Developmental Psych- Chpt. 4
From Conception to Birth
-from the moment of conception, it will take approx. 266 days for the one-celled zygote to become a
-there are 3 major stages of prenatal development:
1. period of the zygote (germinal period)- lasts from conception , through implantation
(attaching to the uterus).
2. period of the embryo- lasts the beginning of the 3 week end of 8 th
-here all the major organs form and heart beat begins
3. period of the fetus- 9 weekbirth
-all major organs systems begin to function and organism grows quickly
Period of the zygote
Blastocyst- a ball shaped structure containing 60-80 cells, formed within 4days of conception
Embryo- this is what the inner layer of the blastocyst – the embryonic disk, becomes.
-outer layer of cells develops into tissues that protect and nourish the embryo
Implantation- (6-10d after conception) small tendrils appear on the surface of the blastocyst and
burrow into the uterine wall, tapping into the mother’s blood supply.
-there’s a specific “window of implantation” during which the blastocyst must communicate with the
uterine wall, position itself and invade.
-entire process completes at ~ 10-14 days after ovulation
-therefore, only ¾ zygotes fail to survive the initial phase of prenatal development
Development of Support Systems
-after implantation, blastocyst outer layer forms 4 major support structures to protect/ nourish
1. Amnion- a membrane that is a watertight sac filled with fluid from mother’s tissues (amniotic
-purpose: protect organism against blows, regulate temperature, and make it easier for
embryo to move.
-floating in here is a yolk sac that produces blood cells until embryo can make its own.
2. Chorion – yolk sac is attached to this membrane
-surrounds the amnion and becomes the lining of the:
3. Placenta (discussed later)
4. Umbilical cord- formed from the 4rth membrane, the allantois
-connects the embryo to the placenta
Purpose of the Placenta
-fed by blood vessels from the mother & embryo
-has a semipermeable barrier preventing these bloodstreams from mixing
-maternal blood flowing into the placenta delivers O₂ and nutrients into embryo bloodstream through
the umbilical cord
-umbilical cord also transports CO₂ and waste from embryo to be expelled from mother’s body Period of the Embryo
-most rapirdstage of growth
-by the 3 week the embryonic disk differentiates into 3 layers: outer layer- ectoderm (becomes the
nervous system, skin and hair); middle layer- mesoderm (muscle bones and circulatory system); inner
layer- endoderm (rdgestive system, lungs, urinary tract, pancreas, liver etc.)
Neural tube- (3 wk) formed from folding of the ectoderm and forms the brain and spinal cord
-formation of: coccyx, eyes, ears and skeleton, limbs are developing
-brain is developing rapidly and directs the organisms 1 muscular contractions
-sexual development begins and a genital ridge called the indifferent gonad appears and may or may not
receive signals from the Y chromosome to create testes.
-circulatory system functions on its own
Period of the Fetus
-last 7months of pregnancy
-organ systems function and fetus can move, sense and behave
-there is coordination b/w the nervous system and musculature to create movement
-fetus can swallow, digest and urinate
-male testes secrete testosterone
-sex of fetus can be determined
Second Trimester: 4 - 6 months
-movements might be strong enough now to be felt by the mother, heart beat is heard and skeleton
Vernix- a white cheesy substance that the fetus is now covered with to prevent from chapping
Lanugo- a fine layer of body hair that helps the vernix stick
end of 6 month fetus reacts to bright lights and sounds
Third Trimester: 7 -9 months
-growth continues and all organ systems mature in preparation for birth
Age of viability- (22-28wks) point at which survival outside the uterus is possible
-fetus’s sleep cycles and motor activity become more predictable and regular
-however, many fetuses born this young still require O₂ assistance due to tiny pulmonary alveoli.
-in last 2 weeks, fetal activity slows and sleep increases
-since fetus is now so large the most comfortable position in head down at the base of the uterus
-mother’s uterus begins to contract and relax in a process to tone the uterine muscles in preparation for
-note: the stages of development through which the developing organism passes do not correspond to
Environmental Influences on Prenatal Development
Teratogen- external agents such as viruses, drugs, chemicals and radiation that can harm a developing
embryo or fetus -95% of newborn babies are perfectly normal, and those that have defects are generally mild.
