Each one of us is made up of trillions of units called cells. Every cell contains a rodlike structures called chromosomes, which store and transmit genetic information. Chromosomes are made up of a chemical substance called deoxyribonucleic or DNA. A unique feature of DNA is that it can duplicate itself through a process called mitosis.
New individuals are created when two special cells called gametes, or sex cells - the sperm and ovum - combine.
A gamete contains only 23 chromosomes, half as many as a regular body cell. Gametes are formed through cell division process called meiosis,
which halves the number of chromosomes normally present in body cells. When sperm and ovum unite at conception the resulting cell, called zygote,
will again have 46 chromosomes. A special event called crossing over occurs, in which chromosomes next to each other break at one or more points
along their length and exchange segments, so that genes from one are replaced by genes from another.
The 22 matching pairs of chromosomes, which geneticists number from longest (1) to shortest (22). These are called autosomes. The twenty third pair consists of sex chromosomes. In females, this pair is called XX; in males, it is called XY.
sex of the baby is determined by a sex chromosome that is carried in
sperm. When a sperm carrying an X chromosome fertilizes an egg, a female
offspring is conceived. When a sperm carries a Y chromosome, a male is
conceived. The Y sperm contains slightly less genetic maternal than
X-chromosome sperm. Y sperm are slightly lighter, travel faster and may
be more fragile than X-chromosome sperm.
In the past, many couples with genetics disorders in their families chose not to bear a child at all than than risk the birth with abnormalities. Today, genetics counseling and prenatal diagnosis help people make informed decisions about conceiving, carrying a pregnancy to term, or adopting a child.
Genetic counseling is a communication process designed to help couples assess their chances of giving birth to a baby with a hereditary disorder and choose the best course of action in view of risks and family goals.Any person may seek out genetic counseling for a condition they may have inherited from their biological parents.
A woman, if pregnant, may be referred for genetic counseling if a risk is discovered through Prenatal testing (screening or diagnosis). Some clients are notified of having a higher individual risk for chromosomal abnormalities or birth defects. Testing enables women and couples to make a decision as to whether or
not to continue with their pregnancy, and helps provide information that
can be used to prepare for the birth of a child with medical issues.
A person may also undergo genetic counseling after the birth of a
child with a genetic condition. In these instances, the genetic
counselor explains the condition to the patient along with recurrence
risks in future children. In all cases of a positive family history for a
condition, the genetic counselor can evaluate risks, recurrence and
explain the condition itself.
Families or individuals may choose to attend counseling or undergo prenatal testing for a number of reasons.
- Family history of a genetic condition or chromosome abnormality
- Molecular test for single gene disorder
- Increased maternal age (>30-35 years)
- Increased paternal age (>30-35 years)
Prenatal Diagnosis and Fetal Medicine
If couples who might bear a child with abnormalities decide to conceive, several prenatal diagnostic methods - medical procedures that permit detection of developmental problems before birth - are available.
Specifically, prenatal diagnosis is helpful for:
- Managing the remaining weeks of the pregnancy
- Determining the outcome of the pregnancy
- Planning for possible complications with the birth process
- Planning for problems that may occur in the newborn infant
- Deciding whether to continue the pregnancy
- Finding conditions that may affect future pregnancies
The techniques employed for
prenatal diagnosis include:
- Amniocentesis:- This is an invasive procedure in which a needle is passed through the
mother's lower abdomen into the amniotic cavity inside the uterus. Enough
amniotic fluid is present for this to be accomplished starting about 14 weeks
gestation. For prenatal diagnosis, most amniocenteses are performed between 14
and 20 weeks gestation.
- Chorionic villus sampling:- In this procedure, a catheter is passed via the vagina through the cervix
and into the uterus to the developing placenta under ultrasound guidance.
Alternative approaches are transvaginal and transabdominal. The introduction of
the catheter allows sampling of cells from the placental chorionic villi. These
cells can then be analyzed by a variety of techniques. The most common test
employed on cells obtained by CVS is chromosome analysis to determine the
karyotype of the fetus. The cells can also be grown in culture for biochemical
or molecular biologic analysis. CVS can be safely performed between 9.5 and
12.5 weeks gestation.
Prenatal diagnosis has led to advances in fetal medicine. For example, by inserting a needle into the uterus, doctors can administer drugs to the fetus. Surgery has been performed to repair such problems as heart, lungs etc.
These techniques frequently result in complications, the most common being premature labor and miscarriage.
The Pros and Cons of Reproductive Technologies
Some couples decide not to risk pregnancy due the history of genetic disease. Many others - in fact 1/6th of all couples who try to conceive - discover that they are infertile. And some never married adults and gay and lesbian partners want to bear children, There are many alternative methods of conception - technologies available that fulfill the wish of parenthood.
Donor Insemination: Injection of sperm from an anonymous man into a woman - to overcome male reproductive difficulties. This procedure is an increasingly popular option for lesbian and gay couples who would like to start a family. Some women prefer using a donor from a sperm bank to ensure that the donor has no interest in the child's life. The
donors are usually anonymous, and their sperm is screened to ensure that
they are virile and healthy. On the other hand Some women opt to use the sperm from a close friend, or conduct
interviews with interested men to find the right sperm donor. This gives
them an opportunity to gain greater knowledge about the donors'
personality and family history. There
are certain pitfalls associated with using a known donor, however. For
one, unless you have an attorney create a contract, issues surrounding
parental rights can cause problems down the line. You will have to agree
with your potential donor ahead of time issues such as how much he will
be involved in the child’s life and whether or not he will have any
financial obligations towards your child. The simple act of hiring an
attorney could easily offset whatever you will save by not having to pay
for the sperm.
