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A single sperm fertilizes an egg
as others continue
to try. |
The future of
babymaking
Scientists explore new
techniques for tackling
infertility
problems
By Jacqueline Stenson
Contributing editor
MSNBC
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Just
a few decades ago, it seemed pretty far-fetched to think
that postmenopausal
women could ever bear children
or that sterile men might fertilize eggs with sluggish
sperm. But researchers have overcome these and other medical
challenges
in the quarter-century since the birth of ‘test-tube’ baby
Louise Brown, a landmark event that brought the promise
of parenthood to millions of infertile couples. So what
will
the future of fertility hold? Transplanted wombs? Immortal
eggs?
Cloned babies?
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“The field has come a long way,” says Dr. Richard
Paulson, director of reproductive endocrinology and infertility
at the University of Southern California in Los Angeles.
Success
rates for in vitro fertilization procedures, in which egg and
sperm cells are combined in a lab dish, and other variations
of assisted reproductive technology are at an all-time high.
In 2000, the latest year for which U.S. statistics are available,
about 25 percent of treatment cycles involving a woman’s own
eggs resulted in a live birth.
Doctors attribute improved success
rates to such factors as better culture media — the fluid that
embryos are bathed in at the lab — and the ability to grow
many embryos for as long as five days before transfer to the
uterus, up from two or three days in the past.
Selecting better
embryos
To boost birth rates higher, scientists are working
to perfect current methods as well as develop new ones. One
area of research is the development of better techniques to
identify which embryos are the best candidates for transfer
to a woman’s uterus.
Some doctors currently use a screening
method called preimplantation genetic diagnosis, or PGD, which
involves removing a single cell from an embryo and testing
it for genetic defects.
The approach can be beneficial for
women who suffer repeat miscarriages due to chromosomal abnormalities,
but doctors say it has not proven its worth as a routine screening
technique for all patients.
Among its drawbacks,
PGD can damage embryos and may not always give accurate results
because one cell does not necessarily reflect the health
of the entire embryo, according to Paulson. An improvement,
he
says, would be a noninvasive test that would provide more
precise information, perhaps using a special microscope.
“The principle
of PGD — testing the embryo to see whether the DNA is right
or wrong — is clearly the way of the future,” says Paulson.
PGD is also being used increasingly with some fertile couples
to screen embryos for genetic conditions, such as cystic fibrosis
and Huntington’s disease. But, even if these diseases can be
identified, experts say they’re still a long way from being
able to “fix” embryos by altering their DNA.
Some researchers
also fear PGD will be used to create “designer babies” with
specific traits that have nothing to do with their health.
The technology is already being used in some cases solely to
choose a child’s sex.
“When does it stop being a medically
oriented procedure?” asks Dr. Randy Morris, an associate professor
of reproductive endocrinology at the University of Illinois
in Chicago.
“Do sex now, and eye color and free-throw-shooting
ability later? Whether society will tolerate that remains
to be seen,” says Morris.
Slowing the biological clock
Another
major goal of researchers is to figure out how to preserve
a woman’s fertility, which begins a nose dive in her mid-30s.
Scientists are trying to understand why eggs deteriorate and
how to thwart the process.
While doctors have long been attempting
to freeze eggs so that a young career woman, for instance,
could save them for use later in life, the process is not very
successful because the eggs are so fragile, says Dr. Michael
Soules, director of reproductive endocrinology and infertility
at the University of Washington in Seattle.
“It’s not good
enough to be attractive,” he says.
One approach that may
make egg freezing more successful is in vitro maturation,
in which
immature eggs are extracted from the ovaries and matured
in the lab. Immature eggs seem to survive freezing better
than
mature eggs, raising the possibility that doctors may one
day harvest and freeze the immature eggs and then thaw and
mature
them when a woman is ready to start a family.
The benefit
of in vitro maturation in routine ART is that it prevents
women
from having to undergo hormone injections to stimulate their
ovaries to release multiple mature eggs. The technique has
already been used to conceive some children but is still
being investigated. |
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| Later age pregnancy
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• Fertility
• Birth defects
• Detecting defects
• Difficult
pregnancy
• Mortality |
A third of women will not be able to conceive by
age 40. Medical researchers believe that the age of
eggs is a factor. Egg production is not a life-long
process. Rather, women are born with all of their eggs
and the more fertile eggs, according to studies, respond
to impregnation earlier in life.
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In
addition, older women have a greater likelihood
of contracting a reproductive-related complication
such as endometriosis, a malady where tissue attaches
itself to the ovaries or fallopian tubes, hampering
conception.Maternal age plays a factor in birth defects,
particularly those involving chromosomal complications
like Down syndrome. Birth defect risks associated
with mother's age.
