UNIT TWO:  PRENATAL

DEVELOPMENT

Psychology 30

Concept Web

Looking through the eyes of the developing person …

Looking through the eyes of the systems of support …

Unit Objectives To understand the issues and challenges in

becoming a parent. To understand the biological changes from

conception to birth. To understand the cognitive changes from

conception to birth. To understand the socioemotional changes from

conception to birth. To understand the issues, challenges and support

systems from the perspective of microsystems, exosystems, and macrosystems of support.

2.1 Unit Overview: Human development from conception to birth Video:

National Geographic’s In The Womb

Physical Development: The germinal period is the first two weeks of

development.  This period is characterized by rapid cell division, the

beginning of cell differentiation, and implantation of the blastocyst into the uterine wall. 

By approximately one week after conception, the zygote is composed of 100 to 150 cells. 

The differentiation of cells commences and the zygote becomes differentiated into two layers:  The blastocyst is the inner layer of cells that later develop into the embryo; the trophoblast is the outer layers of cells that later provides nutrition and support for the embryo. 

Implantation of the zygote into the uterine wall takes place about 10 days after conception (Santrock, 1999, p. 103). 

Physical Development: The embryonic period is the period of prenatal

development that occurs from two to eight weeks after conception. 

The embryo's endoderm, the inner layer or cells, primarily produces internal body parts such as the respiratory and digestive systems.  T

he middle layer of cells, called the mesoderm, will become the circulatory system, bones, muscle, excretory system, and reproductive system. 

The outer layer of cells, the ectoderm, will become the nervous system, the sensory receptors (eyes, nose, ears), and skin.  As the embryo develops so too does the placenta, the umbilical cord and the amnion (fluid-filled sac) (Santrock, 1999, p. 103). 

Physical Development: The fetal period is the period of development that begins two months

after conception and lasts for seven months, on the average.  Three months after conception the fetus is 10 centimetres long and

weighs approximately 60 grams.  It has become active, moving its arms and legs, opening and closing its

mouth, and moving its head.  The face, forehead, eyelids, nose, and chin are all distinguishable, as are the

arms, hands and legs.  At four months, a growth spurt occurs in the fetus' lower parts.  By the end of the fifth month the toenails and fingernails have formed

and the fetus is more active.  By the end of the sixth month the eyes and eyelids have completely

formed, a grasping reflex is present and irregular breathing occurs.  In the last two months, fatty tissues develop and the functioning of

various organs such as the heart and kidneys steps up (Santrock, 1999, p. 103).

Cognitive Development: Some simple aspects of the functioning of the human

nervous system appear very early.  Indeed the blood circulation system and the nervous system

are the first to function in embryonic life, with heartbeat commencing in the third week following conception. 

By the second month, an avoidance reaction, the withdrawal of the hand region by contraction of the neck muscles, occurs if an unpleasant stimulus is applied to the embryonic upper lip. 

These developments imply that simple arc reflexes are already differentiated at this stage, with appropriate synaptic connections and interneuronal activity being brought into play in order to coordinate muscular movements (Rose, 1989, p. 192).

Temperament/Personality Development: Every individual is born with a distinct,

genetically-based set of psychological tendencies, or dispositions. 

These tendencies, which together are called temperament, affect and shape virtually every aspect of the individual's developing personality. 

Temperament, and therefore personality, is not merely genetic:  it begins in the multitude of genetic instructions that guide the development of the brain and then is affected by the prenatal environment (Berger, 2000, p. 219).

What are the critical periods in prenatal development?Body System Especially Sensitive Development up to …

Central nervous system/Brain

4th to 8th weeks Postnatal, through to adulthood

Heart 5th to 9th weeks 12th week

Upper limbs 6th to 10th weeks 12th week

Eyes 6th to 10 weeks Term

Lower limbs 6th to 10th weeks 12th week

Teeth 9th to 11th weeks Term

Palate 9th to 11th weeks 16th week

External genitalia 9th to 11th weeks Term

Ears 6th to 11th weeks 13th week

What are some alternative methods of conception?

