Conceiving a baby through sexual
intercourse involves many steps. For conception to occur, a man’s sperm,
produced in his testes, must fertilize a woman’s egg, produced in her ovaries.
During sexual intercourse, sperm from the man are ejaculated (ejected during
orgasm) deep inside the woman’s vagina. The sperm travel into the uterus and up
the fallopian tubes (channels connecting the ovaries to the uterus), where the
sperm meet the egg. If a sperm is able to penetrate, or fertilize, an egg, and
if other conditions are favorable, the fertilized egg will travel from the
fallopian tube to the uterus, where it implants in the uterine lining. Fetal
development then begins.
CAUSES OF INFERTILITY
|
A problem or obstruction at any
point during conception prevents pregnancy from taking place. For about a third
of infertility cases, either physicians can find no cause, or the cause can be
traced to conditions in each partner that interact to cause infertility. About
a third of cases can be traced to causes specifically in the male, and about a
third to causes in the female.
Conditions Affecting Both Partners
|
A number of factors that
affect males and females alike can increase the risk of infertility. Perhaps
the most common problem is age—the older a person is, the more difficult it is
to become pregnant. Over the last 20 to 30 years there has been a trend to delay
childbearing, often until women are in their 30s. A woman reaches her peak
fertility at age 18 or 19, with little change until the mid-20s. As she
approaches age 30, her hormone levels start to decline and her fertility also
begins a slow decline, with a more rapid decline after age 35. Menopause, which
occurs in the late 40s to early 50s in most women, marks the end of a woman’s
natural ability to bear children. A man’s fertility decline is not as rapid and
has no clear-cut end point, but a man of 50 has lower hormone levels and is
likely less fertile than he was at age 25 or 30.
Genetics can also play a role in
infertility. An irregular genetic makeup in one or both partners can prevent
conception or result in a miscarriage, the spontaneous abortion of a fetus. Up
to 60 percent of miscarriages that occur in the first three months of pregnancy
result from genetic abnormalities.
Sexually transmitted infections (STIs)
are a leading cause of infertility. In many cases, diseases such as gonorrhea
and chlamydia may have no symptoms. If left untreated, STIs
can cause extensive and irreparable damage to reproductive organs. In women,
untreated STIs can cause pelvic inflammatory disease (PID), a bacterial
infection that damages the uterus, fallopian tubes, and ovaries. PID is one of
the primary causes of ectopic pregnancy, a life-threatening condition in which
the fetus begins to develop in the fallopian tube. In men, untreated STIs can
result in sterility, an inability to conceive.
In recent years fertility experts
have determined that in some cases the immune system may play a role in
preventing conception or interfering with embryo implantation in the uterus.
Both men and women can develop an allergic reaction to sperm, causing their
bodies to create antibodies that attack and kill sperm. These sperm antibodies
may also bring about infertility by causing sperm to clump together, preventing
them from fertilizing an egg.
Male Infertility Factors
|
Historically men were assumed to be
fertile if they were capable of sexual intercourse. As a partial consequence of
this attitude, research on fertility has traditionally emphasized problems in
women. More recently, however, physicians have found that the male partner is
the primary cause of infertility in about 30 percent of cases. Causes of male
infertility can be categorized into sperm abnormalities, structural problems,
or medical disorders.
Sperm Abnormalities
|
Low sperm count is the most
frequent cause of male infertility. Although ultimately only one sperm is
required for fertilization, men whose semen (fluid produced during ejaculation)
contains less than 20 million sperm per milliliter frequently have infertility
problems.
In addition to the quantity
of sperm, the quality of sperm may affect male fertility. Physicians determine
sperm quality according to its motility (ability to move) and its physical
structure. Poor motility will prevent sperm from swimming the long distance
from the woman’s vagina to the fallopian tubes to fertilize an egg. Sperm that
have structural problems will also have problems penetrating an egg. Other
conditions that can compromise sperm quality include genetic impairments such
as damaged deoxyribonucleic acid (DNA), the genetic information critical in the
development of a fertilized egg; or degradation that may result if sperm is
stored too long after its formation.