In Vitro Fertilization (IVF): Is a process by which egg cells are fertilized by sperm outside the body: in vitro. IVF is a major treatment in infertility when other methods of assited reproductive technology have failed. The process involves hormonally controlling the ovulatory process, removing ova (eggs) from the woman's ovaries and letting sperm fertilise them in a fluid medium. The fertilised egg (zygote) is then transferred to the patient's uterus with the intent to establish a successful pregnancy. Possible risks may occur throughout the procedure, but the risk you may
encounter depend on the specific step of the procedure. During ovarian
stimulation, hyperstimulation syndrome may occur. This results in
swollen, painful ovaries and some form of it (mild, moderate or severe)
occurs in 30% of patients. Mild cases can be treated with over the
counter medications and cases can be resolved in the absence of
pregnancy. In moderate cases, ovaries swell and fluid accumulated in the
abdominal cavities and may have symptoms of heartburn, gas, nausea or
loss of appetite. In severe cases patients have sudden excess abdominal
pain, nausea, vomiting and will result in hospitalisation. During egg
retrieval, there’s a small chance of bleeding, infection, and damage to
surrounding structures like bowel and bladder (transvaginal ultrasound
aspiration) as well as difficulty breathing, chest infection, allergic
reactions to meds, or nerve damage (laproscopy). During embryo transfer,
if more than one embryo is transferred there’s always a risk of
multiple pregnancy, infertile couples may see this is good news but
there may be risk to the embryos and to the mother such as premature
Surrogate motherhood: Is an arrangement in which a woman carries and delivers a child for
another couple or person. This woman, the surrogate mother, may be the
child's genetic mother (called traditional surrogacy), or she may be biologically unrelated to the child (called gestational surrogacy). In a traditional surrogacy the child may be conceived via home artificial insemination using fresh or frozen sperm or impregnated via IUI (intrauterine insemination), or ICI (intracervical insemination) performed at a health clinic. Because
gestational surrogacy requires the implantation of a previously created
embryo, that process always takes place in a clinical setting. No matter how professionally a surrogate mother views her arrangement
with the couple for whom she is carrying a child, emotional attachments
to the child are always a risk. A surrogate must be emotionally prepared
to deal with these feelings while honoring her contract. If you have
any reservations about your ability to relinquish a child you have
carried for another couple, surrogacy is not for you. There are risks involved for both parties in a surrogacy contract. The
surrogate mother runs the risk of experiencing complications related to
pregnancy that may have a negative effect on her health. The expectant
couple runs the risk of disappointment if the pregnancy fails or if the
child is born with a defect. Just like any pregnancy, there is no
guarantee of a happy, healthy outcome.
The Alternative of Adoption
Adults who are infertile, who are likely to pass along a genetic disorder, or who are older and single want a family are turning to adoption in increasing numbers. Those who have children by birth, too, sometimes choose to expand their families through adoption.
Adoption is a process whereby a person assumes the parenting for another and, in so doing, permanently transfers all rights and responsibilities from the original parent or parents. Unlike guardianship or other systems designed for the care of the young, adoption is
intended to effect a permanent change in status and as such requires societal recognition, either through legal or religious sanction. Historically some societies have enacted specific laws
governing adoption whereas others have endeavored to achieve adoption
through less formal means, notably via contracts that specified inheritance rights and parental responsibilities. Modern systems of adoption, arising in the 20th century, tend to be governed by comprehensive statutes and regulations.
Adopted children and adolescents - whether or not they are born in their adoptive parents country - tend to have more learning and emotional difficulties than other children, a difference that increases with the child's age at time of adoption. There are many possible reasons for adoptees' more problematic childhoods. The biological mother may have been unable to care for the child because of problems believed to be partly genetic, such as alcoholism or severe depression, and may have passed this tendency to her offspring. Or perhaps she experienced stress, poor diet, or inadequate medical care during Pregnancy. Despite these risks, most adopted children fare well, and those with preexisting problems usually make rapid progress.
Relationship between Heredity and Environment
Have you ever wondered why people resemble their parents?
The answer to this and other questions about inheritance lies in a
specialized branch of biology called genetics.
Geneticist found that most aspects of life have a hereditary basis and
that many traits can appear in more than one form. For instance, human
beings have blond, or red, or brown, or black hair. They may have one of
several different types of blood, one or several colors of skin. Their
ear lobes may be attached or free. They may or may not be able to
manufacture certain enzymes. Some of these traits are much more
important to the life of the individual than others, but all of them are
hereditary. The geneticist is interested not only in the traits of man
but in those of all other organisms as well.