In vitro fertilization (IVF):  In this procedure, ova are surgically removed from the ovaries, fertilized by sperm in the laboratory, and allowed to divide until the 16- or 32-cell stage.  The resulting cells are then inserted into the uterus, where about one cell cluster in seven successfully implants, develops and becomes a healthy baby.  The success rate is just under 20 percent (Berger, 2000, p. 73).

What are some alternative methods of conception? Gamete intrafallopian transfer (GIFT).  A

doctor inserts eggs and sperm directly into a woman’s fallopian tube.  The success rate is almost 30 percent (Santrock, 1999, p. 69).

Intrauterine (artificial) insemination.  Frozen sperm, from the husband or an unknown donor, is placed directly into the uterus, bypassing the cervix and upper vagina.  The success rate is 10 percent (Santrock, 1999, p. 69).

What are some alternative methods of conception? Zygote intrafallopian transfer.  This involves a

two-step procedure.  First, eggs are fertilized in the laboratory.  Then, any resulting zygotes are transferred to a fallopian tube.  The success rate is approximately 25 percent (Santrock, 1999, p. 69).

Intracytoplasmic sperm injection.  A doctor uses a microscopic pipette to inject a single sperm from a  man’s ejaculate into an egg.  The zygote is returned to the woman’s body.  The success rate is approximately 25 percent (Santrock, 1999, p. 69).

What are some alternative methods of conception?

Ovum donation has two possibilities:  In one version, a woman volunteers to be a surrogate mother; usually she is artificially inseminated with sperm from an infertile woman’s husband and carries the baby to term.  In another version, some of a donor woman’s ova are removed and artificially inseminated with a man’s sperm; then the cluster of cells is inserted into his own wife’s uterus (Berger, 2000, p. 73).

What are some influences that can have a negative impact on healthy prenatal development?

Harmful substances such as drugs or radiation that invade the womb and result in birth defects are called teratogens. 

Teratogens are especially damaging in the embryonic stage because it is a critical period in prenatal development. 

Later, during the fetal stage, the environment provided by the mother affects the baby’s size, behaviour, intelligence and health, rather than the formation of organs and limbs (Bernstein and Nash, 1999, p. 333).

Environment Radiation, chemicals, and other hazards in the environment

can endanger the fetus.  Chromosomal abnormalities are higher among the offspring of

fathers exposed to high levels of radiation in their occupations.  Environmental pollutants and toxic wastes are also sources of

danger to unborn children.  Among the dangerous pollutants and wastes are carbon monoxide, mercury and lead. 

Another environmental concern is toxoplasmosis, a mild infection that causes cold-like symptoms or no apparent illness in adults, but can cause eye defects, brain defects, and premature birth.  Cats are common carriers of toxoplasmosis, especially outdoor cats who eat raw meat.  The expectant mother may pick up the virus through the cat litter box (Santrock, 1999, p. 100).

Mother’s age Two time periods are of special interest: 

adolescence and the thirties and beyond.  Infants born to adolescents are often premature. 

The mortality rate of infants born to adolescent mothers is double that of infants born to mothers in their twenties. 

Down Syndrome, a form of mental retardation, is related to the mother's age.  By age 40, the probability is slightly over 1 in 100.  By age 50, it is almost 1 in 10.  The risk is also higher before age 18.  Women also have more difficulty in becoming pregnant after the age of 30 (Santrock, 1999, p. 93).

Nutrition Another common reason for slow fetal growth, and

hence low birth weight, is maternal malnutrition, a problem that has many specific causes. 

Women who begin pregnancy underweight, eat poorly during pregnancy, and consequently do not gain at least 1.5 kilograms per month in the second and third trimesters run a much higher risk than others of having a low birth weight infant. 

Indeed, women who gain less than seven kilograms, even if they are non-smokers who begin pregnancy overweight, still have a higher risk of preterm and smaller babies than those who gain at least seven kilograms (Berger, 2000, p. 119).