Structural Abnormalities
|
Some men have anatomical
abnormalities that impair or prevent fertility. The most common structural
problem affecting male sperm levels is a varicocele, a tangle of
swollen veins surrounding the testis. Other testicular problems include
torsion, in which one testis is twisted, or undescended testicles, in which the
testes are located in the abdomen instead of in the scrotum, the external pouch
of skin that normally holds the testes. The vas deferens (tubes that carry
sperm from the testes to the penis) may be blocked because of a past infection
or injury, or may be absent altogether due to a congenital abnormality. Other
structural problems may prevent a man from ejaculating or cause his ejaculation
to propel the sperm backward into his bladder rather than out through the
penis.
Medical Disorders
|
A number of medical disorders
may cause male infertility. Infections such as sexually transmitted infections,
prostatitis (infection of the prostate gland), and mumps contracted as an adult
may lead to scarring and obstruction of the reproductive organs. Certain
medications, including some prescribed to control high blood pressure (calcium
channel blockers and beta blockers), ulcers (cimetidine), and depression (MAO
inhibitors), can impair testicular function. Exposure to high levels of
environmental toxins, including lead, mercury, and certain pesticides, may also
affect male fertility. Some men have insufficient hormone levels, resulting in
low sperm count or improper testicular function.
Female Infertility Factors
|
Assisted Reproductive Technologies
In these methods used to treat infertility, three methods (IVF,
ZIFT, and ICSI) artificially induce the union of sperm and egg in the
laboratory before implanting the fertilized egg inside the female reproductive
system. The fourth method (GIFT) mixes unfertilized eggs and sperm in the
laboratory before transferring them to the fallopian tube, where fertilization
takes place naturally.
Many factors can affect a woman’s
ability to ovulate (monthly release of an egg from the ovaries), conceive, or
carry a pregnancy to term. Female infertility factors are commonly grouped in
two categories: structural abnormalities and hormonal imbalances.
Structural Abnormalities
|
Some women are born with
reproductive systems that have anatomical irregularities, or infection or
injuries may damage certain reproductive organs. Blocked fallopian tubes are a
frequent cause of female infertility, accounting for up to 35 percent of cases
among females. Scar tissue that blocks the fallopian tubes—caused by infection,
inflammation, or a condition called endometriosis—prevents eggs from meeting
sperm.
Sometimes a woman is born
with a malformed cervical canal. An impaired cervical canal can prevent passage
of sperm from the vagina to the uterus as the sperm travel toward the fallopian
tubes. If a woman is able to conceive, problems with the cervical canal can
lead to miscarriage. In the uterus, noncancerous growths, such as fibroid
tumors and polyps, can prevent a fertilized egg from implanting in the uterine
wall.
Hormonal Imbalance
|
A frequent cause of infertility
in women is abnormal ovulation. Normally one egg will be released each month
about midway through the menstrual cycle, under the direction of several
hormones. If any of these hormones are not functioning, ovulation will occur
irregularly or perhaps not at all. This condition accounts for about 25 percent
of cases of female infertility.
Abnormal ovulation can be caused by a
number of disorders of the endocrine system, including thyroid disease,
diabetes mellitus, and polycystic ovarian syndrome. Certain chemicals can
affect hormonal levels and adversely affect fertility. For instance, marijuana
use can shorten the menstrual cycle. Cigarette smoking reduces some types of
hormone production and may deplete egg supply.
Other Factors
|
A number of other factors
also may contribute to female infertility. Once inside the female’s cervix,
sperm may encounter obstacles. The cervical mucus (thick fluid that protects
the cervix and uterus from infection) may be too thick for the sperm to penetrate,
or it may be chemically hostile to the sperm. A fertilized egg may become stuck
in the fallopian tube and result in an ectopic pregnancy.