The study of inheritance depends on the
differences as well as the similarities between parents and offspring over
Heredity is very complex, and a geneticist
cannot possibly analyze all the traits of an organism at once. Instead, he
studies only a few traits at a time. Many other traits are present. As the
geneticists work out the solution to each hereditary mystery, the geneticist
must not forget that all organisms live in a complex environment. The
environment may affect the degree to which a hereditary trait develops. The
geneticist must try to find out which of the many parts of the environment may
affect his results.
The factors must be kept as constant as
possible by using controlled experiments. Only then can he tell that the
differences observed are due to heredity.
Heredity determines what an organism may
become, not what it will become. What an organism becomes depends on both its
heredity and environment.
The concept of heritability plays a central role in
the psychology of individual differences. Heritability has two
definitions. The first is a statistical definition, and it defines
heritability as the proportion of phenotypic variance attributable to genetic variance. The second definition is more common "sensical". It defines heritability as the extent to which genetic individual differences contribute to individual differences in observed behavior (or phenotypic individual differences). You should memorize both of these definitions.
Because heritability is a proportion, its numerical value will range
from 0.0 (genes do not contribute at all to phenotypic individual
differences) to 1.0 (genes are the only reason for individual
differences). For human behavior, almost all estimates of heritability
are in the moderate range of .30 to .60.
The quantity (1.0 - heritability) gives the environmentability
of the trait. Environmentability has an analogous interpretation to
heritability. It is the proportion of phenotypic variance attributable
to environmental variance or the extent to which individual differences
in the environment contribute to individual differences in behavior. If
the heritability of most human behaviors is in the range of .30 to .60,
then the environmentability of most human behaviors will be in the range
of .40 to .70.
There are five important attributes about estimates of heritability and environmentability. They are:
- Heritability and environmentability are abstract concepts. No
matter what the numbers are, heritability estimates tell us nothing
about the specific genes that contribute to a trait. Similarly, a
numerical estimate of environmentability provides no information about
the important environmental variables that influence a behavior.
- Heritability and environmentability are population concepts.
They tell us nothing about an individual. A heritability of .40 informs
us that, on average, about 40% of the individual differences that we
observe in, say, shyness may in some way be attributable to genetic
individual difference. It does NOT mean that 40% of any person's shyness is due to his/her genes and the other 60% is due to his/her environment.
- Heritability depends on the range of typical environments in the population that is studied.
If the environment of the population is fairly uniform, then
heritability may be high, but if the range of environmental differences
is very large, then heritability may be low. In different words, if
everyone is treated the same environmentally, then any differences that
we observe will largely be due to genes; heritability will be large in
this case. However, if the environment treats people very differently,
then heritability may be small.
- Environmentability depends on the range of genotypes in the population studied.
This is the converse of the point made above. However, it probably does
not apply strongly to human behavior as it does to the behavior of
specially bred animals. Few--if any--human populations are as
genetically homogeneous as breeds of dogs, sheep, etc.
- Heritability is no cause for therapeutic nihilism. Because heritability depends on the range of typical environments in the population studied, it tells us little about the extreme environmental interventions utilized in some therapies.
Genetic Environmental Correlation
Gene-environment correlations can arise by both causal and non-causal mechanisms. Of principal interest are those causal mechanisms, which indicate
genetic control over environmental exposure. Genetic variants influence
environmental exposure indirectly via behavior. Three causal mechanisms
giving rise to gene-environment correlations have been described.
- (i) Passive gene-environment correlation refers to the
association between the genotype a child inherits from her parents and
the environment in which the child is raised. Parents create a home
environment that is influenced by their own heritable characteristics. Biological parents also pass on genetic material to
their children. When the children's genotype also influences their
behavioral or cognitive outcomes, the result can be a spurious relationship between environment and outcome. For example, because parents who have
histories of antisocial behavior (which is moderately heritable) are at
elevated risk of abusing their children, a case can be made for saying
that maltreatment may be a marker for genetic risk that parents transmit
to children rather than a causal risk factor for children’s conduct
- (ii) Evocative (or reactive) gene-environment correlation
happens when an individual's (heritable) behavior evokes an
environmental response. For example, the association between marital
conflict and depression may reflect the tensions that arise when
engaging with a depressed spouse rather than a causal effect of marital
conflict on risk for depression.
- (iii) Active gene-environment correlation occurs when an
individual possesses a heritable propensity to select environmental
exposure. For example, individuals who are characteristically
extroverted may seek out very different social environments than those
who are shy and withdrawn.
Gene-environment correlation can also arise from non-causal
mechanisms, including evolutionary processes and behavioral
'contamination' of the environmental measure. Evolutionary processes,
such as genetic drift and natural selection,
can cause allele frequencies to differ between populations. For
example, exposure to malaria-bearing mosquitoes over many generations
may have caused the higher allele frequency among certain ethnic groups
for the sickle hemoglobin (HbS) allele, a recessive mutation that causes sickle-cell disease but confers resistance against malaria. In this way, HbS genotype has become associated with the malarial environment.
Researchers call this view of the relationship between heredity and environment the epigenetic framework. Epigenesis means development resulting from ongoing, bidirectional exchanges between heredity and all levels of the environment.
