depression related to higher risks for fetus
Social support and counseling may help.
Mixed information from research
Fetal Assessment and Treatment
Can you identify each method?
Figure 3.8 Two Methods of Prenatal Diagnosis
Stop and Think!
With the advent of antiretroviral drugs, the rate of mother-to-fetus transmission has been greatly reduced.
Do these findings justify mandatory testing and treatment of pregnant women who are at high risk of having HIV/AIDS?
Birth and the NeonateBirth Choices
Things to consider Location of birth
Birth attendants
Drugs during labor and delivery
“Natural childbirth”
Want to make a birth plan?
How would you plan the ideal birth for yourself, a partner, or a friend?
Go to the link below to develop your birth plan.
Did you include everything in your above ideal plan?
http://www.childbirth.org/interactive/ibirthplan.html
The Physical Process of BirthLabor: An Overview
Stage 1 Contractions Dilation of the cervix
Stage 2 Actual delivery of the baby
Stage 3 Delivery of the placenta and umbilical
cord
Figure 3.9 The Three Stages of Labor
Figure 3.9 The Three Stages of Labor
The Physical Process of BirthBirth Complications: Cesarean Deliveries
Why are Cesarean deliveries performed? Fetal distress Breech presentation Birth size Poor progress during labor Mother’s health and age concerns
The Physical Process of BirthAssessing the Neonate
Apgar scale
Brazelton Neonatal Behavioral Assessment
Why is neonatal assessment important?
Assessing the NeonateLow Birth Weight Babies (LBW)
LBW: below 2,500 grams (5.5 pounds)
Preterm: mostly born before Week 38
Small-for-date neonates
Risks
Respiratory distress syndrome
Intervention
Adequate parental education and support reduces risk of complications.
Assessing the NeonateDo LBW babies catch up?
Development best assessed on individual basis
Two-thirds to three-fourths of preterm infants catch up by school entrance.
Lowest birth weight and earlier gestational age associated with long-term developmental delays.