- the effects of a teratogen on a body part or organ system are worst during the period when that
structure is forming and growing most rapidly.
sensitive period- period during which an organism is quite susceptible to certain environmental
influences; these must be much stronger outside this period to have the same effects
-most vulnerable period for many organs/body parts (other than the brain and heart) is the second
-some organ systems can be damaged throughout pregnancy (ex. Eyes, genitals, nervous system)
-an embryo or fetus has an immature immune system that does not produce enough antibodies to
Rubella- has little effect on a mother but may cause a number of serious birth defects in unborn children
who are exposed in the 1 3-4 months of pregnancy (1 trimester)
-defects are commonly: blindness, deafness, cardiac abnormalities and mental retardation
Toxoplasmosis- caused by a parasite found in stw meat and cat feces; can cause birth defects if
transmitted to an embryo in the 1 trimester; can cause miscarriage later in pregnancy
-can cause severe eye and brain damage or miscarriage if strikes later in pregnancy.
-no infections are more common and few are more hazardous than the sexually transmitted diseases
Teratogenic Effects of Sexually Transmitted Diseases
Syphilis- most harmful in the middle –later stages of pregnancy b/c the microscopic organisms that
transmit the disease cannot cross the placental barrier until the 18 prenatal week.
-the disease is usually diagnosed with a blood test and treated with antibiotics
Genital herpes- can also cross the placental barrier but most infections occur at birth when the newborn
comes in contact with the lesions.
-unfortunately there is no cure, so the mother cannot be treated.
-this will kill 1/3 of infected newborns or cause blindness, brain damage or other serious
-mothers with herpes are therefore advised to undergo a caesarean section
Acquired immune deficiency syndrome (AIDS)- an incurable disease caused by the HIV virus, that
attacks the immune system and makes victims susceptible to a host of other infections that will
eventually kill them.
-the spread of HIV is through the transfer of bodily fluids (intercourse or sharing needles)
-infected mothers may pass the virus 1) prenatally, through the placenta; 2) while giving birth,
when there may be an exchange of blood b/w mother and child as the umbilical cord separates
from the placenta; and 3) after birth, if the virus is passed through the mother’s milk during
-despite all of this, less than 30% of babies born to HIV-infected mothers become infected.
-prenatal transmission can be reduced up to 70% among mothers taking the antiviral drug ZDV
-more than ½ of HIV-infected infants are living past age 6, with a fair amount surviving well into
-ZDV drug is also used to treat infected children; however they will eventually die from
The Thalidomide Tragedy- (1960) a mild over the counter tranquilizer called thalidomide that was sold
to alleviate morning sickness. -it was tested on pregnant rats and saw no ill effects on the mother or offspring
-it is now known that it is a violent teratogen for humans
-the babies born from mothers that had taken the drugs had horrible birth defects (ex.
Phocomelia- a structural abnormality in which all parts of limbs are missing and the feet or
hands may be attached directly to the torso)
-the type of birth defect depended on when the drug was taken
-heavy use of aspirin has been linked to growth retardation, poor motor control, and even infant death
-ibuprofen in the 3 trimester increases the risk of prolonged delivery and pulmonary hypertension in
-heavy use of caffeine is linked to miscarriage or low birth weight
-antidepressant drugs containing lithium can produce heart defects when taken in the 1 trimester
-medications containing sex hormones can also affect a developing embryo/fetus (ex. Birth control)
Diethylstilbestrol (DES)- synthetic sex hormone that can have serious long term effects
-was widely prescribed for the prevention of miscarriages.
-female teens whose mothers had taken DES were at risk for developing abnormalities in the
reproductive organs, including a rare cervical cancer (but 1/1000)
-daughters of mothers that had taken this drug were more likely to have a miscarriage
themselves or deliver prematurely.
-some sons of mothers that had taken DES developed minor genital abnormalities but are
-2 disorders result:
Fetal Alcohol Syndrome (FAS)- physical and neurological birth defects
-most notably results in microcephaly (small head) and malformations of the heart, limbs joints
Fetal Alcohol Effects (FES)- is the original name for a disorder now termed: Alcohol Related
Neurodevelopmental Disorder (ARND) – present when there are neurobehavioural defects in
the absence of the characteristic physical signs
-currently, these outcomes are categorized as Fetal Alcohol Spectrum Disorder (FASD)
-babies with FASD likely display excessive irritability, hyperactivity, seizures and tremors, and
have lagged physical growth.