Advantages and Disadvantages of Parenthood Mentioned by American Couples
| Giving and receiving warmth and affection|| Loss of freedom, being tied down|
| Experiencing the stimulation and fun that children add to life|| Financial strain|
| Being accepted as a responsible and mature member of the community|| Family–work conflict—not enough time to meet both child-rearing and job responsibilities|
| Experiencing new growth and learning opportunities that add meaning to life|| Interference with mother’s employment opportunities and career progress|
| Having someone to provide care in old age|| Worries over children’s health, safety, and well-being|
| Gaining a sense of accomplishment and creativity from helping children grow|| Risks of bringing up children in a world plagued by crime, war, and pollution|
| Learning to become less selfish and to sacrifice|| Reduced time to spend with husband or wife|
| Having someone carry on after one’s own death|| Loss of privacy|
| Having offspring who help with parents’ work or add their own income to the family’s resources|| Fear that children will turn out badly, through no fault of one’s own|
Currently, it is 1.8 in the United States; 1.7 in Australia, Great Britain, and Sweden; 1.6 in Canada; 1.4 in Japan and Germany; and 1.3 in Italy (U.S. Census Bureau, 2007a; 2007b). In addition to more effective birth control, a major reason for this decline is that a family size of one or two children is more compatible with a woman’s decision to divide her energies between family and work. Marital instability has also contributed to smaller families: More couples today get divorced before their childbearing plans are complete. Popular advice to prospective parents often recommends limiting family size in the interests of “child quality”— more parental affection, attention, and material resources per child, which enhance children’s intellectual development. Do large families make less intelligent children, as prevailing attitudes suggest? Or do less intelligent parents—as a result of heredity, environment, or both— tend to have larger families? To find out researchers turned to a large, two-generation longitudinal study.
Although many good reasons exist for limiting family size, the concern that additional births will reduce children’s intelligence and life chances is not warranted. Rather, young people with lower mental test scores—many of whom dropped out of school, live in poverty, lack hope for their future, and fail to engage in family planning—are most likely to have large families. Both are vital for improving children’s quality of life.
Childbearing AgeMany people believe that women should, ideally, give birth in their twenties, not only because the risk of having a baby with a chromosomal disorder increases with age but also because younger parents have more energy to keep up with active children. However, first births to women in their thirties have increased greatly over the past quarter century. Many people are delaying childbearing until their education is complete, their careers are established, and they know they can support a child. Older arents may be somewhat less energetic than they once were, but they are financially better off and emotionally more mature. For these reasons, they may be better able to invest in parenting. Nevertheless, reproductive capacity does decline with age. Fertility problems among women increase from age 15 to 50, with a sharp rise in the mid-thirties. Between ages 25 and 34, nearly 14 percent of women are affected, a figure that climbs to 26 percent for 35- to 44-year-olds. Age also affects male reproductive capacity. Amount of semen and concentration of sperm in each ejaculation gradually decline after age 30. Consequently, compared to a 25-year old man, a 45-year-old is 12 times as likely to take more than two years to achieve a conception.
Stages of Prenatal Development
The process of prenatal development occurs in three main stages. The
first two weeks after conception are known as the germinal stage; the
third through the eighth week are known as the embryonic period; and the
time from the ninth week until birth is known as the fetal period.
The Germinal Stage
The germinal stage begins with conception, when the sperm and egg
cell unite in one of the two fallopian tubes. The fertilized egg, known
as a zygote,
then moves toward the uterus, a journey that can take up to a week to
complete. Cell division begins approximately 24 to 36 hours after
Within just a few hours after conception, the singe-celled zygote
begins making a journey down the fallopian tube to the uterus where it
will begin the process of cell division and growth. The zygote first
divides into two cells, then into four, eight, sixteen, and so on. Once
the eight cell point has been reached, the cells begin to differentiate
and take on certain characteristics that will determine the type of
cells they will eventually become. As the cells multiply, they will also
separate into two distinctive masses: the outer cells will eventually
become the placenta while the inner cells will form the embryo.
Cell division continues at a rapid rate and the cells then develop into what is known as a blastocyst. The blastocyst is made up of three laters:
- The ectoderm (which will become the skin and nervous system)
- The endoderm (which will become the digestive and respiratory systems)
- The mesoderm (which will become the muscle and skeletal systems).
Finally, the blastocyst arrives at the uterus and attached to the uterine wall, a process known as implantation.
Implantation occurs when the cells nestle into the uterine lining and
rupture tiny blood vessels. The connective web of blood vessels and
membranes that forms between them will provide nourishment for the
developing being for the next nine months. Implantation is not always an
automatic and sure-fire process. Researchers estimate that
approximately 58 percent of all natural conceptions never become
properly implanted in the uterus, which results in the new life ending
before the mother is ever aware she is pregnant.
When implantation is successful, hormonal changes halt a woman’s
normal menstrual cycle and cause a whole host of physical changes. For
some women, activities they previously enjoyed such as smoking and
drinking alcohol or coffee may become less palatable, possibly part of
nature’s way of protecting the growing life inside her.
The Embryonic Stage
The mass of cells is now know as and embryo. The beginning of
the third week after conception marks the start of the embryonic period,
a time when the mass of cells becomes a distinct human being. The
embryo begins to divide into three layers each of which will become an
important body system. Approximately 22 days after conception, the
neural tube forms. This tube will later develop into the central nervous
system including the spinal cord and brain.
