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.