DIAGNOSING THE CAUSE
|
With so many factors affecting
infertility, finding the exact cause or causes can often be a challenge. To
avoid unnecessary testing and treatment, most doctors will not make the
diagnosis of infertility until one year of unprotected intercourse has failed
to result in pregnancy. This is because even among fertile couples the chance
of conception in any given month is only about 20 percent. In cases involving
older couples or where there is evidence of infertility with previous partners,
physicians may diagnose infertility sooner so they can try to identify the
cause and begin aggressive treatment. Once physicians diagnose infertility,
they use medical histories, physical examinations, and laboratory tests to find
its cause.
A doctor will begin an
evaluation by asking both partners about their medical histories to identify
past illnesses, injuries, surgeries, or prescription drug use that may affect
fertility. The medical history should also uncover information about past
pregnancies or miscarriages, risky behaviors (such as smoking, frequent hot tub
use, or the use of harmful drugs), and exposure to hazardous chemicals from
jobs or hobbies. In addition, the doctor may ask about medical problems of
other family members to determine if an inherited disorder exists within a
family.
Following the medical history, a
doctor will give both partners a physical examination of the reproductive
system. In men, the doctor will examine the testes, penis, scrotum, and
prostate for structural defects or infections. The doctor will also search for
obvious signs of hormonal imbalance, including enlarged breasts or excessive
body or facial hair. In women, the doctor will look for structural problems or
disease in the vagina, cervix, uterus, and fallopian tubes. Outward signs of hormonal
imbalance in women may include the presence of excessive hair, acne, or
obesity.
Doctors use laboratory tests to
uncover factors that cause infertility. In men, a semen analysis determines the
quantity and health of sperm. In women, the primary focus of laboratory tests
is to determine if a woman ovulates properly. Since hormones regulate
ovulation, a doctor may order a number of blood tests performed over a period
of a month to identify levels of sex hormones—estrogen, follicle-stimulating
hormone (FSH), and luteinizing hormone (LH)—during different stages of the
menstrual cycle. Testing in women may also include an X ray of the fallopian
tubes to determine whether the tubes are blocked.
TREATMENT
|
Once the cause or causes of
infertility are determined, doctors devise a strategy for the couple to
increase their fertility. Structural problems, such as varicoceles or blocked
ejaculatory ducts in men and fallopian tube obstruction in women, can be treated
by surgery. When no structural problems are identified, infertility treatments
usually begin with noninvasive measures. Sometimes only small adjustments in
the frequency and timing of sexual intercourse are required to bring about
pregnancy. Couples are instructed in how to identify when a woman is ovulating
so that they can plan sexual intercourse around her most fertile time.
Practices that temporarily result in lowered sperm counts or damaged sperm can
be curtailed, such as the use of certain medications, alcohol, marijuana, and
hot tubs or saunas. If these noninvasive measures are unsuccessful, a doctor
may recommend fertility drugs or assisted reproductive technologies.
Fertility Drugs
|
Experts estimate that more than 75
percent of infertility cases due to hormonal problems can be treated with
fertility drugs. One or more fertility drugs, such as clomiphene, human
menopausal gonadotropin (HMG), and an injectable form of follicle-stimulating
hormone, may be prescribed to women to treat ovulatory disorders, such as
failure to ovulate or infrequent or erratic ovulation. Fertility drugs may also
be used to treat male infertility. For example, men may use HMG to stimulate
sperm production.
Although fertility drugs are commonly
used in treating infertility, they can produce health problems in some women,
such as ovarian hyperstimulation syndrome, a potentially dangerous disorder in
which the ovaries enlarge and fluid accumulates in the abdomen. In addition,
fertility drugs can cause more than one egg to release during ovulation,
increasing the risk of multiple pregnancies. Studies show that a combination of
dietary counseling, exercise, and the drug metformin (commonly used to treat
diabetes mellitus) is equally effective as fertility drugs in regulating
ovulation, with less risk to health and fewer multiple births.