-they also score well below average in intelligence and many display major adjustment problems
-unlike ADHD children, children with FASD display a lack of guilt after misbehaving, cruelty, a
tendency to act young for their age, and are more likely to steal and lie.
-children were more likely to display depressive symptoms
-the male reproductive system can also be affected and result in reduced sperm count, motility
and abnormally formed sperm.
-even newborns whose fathers use alcohol are likely to have lower birth weights
-behavioural screening for this early is important for early interventions
-there is no safe amount of alcohol that can be consumed during pregnancy nor a safe time period!
-3 trimester is when negative effect on fetal health is the greatest
Cleft lip- positive association b/w this and smoking during the first trimester
-may be with or without a cleft palate
-also abnormal lung function and hypertension in newborns of women who smoked -smoking is the leading cause of low birth weight and increases the risk of miscarriage
-smoking during pregnancy is also associated with higher incidences of ectopic pregancies (when the
zygote implants on the wall of the fallopian tube instead of the uterus) and sudden death of infant
-smoking may affect the regulation of autonomic activity in neonates (heartbeat more rapid as well as
presence of tremors)
-the introduction of nitcotine and CO into the fetus's bloodstream impairs the functioning of the
placenta (exchage of O₂ and nutrients)
-more cigarettes per day, the greater the chance of having a miscarriage
-children born to mothers that smoked during pregnancy or parents that smoke after they're born tend
to be smaller, more susceptible to respiratory infections and show poorer cognitive performance.
-marijuana use during pregnancy is associated with changes in functioning of the basal nucleus of the
amygdala (an area of the brain involved in the regulation of human behaviour)
-changes are more prevalent in male fetuses and may indicate that utero exposure to marijuana causes
impairment of emotional regulation
-10year old children that were exposed to marijuana once/day in utero during the 1 trimester showed
poorer performance on achievement tests for reading and spelling.
-tndse 10year olds also showed more symptoms of anxiety and depression
-2 trimester exposure was associated with reading comprehension and underachievement
-mothers that used addictive narcotics (ex. Heroin, methadone) are more likely to miscarry, delivery
prstaturely or have babies who die soon after birth
-1 month is the most difficult for a baby whose mother was addicted to a narcotic – they experience
withdrawal symptoms like vomiting, dehydration, convulsions etc.
-symptoms such as tremors, restlessness, and sleep disturbances may persist for as long as 3-4 months.
-although, some babies whose mothers were addicted to opioid drugs show normal development until
the age of 2 but it is the indifferent parenting and other such factors that is the problem
-research suggests that boys may be especially vulnerable to the effects of maternal prenatal drug abuse
-cocaine has an impact on physical and cognitive/neural development
-cocaine constricts the blood vessels of both the mother and the fetus and therefore raising blood
pressure and impairing flow of nutrients and O₂ across the placenta
-babies of cocaine (esp. Crack)-using mothers are often miscarried or premature
-they’re smaller, have lower birth weights, have smaller head circumferences, and score lower on infant
-they also experience some of the problems that heroin and methadone user’s babies do
-also, prenatal cocaine is linked to postpartum developmental deficits, like lower IQ scores, impaired
visual-spatial abilities, and problems with skills for language development
-a negative prenatal and postpartum can also influence the severity of cocaine exposure (ex. Distress)
-one study found that a majority of cocaine-exposed infants failed to establish secure emotional ties to
their primary caregivers in the 1 year.
-they also appear to show less joy from learning
-these are another class of teratogens Radiation-
-not 1 pregnant women who was within 0.8km of the atomic blasts in Japan (1945) gave birth to a live
-no one knows how much radiation it takes to harm an embryo or fetus
-pregnant women are therefore advised to avoid x-rays (of the pelvis and abdomen in particular)
Chemicals and Pollutants-
-includes organic dyes and colouring agents, food additives, artificial sweeteners, pesticides and
-there are also pollutants in the air we breathe and water we drink lead, zinc, mercury or antimony (in
house paints or water pipes)
-these “heavy metals” are known to impair the physical health & mental abilities of adults and children
and to have teratogenic effects (produce physical deformities & mental retardation) in developing
embryos and fetuses.