Around the fourth week, the head begins to form quickly followed by
the eyes, nose, ears, and mouth. The cardiovascular system is where the
earliest activity begins as the blood vessel that will become the heart
start to pulse. During the fifth week, buds that will form the arms and
By the time the eight week of development has been reached, the
embryo has all of the basic organs and parts except those of the sex
organs. It even has knees and elbows! At this point, the embryo weight
just one gram and is about one inch in length.
The Fetal Stage
Once cell differentiation is mostly complete, the embryo enters the next stage and becomes known as a fetus.
This period of develop begins during the ninth week and lasts until
birth. The early body systems and structures established in the
embryonic stage continue to develop. The neural tube develops into the
brain and spinal cord and neurons form. Sex organs begin to appear
during the third month of gestation. The fetus continues to grow in both
weight and length, although the majority of the physical growth occurs
in the later stages of pregnancy.
This stage of prenatal development lasts the longest and is marked by
amazing change and growth. During the third month of gestation, the sex
organs begin to differentiate and by the end of the month all parts of
the body will be formed. At this point, the fetus weight around three
The end of the third month also marks the end of the first trimester
of pregnancy. During the second trimester, or months four through six,
the heartbeat grows stronger and other body systems become further
developed. Fingernails, hair, eyelashes and toenails form. Perhaps most
noticeably, the fetus increases quite dramatically in size, increasing
about six times in size. The brain and central nervous system also
become responsive during the second trimester. Around 28 weeks, the
brain starts to mature much faster with activity that greatly resembles
that of a sleeping newborn.
During period from seven months until birth, the fetus continues to
develop, put on weight, and prepare for life outside the womb. The lungs
begin to expand and contract, preparing the muscles for breathing.
Prenatal Environmental Influences
Although the prenatal environment is far more constant than the world outside the womb, a great many factors can affect the embryo and fetus. Let’s look at some factors that can influence the prenatal environment.
The term teratogen refers to any environmental agent that causes damage during the prenatal period. It comes from the Greek word teras, meaning “malformation” or “monstrosity.” Scientists selected this label because they first learned about harmful prenatal influences from cases in which babies had been profoundly damaged. But the harm done by teratogens is not always simple and straightforward. It depends on the following factors:
■ Dose. As we discuss particular teratogens, we will see that larger doses over longer time periods usually have more negative effects.
■ Heredity. The genetic makeup of the mother and the developing organism plays an important role. Some individuals are better able than others to with stand harmful environments.
■ Other negative influences. The presence of several negative factors at once, such as poor nutrition, lack of medical care, and additional teratogens, can worsen the impact of a single harmful agent.
■ Age. The effects of teratogens vary with the age of the organism at time of exposure.We can best understand this last idea if we again think of the sensitive period concept. Recall that a sensitive period is a limited time span in which a part of the body or a behavior is biologically prepared to develop rapidly. During that time, it is especially sensitive to its surroundings. If the environment is harmful, then damage occurs, and recovery is difficult and sometimes impossible.
Some parts of the body, such as the brain and eye, have long sensitive periods that extend throughout prenatal development. Other sensitive periods, such as those for the limbs and palate, are much shorter. In the period of the zygote, before implantation, teratogens rarely have any impact. If they do, the tiny mass of cells is usually so completely damaged that it dies. The embryonic period is the time when serious defects are most likely to occur because the foundations for all body parts are being laid down. During the fetal period, teratogenic damage is usually minor. However, organs such as the brain, ears, eyes, teeth, and genitals can still be strongly affected. The effects of teratogens go beyond immediate physical damage. Some health effects are subtle and delayed. As the Biology and Environment box above illustrates, they may not show up for decades. Furthermore, psychological consequencesmay occur indirectly, as a result of physical damage. For example, a defect resulting from drugs the mother took during pregnancy can affect others’ reactions to the child as well as the child’s ability to explore the environment. Over time, parent–child interaction, peer relations, and opportunities to explore may suffer. These experiences, in turn, can have far-reaching consequences for cognitive, emotional, and social development.
PRESCRIPTION AND NONPRESCRIPTION DRUGS
In the early 1960s, the world learned a tragic lesson about drugs and prenatal development.At that time, a sedative called thalidomide was widely available in Canada, Europe, and South America. When taken by mothers 4 to 6 weeks after conception, thalidomide produced gross deformities of the embryo’s developing arms and legs and, less frequently, damage to the ears, heart, kidneys, and genitals.About 7,000 infants worldwide were affected. As children exposed to thalidomide grew older, many scored below average in intelligence. Perhaps the drug damaged the central nervous system directly. Or the child-rearing conditions of these severely deformed youngsters may have impaired their intellectual development. Coffee, tea, cola, and cocoa contain another frequently consumed drug, caffeine.Heavy caffeine intake (more than three cups of coffee per day) is associated with low birth weight, miscarriage, and newborn withdrawal symptoms, such as irritability and vomiting.
■ The use of highly addictive mood-altering drugs, such as cocaine and heroin, has become more widespread, especially in poverty-stricken inner-city areas, where these drugs provide a temporary escape from a daily life of hopelessness. As many as 3 to 7 percent of American and Canadian babies born in large cities, and 1 to 2 percent of all North American newborns, have been exposed to cocaine prenatally. Babies born to users of cocaine, heroin, or methadone (a less addictive drug used to wean people away from heroin) are at risk for a wide variety of problems, including prematurity, low birth weight, physical defects, breathing difficulties, and death around the time of birth.