Assisted Reproductive Technologies
|
In addition to the conventional
methods of fertility treatment, a number of techniques, collectively known as
assisted reproductive technologies (ART), can assist couples in becoming
pregnant. The best known of these is in vitro fertilization (IVF). In IVF, a
woman receives fertility drugs in order to produce multiple eggs. These eggs
are removed from the female during an outpatient procedure, then taken to a
laboratory and mixed with specially treated semen in a petri dish. If a sperm
fertilizes an egg to form an embryo, a physician transfers the embryo to the
woman's uterus, where it implants and develops during a normal pregnancy. In
many cases, physicians will transfer more than one embryo to increase the
chance that a pregnancy will occur. Often, multiple pregnancies result.
A variation of IVF is gamete
intrafallopian transfer (GIFT), in which an egg and sperm are placed in the
woman's fallopian tube, permitting fertilization to occur naturally. In zygote
intrafallopian transfer (ZIFT), eggs and sperm are mixed in a laboratory dish
using the same process as IVF. A physician transfers a resulting embryo into
the fallopian tubes. The embryo then follows the natural process and travels to
the uterus for implantation. Both GIFT and ZIFT are more expensive than IVF and
result in similar pregnancy rates as IVF, so these two methods are now rarely
used. Intracytoplasmic sperm injection (ICSI) is routinely performed in cases
where the man has extremely low sperm counts. In this procedure a single sperm
is extracted from a sperm sample and injected into an egg. The resulting embryo
is then inserted into the uterus using IVF procedures.
Although ART procedures have been
dramatically refined and improved in recent years, success rates range only
from 11 to 37 percent, depending on the technique used, the age of the woman
treated, and the severity of the couple’s infertility problems. In cases where
ART is successful, about one-third of cases result in multiple pregnancies. To
improve the odds of success, and also to reduce the risk of multiple
pregnancies, researchers are developing more effective ways to evaluate embryos
created using ART. This will enable doctors to identify and transfer the one
embryo that has the best chance of implanting and developing in the uterus.
Another method that may improve
the success rate of producing a healthy baby through ART is preimplantation
genetic diagnosis (PGD). When genetic testing indicates that a couple is at
increased risk for passing a specific genetic abnormality to a child, PGD
enables doctors to take a single cell from a newly developing embryo and
analyze its genetic makeup. This procedure may reduce the risk of miscarriage
from an embryo with genetic abnormalities and lessen the chance that a child
will be born with a genetic disorder.
ETHICAL ISSUES
|
The rapid development of ART has
raised many ethical and legal issues. Philosophers, theologians, and medical
ethicists question the right of humans to tamper with natural processes.
Some observers fear that the
availability of ART will give humans the ability to manipulate their genetic
heredity. Opponents of reproductive technologies take issue with techniques
that enable doctors to identify and select sperm, eggs, or embryos before they
are implanted. They argue that these techniques will someday permit parents to
select certain idealized standards, such as the absence of minor defects, or
choose a preferred gender for their baby. Many critics fear that these
technologies may one day help parents create a genetic photocopy of themselves.
Some of the ethical questions
surrounding abortion also arise in the field of fertility technology. Fertility
treatment may result in multiple pregnancies, which can endanger the health of
the mother and babies. When multiple pregnancies occur, doctors can selectively
abort one or more of the embryos to improve the survival chances of the others
and to reduce the burden on parents of raising quintuplets or sextuplets.
Furthermore, in a world where
millions of existing children are orphans and poverty stricken, many people
question spending thousands of scarce medical-care dollars to enable affluent
couples to have babies of their own biological parentage. Health-care
policymakers debate whether infertility treatment is a basic right that should
be paid for by medical insurance, or an elective luxury, similar to cosmetic
surgery, available only to those who can pay the price.
In addition to these ethical issues, fertility
practitioners and their patients have more immediate concerns, such as deciding
the fate of unused eggs, sperm, and embryos. If these reproductive cells are
frozen and stored, decisions must be made about how long they will be kept and
at whose expense. Further issues involve custody of embryos if the parents
divorce or die. Infertility treatments may involve considerable time, expense,
and loss of privacy. As a result, many couples find that dealing with
infertility and its treatment is stressful and puts a strain on relationships.
Physicians often recommend that couples undergo private counseling or
participate in infertility support groups to help deal with infertility-related
issues.