-PCBs (polychlorinated biphenyls) once widely used in plastics and carbon paper (though now outlawed)
presented another hazard
-even mothers that had eaten PCB contaminated fish had smaller than average newborns and less
neurologically mature babies
-depending on the dose, they also scored lower on tests of short term memory and verbal reasoning
-prenatal PCB exposure has also been linked to difficulty maintaining attention and slower reaction
-these effects may occur with lactational exposure to PCBs post birth
-even a father’s exposure to environmental toxins can affect children
such as radiation, anesthetic gases, and other toxic chemicals can damage a father’s
chromosomes, increasing the likelihood of his child being miscarried.
-even when pregnant mothers don’t drink or use drugs, they are more likely to deliver a low-birth-
weight baby or one with other defects if the father drinks or uses drugs
-this may be b/c these toxins can bind to live sperm and cause mutations
-therefore.... 1) environmental toxins can affect the reproductive system of either parent so that
(2) both mothers and fathers should limit their exposure to substances to known teratogens
The Mother’s Diet
-currently, pregnant women are advists to eat a healthy, high protein, high calorie diet on which they
gain about 1.0-2.0kg during the 1 3 months and about 0.5kg a week thereafter, for a total increase of
-malnutrition in the 1 trimester – can disrupt the formation of the spinal cord & induce miscarriage
-malnutrition in tst 3 trimester – likely results in low-birth weight babies with small heads who may fail
to survive their 1 year
-they also tend to have lower brain weights and therefore show cognitive deficits
-dietary supplements and stimulating daycare can decrease the potentially damaging long-term effects
of prenatal malnutrition
- poor women are at risk of poor nutrition, therefore in Canada there are supplement programs in some
-note: pregnant women who have plenty to eat may still fail to obtain all of the vitamins and minerals -magnesium and zinc in the diet improves the functioning of the placenta & reduces the incidence of
-iodine ensures normal thyroid functioning – a deficiency could cause congenital hypothyroidism known
as cretinism, which leads to irreversible mental retardation
Folic acid- a B-complex vitamin (in fruit, beans, liver, tuna and green veggies) helps to prevent Down
Syndrome, spina bifida and anencephaly (especially important in 1 8weeks of pregnancy)
Spina bifida- a bulging of the spinal cord through a gap in the spinal column
Anencephaly- a birth defect in which the brain and neural tube fail to develop or develop incompletely
and the skull does not close
-most women do not consume enough folic acid and new campaigns are trying to ensure that women of
child bearing ages are provided with at least 0.4mg/day
-however, more is not better – can result in too much vitamin A and cause birth defects
Mother’s Emotional Well Being
-when a mother is emotionally aroused and releases hormones like adrenaline, they can pass the
placental barrier, reach the fetuses blood stream and increase its motor activity
-temporary stressful situations for a mother have few if any harmful effects on a fetus
-prolonged severe emotional stress is associated with stunted prenatal growth, premature delivery, low
birth weight, decreased fetal motor activity and other birth complications
-stress-induced changes in the fetus may be caused by the sensory experience the fetus has, in addition
to the changes in heart rate and hormones crossing the placenta
-babies of highly stressed women tend to be highly active, irritable, and have irregular feeding, sleeping
and bowel habits.
-long term consequences of maternal stress appear to be linked with a sensitive period during gestation
(12-22 weeks of gestation)
-these include: increased for development of ADHD, externalizing problems (ex. Temper tantrums), and
-stress hormones divert blood flow to the large muscles and impede the flow of O₂ and nutrients to the
-stress may also weaken a pregnant women’s immune system
-stressed mothers may also be more likely to eat poorly, smoke, or use drugs or alcohol
-it does seem however, that the presence of stressors in a woman’s life is far less important than her
ability to manage such stress
-stress related complications are more likely when pregnant women 1) are ambivalent or negative about
their marriages or their pregnancies and (2) have no friends or other bases of social support to turn to