Throughout the first year, heroin- and methadone-exposed infants are less attentive to the environment than non exposed babies, and their motor development is slow. Evidence on cocaine suggests that some prenatally exposed babies develop lasting difficulties. Cocaine constricts the blood vessels, causing oxygen delivered to the developing organism to fall for 15 minutes following a high dose. It also can alter the production and functioning of neurons and the chemical balance in the fetus’s brain. These effects may contribute to an array of cocaine associated physical defects, including eye, bone, genital, urinary tract, kidney, and heart deformities; hemorrhages and seizures; and severe growth retardation. Another illegal drug, marijuana, is used more widely than heroin and cocaine. Studies examining its relationship to low birth weight and prematurity reveal mixed findings.
■ Although smoking has declined in Western nations, an estimated 12 percent of American women and 17 percent of Canadian women smoke during their pregnancies.The best-known effect of smoking during the prenatal period is low birth weight. But the likelihood of other serious consequences, such as miscarriage,
prematurity, impaired heart rate and breathing during sleep, infant death, and asthma and cancer later in childhood, is also increased. Nicotine, the addictive substance
in tobacco, constricts blood vessels, lessens blood flow to the uterus, and causes the placenta to grow abnormally. This reduces the transfer of nutrients, so the fetus gains weight poorly. Also, nicotine raises the concentration of carbon monoxide in the bloodstreams of both mother and fetus. Carbon monoxide displaces oxygen from red blood cells, damaging the central nervous system and slowing body growth in the fetuses of laboratory animals. Similar effects may occur in humans.
1. Fetal alcohol syndrome (FAS), distinguished by (a) slow physical growth, (b) a pattern of three facial abnormalities (short eyelid openings; a thin upper lip; a smooth or flattened philtrum, or indentation running from the bottom of the nose to the center of the upper lip), and (c) brain injury, evident in a small head and impairment in at least three areas of functioning—for example, memory, language and communication, attention span and activity level (over activity), planning and reasoning, motor coordination, or social skills. Other defects—of the eyes, ears, nose, throat, heart, genitals, urinary tract, or immune system—may also be present.Abel was diagnosed as having FAS.As is typical for this disorder, his mother drank heavily throughout pregnancy.
2. Partial fetal alcohol syndrome (p-FAS), characterized by (a) two of the three facial abnormalities just mentioned and (b) brain injury, again evident in at least three areas of impaired functioning. Mothers of children with p-FAS generally drank alcohol in smaller quantities, and children’s defects vary with the timing and length of
alcohol exposure. Furthermore, recent evidence suggests that paternal alcohol use around the time of conception may alter gene expression (see page 00 in Chapter 2),
thereby contributing to symptoms.
3. Alcohol-related neurodevelopmental disorder (ARND), in which at least three areas of mental functioning are impaired, despite typical physical growth and absence of facial abnormalities.Again, prenatal alcohol exposure, though confirmed, is less pervasive than in FAS. Even when provided with enriched diets, FAS babies fail to catch up in physical size during infancy or childhood. Mental impairment associated with all three FASD diagnoses is also permanent.
■ Ionizing radiation can cause mutation, damaging DNA in ova and sperm.When mothers are exposed to radiation during pregnancy, the embryo or fetus can suffer additional harm. Defects due to radiation were tragically apparent in the children born to pregnant. After each disaster, the incidence of miscarriage and babies born with underdeveloped brains, physical deformities, and slow physical growth rose dramatically. Even when a radiation-exposed baby seems normal, problems may appear later. For example, even low-level radiation, as the result of industrial leakage or medical X-rays, can increase the risk of childhood cancer. In middle childhood, prenatally exposed Chernobyl children had abnormal brain-wave activity, lower intelligence test scores, and rates of language and emotional disorders two to three times greater than those of non-exposed Russian children.
In industrialized nations, an astounding number of potentially dangerous chemicals are released into the environment. More than 75,000 are in common use in the United States, and many new pollutants are introduced each year. When 10 newborns were randomly selected from U.S. hospitals for analysis of umbilical cord blood,
researchers uncovered a startling array of industrial contaminants— 287 in all! They concluded that many babies are “born polluted” by chemicals that not only impair prenatal development but also increase the chances of life-threatening diseases and health problems later on. One established teratogen is mercury. High levels of prenatal mercury exposure disrupt production and migration of neurons, causing widespread brain damage. Pregnant women are wise to avoid eating long lived
predatory fish, such as swordfish, albacore tuna, and shark, which are heavily contaminated with mercury. For many years, polychlorinated biphenyls (PCBs) were used to insulate electrical equipment, until research showed that, like mercury, they found their way into waterways and entered the food supply. Women who frequently ate PCB-contaminated fish, compared with those who ate little or no fish, had infants with lower birth weights, smaller heads, persisting attention and memory difficulties, and lower intelligence test scores in childhood. Another teratogen, lead, is present in paint flaking off the walls of old buildings and in certain materials used in industrial occupations.High levels of prenatal lead exposure are consistently related to prematurity, low birth weight, brain damage, and a wide variety of physical
defects. Even low levels may be dangerous. In some studies, affected babies showed slightly poorer mental and motor development. In one investigation, unfavorable effects—in the form of increased delinquent and antisocial behaviors—were evident in adolescence.