Infections and Diseases Maternal diseases and infections can produce defects

by crossing the placental barrier.  For example, the greatest damage to the fetus from

the mother contracting German measles occurs during the third and fourth weeks of pregnancy. 

Syphilis is more damaging later in prenatal development, four months or more after conception.  Rather than affecting organ development as Rubella does, syphilis damages organs after they have formed. 

The importance of the mother's health to the health of her offspring is nowhere better exemplified than when the mother is infected with HIV (Santrock, 1999, p. 98).

Drugs Drugs include tobacco, alcohol, prescription, or illegal drugs.  For example, the effects of thalidomide during the fourth

week of development had devastating effects.  Heavy drinking by an expectant mother can also be

devastating.  Fetal alcohol syndrome is a cluster of abnormalities that appear in the offspring of mothers who drink alcohol heavily during pregnancy.  The abnormalities include facial deformities and defective limbs, face and heart.  Most of these children are below average in intelligence.  In one study, however, even mothers who drank moderately during pregnancy had babies who were less attentive and alert, with the effects still present at four years of age. 

Drugs Cigarette smoking by pregnant women can also adversely

influence prenatal development, birth and postnatal development.  Fetal and neonatal deaths are higher among smoking mothers.  Also prevalent are a higher incidence of preterm births and lower birth weights.  Respiratory problems and sudden infant death syndrome are also more common among the offspring of mothers who smoked during pregnancy. 

Tranquilizers taken during the first three months may cause cleft palate or other congenital malformations.  Mothers who take large amounts of barbituates may have babies who are addicted or may exhibit tremors, restlessness, and irritability (Santrock, 1999, p. 98).

Poverty Compared with women of higher socioeconomic status, pregnant

women at the bottom of the economic ladder are more likely to be ill, malnourished, teenaged, and stressed. 

Physical difficulty like malfunction of the placenta or the umbilical cord is likely when pregnancies are closely spaced and close spacing correlates with poverty. 

Poverty helps explain the wide national and international variations in the following statistics: Of the more than 25 million low birth weight infants born worldwide each year

the overwhelming majority are in developing countries. Developing countries in the same geographic region, with similar ethnic

populations, have markedly different low birth weight rates when they have different average incomes.

Within nations, differences in low birth weight rates among ethnic groups follow socioeconomic differences among those groups.

Within the United States low birth weight rates in the poorest states are almost twice those in some richer states (Berger, 2000, p. 120).

Emotional state The mother's stress can be transmitted to the

fetus.  When a pregnant woman experiences intense

fears, anxieties, and other emotions, physiological changes occur in the fetus.  These include changes in respiration and glandular secretions. 

For example, producing adrenaline in response to fear restricts blood flow to the uterine area and may deprive the fetus of adequate oxygen. 

Also, reassuring the mother of fetal well-being has positive outcomes for the infants in the study (Santrock, 1999, p. 93).

What are the factors that influence the degree of affect? One crucial factor is the time at which the developing

organism is exposed to a specific teratogen.  Some teratogens cause damage only during specific

days or weeks early in pregnancy, when a particular part of the body is being formed. 

Others can be harmful at any time, but how severe the damage is depends on when the exposure occurred.  The time of greatest susceptibility is called the critical period. 

Each body structure has its own critical period.  As a general rule, for physical defects the critical period is the entire prenatal period.

What are the factors that influence the degree of affect? A second important factor is the dose and/or frequency of

exposure to a teratogen.  For most teratogens, experts are reluctant to specify a threshold below which the substance is safe.  One reason is that many teratogens have an interaction effect; that is, one poison intensifies the effects of another.

A third factor that determines whether a specific teratogen will be harmful, and to what extent, is the developing organism's genes.  In some cases, genetic vulnerability is related to the sex of the developing organism.  Generally, male embryos (XY) and fetuses are at a greater risk than female in that male embryos are more often aborted spontaneously.  In addition, newborn boys have more birth defects, and older boys have more learning disabilities and other problems caused by behavioural teratogens (Berger, 2000, pp. 106-109).