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Age |
Down syndrome |
Other
abnormalities |
20 |
1 in 1,667 |
1 in 526 |
35 |
1 in 378 |
1 in 192 |
40 |
1 in 106 |
1 in 66 |
45 |
1 in 30 |
1 in 21 |
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Pregnant women 35 or older often choose prenatal
testing to detect any chromosomal abnormalities.
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Amniocentesis - Performed between week 14 and 18.
A needle is inserted through the abdominal wall and
into the amniotic sac surrounding the fetus. Fluid,
which contains fetus cells, is withdrawn and sent to
the lab, where the cells are tested for chromosomal
abnormality. |
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Chorionic
villus sampling - Performed between week
9 and 12. A small needle or tube is passed through
the cervix or the abdominal wall, extracting a small
piece of the placenta used for chromosomal studies. |
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Because diabetes and high blood pressure are more
common in women as they age, complications during pregnancy
are encountered with increased frequency in pregnant
women in their late 30s and 40s. Diabetic mothers are
at greater risk for preterm delivery and placental
problems. In addition, several bleeding complications
of pregnancy -- abruptio placentae and placenta previa
-- are also more frequent among older women.Recent
studies indicate that older pregnant women without
chronic medical disorders do not face an increase risk
of fatal complications. But because older women are
more susceptible to chronic medical disorders, numbers
on the whole point to an increased maternal mortality
rate. |
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Age |
Death (per 100,000 live births) |
30-34 |
15 |
35-39 |
22 |
over 40 |
60 |
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Source: National Center for Health Statistics,
Mayo Foundation, Associated Press, Center for Disease
Control
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Eggs
in abundance
Other high-tech tinkering may one day allow
for an abundant
supply
of new eggs or the rejuvenation
of old ones. Scientists, for instance, have coaxed embryonic
stem cells from mice to morph into eggs in the lab. If
the feat could be replicated in humans, it might offer
an alternative
for infertile couples who would otherwise need to rely
on donor eggs, which may be in short supply.
Other investigators
have
proposed a technique that involves taking the nucleus from
an infertile woman’s adult cell, such as a blood or skin cell,
and putting it into a hollowed-out egg from a donor. The goal
is to create an egg that has the genetic material of the infertile
woman and is healthy enough to be fertilized with her partner’s
sperm.
But experimentation with this technique and another
approach called cytoplasmic transfer, both of which involve
genetic manipulation beyond the direct union of egg and sperm,
were halted by the Food and Drug Administration in 2001, pending
agency approval.
During cytoplasmic transfer, cytoplasm — the part of the cell outside of the
nucleus — from a healthy donor egg is injected into an egg of an infertile woman
in an effort to make her egg healthier. Babies have already been created with
the technique and, because cytoplasm contains small amounts of genetic material,
the kids have been shown to have DNA from three genetic parents — two moms and
a dad — raising red flags with the FDA.
Transplanted or artifical wombs?
Science
may also have something new in store for women who are born without a uterus
or who must have it removed for health reasons — uterine transplants.
Doctors
in Saudi Arabia say they’ve transplanted a uterus into a woman but it had to
be removed after a few months because of blood-clotting problems. Other researchers
in Sweden have performed uterus transplants in mice, which were then able to
give birth.
Since the ideal donor would be a close genetic match, such as a mother
or sister, the ability to perform uterine transplants might actually make it
possible for a woman to give birth from the same uterus she was born from.
Uterine
transplants would offer an alternative to surrogacy but, on the downside, would
require patients to take anti-rejection drugs to prevent their immune systems
from attacking the organ.
Taking things even further, if embryos can be created
outside the womb, why can’t the fetus develop there, too, eliminating the need
for a uterus altogether?
Experts say the ability to fertilize and grow an embryo
outside the human body for a few days has been an amazing achievement, but one
that would pale in comparison to being able to nurture a fetus to term in the
lab.
“We’re just excited we can grow the embryo to day 5,” says Dr. Sherman Silber,
director of the Infertility Center of St. Louis at St. Luke’s Hospital. “Artificial
womb — I just don’t see that happening.”
Cloning conundrum
Meanwhile,
as researchers develop new fertility techniques, the debate over human cloning
continues to rage.
Amid all the ethical and moral concerns, fertility specialists
are skeptical human cloning would ever really be a practical — or desirable — option
for infertile couples.
But experts aren’t saying that it necessarily can’t be done.
“It’s possible,
if you go by all the different animals that have been cloned,” says Soules.
But
based on the animal experiments, scientists have learned that cloning efforts
fail the vast majority of the time and are plagued by high rates of birth defects
and other problems. In addition, no primates have ever been successfully cloned.
So what about those recent cloned-baby claims by Clonaid, a company linked to
the Raelian movement that believes space aliens created humans by cloning themselves?
“They’re
totally out in left field,” Silber says.
© 2004 MSNBC Interactive
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Infertility