■ Viruses. Five percent of women catch a virus of some sort while pregnant. Most of these illnesses, such as the common cold and various strains of the flu, have no impact on the embryo or fetus. A few, however, can result in extensive damage. The best known of these is rubella, otherwise known as three-day, or German,
measles. Infection during the fetal period is less likely to be harmful, but low birth weight, hearing loss, and bone defects may still occur. And the brain abnormalities resulting from prenatal rubella increase the risk of severe mental illness, especially schizophrenia, in adulthood.
The human immunodeficiency virus (HIV), which can lead to acquired immune deficiency syndrome (AIDS), a disease that destroys the immune system, has infected increasing numbers of women over the past two decades. Although the incidence of AIDS has declined in industrialized nations, the disease is rampant in developing countries. HIV-infected expectant mothers pass the deadly virus to the fetus 20 to 30 percent of the time. AIDS progresses rapidly in infants. By 6 months,weight loss, diarrhea, and repeated respiratory illnesses are common. The virus also causes brain damage, as indicated by seizures, gradual loss in brain weight, and delayed mental and motor development.
http://www.themedguru.com/node/840Other Maternal Factors
Besides avoiding teratogens, expectant parents can support the embryo and fetus in other ways. Regular exercise, good nutrition, and emotional well-being of the mother are essential. Problems that may result from maternal and fetal blood type differences can be prevented. Finally, many prospective parents wonder how a mother’s age affects the course of pregnancy.
We examine each of these factors in the following sections.
■ In healthy, physically fit women, regular moderate exercise, such as walking, swimming, biking, or an aerobic workout, is related to increased birth weight. However, very frequent, vigorous, extended exercise—working up a sweat for more than 30 minutes, four or five days a week especially late in pregnancy—results in lower birth
weight than in healthy controls. During the last trimester, when the abdomen grows very large, mothers have difficulty moving freely and often must cut back on exercise.Most women, however, do not engage in sufficient moderate exercise during pregnancy to promote their own and their baby’s health. Pregnant women with health problems, such as circulatory difficulties or a history of miscarriages, should consult their doctors about fitness routines. For these mothers, exercise
(especially the wrong kind) can endanger the pregnancy.
■ During the prenatal period,when children are growing more rapidly than at any other time, they depend totally on the mother for nutrients. A healthy diet, consisting
of a gradual increase in calories—an extra 100 calories a day in the first trimester, 265 in the second, and 430 in the third— resulting in a weight gain of 25 to 30 pounds (10 to 13.5 kilograms), helps ensure the health of mother and baby.
Consequences of Prenatal Malnutrition
Findings revealed that the sensitive-period concept operates with nutrition, just as it does with teratogens. The poorer the mother’s diet, the greater the loss in brain weight, especially if malnutrition occurred during the third trimester. During that time, the brain is increasing rapidly in size, and for it to reach its full potential, the mother must have a diet high in all the basic nutrients. An inadequate diet during pregnancy can also distort the structure of other organs, including the liver, kidney, and pancreas, resulting in lifelong health problems.
■ When women experience severe emotional stress during pregnancy, their babies are at risk for a wide variety of difficulties. Intense prenatal anxiety is associated with
a higher rate of miscarriage, prematurity, low birth weight, infant respiratory illness and digestive disturbances, and irritability during the first three years. It is also related to several commonly occurring physical defects, such as cleft lip and palate, heart deformities, and pyloric stenosis. When we experience fear and anxiety, stimulant hormones released into our bloodstream cause us to be “poised for action.” Large amounts of blood are sent to parts of the body involved in the defensive response—the brain, the heart, and muscles in the arms, legs, and trunk. Blood flow to other organs, including the uterus, is reduced. As a result, the fetus is deprived of a full supply of oxygen and nutrients. Stress hormones also cross the placenta, causing a dramatic rise in fetal heart rate and activity.They may permanently alter fetal neurological functioning as well, thereby heightening stress reactivity in later life.
■ When the inherited blood types of mother and fetus differ, serious problems sometimes result. The most common cause of these difficulties is Rh factor incompatibility. When the mother is Rh-negative (lacks the protein) and the father is Rhpositive (has the protein), the baby may inherit the father’s Rh-positive blood type. Rh-positive blood is dominant and Rh-negative blood is recessive, so the chances are good that a baby will be Rh-positive.) If even a little of a fetus’s Rh-positive blood crosses the placenta into the Rh-negative mother’s bloodstream, she begins to form antibodies to the foreign Rh protein. If these enter the fetus’s system, they destroy red blood cells, reducing the oxygen supply to organs and tissues.Mental retardation, miscarriage, heart damage, and infant death can occur. Because it takes time for the mother to produce Rh antibodies, firstborn children are rarely affected. The danger increases with each additional pregnancy. Fortunately, Rh incompatibility can be prevented in most cases.After the birth of each Rh-positive baby, Rh-negative mothers are routinely given a vaccine to prevent the buildup of antibodies. In emergency cases, blood transfusions can be performed immediately after delivery or, if necessary, even before birth.
MATERNAL AGE AND PREVIOUS BIRTHS
■ Research consistently indicates that healthy women in their thirties have about the same rates of prenatal and birth problems as those in their twenties. Complication rates increase, with a sharp rise among women age 50 to 55—an age at which, because of menopause (end of menstruation) and aging reproductive organs, few women can conceive naturally nature tries to ensure that once a girl can conceive, she is physically ready to carry and give birth to a baby. Infants born to teenagers have a higher rate of problems, but not directly because of maternal age. Most pregnant teenagers come from low income backgrounds, where stress, poor nutrition, and
health problems are common.
The Importance of Prenatal Health Care
Despite steady improvement over the past decade, unfortunately, 16 percent of pregnant women in the United States wait until after the first trimester to seek prenatal care, and nearly 4 percent receive none at all. Inadequate care is far more common among adolescent and low-income, ethnic minority mothers. Their infants are three
times as likely to be born underweight and five times as likely to die as are babies of mothers who receive early medical attention. Why do these mothers delay going
to the doctor? One reason is that they lack health insurance. Although the very poorest of these mothers are eligible for government-sponsored health services, many low-income women do not qualify. Besides financial hardship, some mothers have other reasons for not seeking early prenatal care.When researchers asked women who first went to the doctor late in pregnancy why they waited so long, they mentioned a wide variety of obstacles. These included both situational barriers—difficulty finding a doctor, getting an appointment, and arranging transportation, and insensitive or unsatisfying experiences with clinic staff—and personal barriers—psychological
stress, the demands of taking care of other young children, family crises, lack of knowledge about signs of pregnancy and benefits of prenatal care, and ambivalence about the pregnancy.Many were also engaging in high-risk behaviors, such as smoking and drug abuse, and did not want to reveal those behaviors to health professionals. Clearly, public education about the importance of early and sustained prenatal care for all pregnant women is badly needed. For women who are young, less educated, low-income, or under stress and therefore at risk for inadequate prenatal care, assistance in making appointments, drop-in child-care centers, and convenient, free or low-cost transportation—are vital. See also the Cultural Influences box on the following page, about the importance of culturally sensitive health-care practices. Finally, Applying What We Know below lists “do’s and don’ts” for a healthy pregnancy, based on our discussion of the prenatal environment.
Preparing for Parenthood
For most expectant parents, the prenatal period is not a time of medical hazard. Rather, it is a period of major life change accompanied by excitement, anticipation, and looking inward. The nine months before birth not only permit the fetus to grow but also give men and women time to develop a new sense of themselves as mothers and fathers. This period of psychological preparation is vital. How effectively individuals construct a parental identity during pregnancy has important consequences for the parent–child relationship. A great many factors contribute to the personal adjustments that take place.
We know most about how mothers adapt to the psychological challenges of pregnancy, although some evidence suggests that fathers use many of the same techniques. One common strategy is to seek information, as Yolanda and Jay did when they read books on pregnancy and childbirth and enrolled in my class. In fact, expectant mothers regard books as an extremely valuable source of information, rating them as second in importance only to their doctors. And the more a pregnant woman seeks information—by reading, accessing relevant websites, asking friends, consulting her own mother, or attending a prenatal class—the more confident she tends to feel about her own ability to be a good mother.
The Baby Becomes a Reality
At the beginning of pregnancy, the baby seems far in the future. Except for a missed period and some morning sickness (nausea that most women experience during the first trimester), the woman’s body has not changed much. But gradually, her abdomen enlarges, and the baby starts to become a reality. A major turning point occurs when expectant parents have concrete proof that a fetus is, indeed, developing inside the uterus. Parents get to know the fetus as an individual through these signs of life. And both may form an emotional attachment to the new being, dream about the future parent–infant relationship, and discuss names.
Models of Effective Parenthood
As pregnancy proceeds, expectant parents think about important models of parenthood in their own lives.When men and women have had good relationships with their own parents, they are more likely to develop positive images of themselves as parents during pregnancy. If their own parental relationships are mixed or negative, expectant mothers and fathers may have trouble building a healthy picture of themselves as parents. Some adults handle this challenge by seeking other examples of effective parenthood.
The Parental Relationship
The most important preparation for parenthood takes place in the context of the parents’ relationship. Expectant couples who are unhappy in their marriages and who have difficulty working out their differences continue to be distant, dissatisfied, and poor problem solvers after the baby is born. When a couple’s relationship is faring well and both partners want and planned for the baby, the excitement of a first pregnancy may bring husband and wife closer. At the same time, pregnancy does change
a marriage. Expectant parents must adjust their established roles to make room for children. In addition, each partner is likely to develop new expectations of the other.Women look for greater demonstrations of affection, interest in the pregnancy, and help with household chores. They see these behaviors as important signs of continued acceptance of themselves, the pregnancy, and the baby to come. Similarly, men are particularly sensitive to expressions of warmth from their partner. These reassure them of a central place in the new mother’s emotional life after the baby is born. When a relationship rests on a solid foundation of love and respect, parents are well equipped for the challenges of pregnancy. They are also prepared to handle the much more demanding changes that will take place as soon as the baby is born.