Reproduction revolution: Sex for fun, IVF for children
Reproduction revolution: Sex for fun, IVF for children
Original here
20 October 2006
Jo Whelan
In the science fiction movie Gattaca, the hero, Vincent, is an "In-Valid" - someone whose only crime is to be conceived in a moment of passion rather than in a Petri dish. His brother, by contrast, is a Valid, created by a process designed to ensure the optimum recombination of his parents' genes. In-Valids are condemned to a life of menial jobs and discrimination. To realise his dream of becoming an astronaut, Vincent has to buy a Valid's identity.
It's a scenario that is difficult to imagine from today's viewpoint. Yet could we be moving towards an age in which entering nature's genetic lottery is no longer seen as a desirable way to bring a child into the world? Might natural conception even come to be thought of as irresponsible, as bad as smoking while pregnant?
Reproducing the traditional way is undoubtedly flawed. Worldwide around 1 child in 16 is born with a mental or physical disability due to a genetic defect, and most of us probably carry gene variants that predispose us to serious illnesses later in life. How much safer it would be to go along to the fertility clinic, have some embryos created and pick the one or two that will produce the healthiest baby.
IVF has become commonplace, and top clinics boast pregnancy rates of more than 30 per cent for each cycle - better than the 1 in 4 chance of conceiving the natural way and likely to improve further. Until recently, though, IVF was only for those with fertility problems. The rapid development of pre-implantation genetic diagnosis is starting to change this. Increasing numbers of fertile couples with a family history of a serious disease such as cystic fibrosis are opting for IVF with PGD so they can be sure any child will not inherit it. Others are resorting to IVF-PGD so they can choose their child's most basic characteristic: sex. Women who freeze their eggs to ensure they can have children later in life (see Methuselah moms) may soon swell the ranks even further. Could IVF-PGD one day become the preferred method of conception?
"It is technically possible," says Simon Fishel, a member of the team responsible for the birth of the first IVF baby in 1978, who now runs the Care Fertility group of clinics in the UK. There are, of course, huge obstacles, not least of which is the cost. "You have to pay per cycle," points out Fishel. "You can attempt to conceive naturally over 12 cycles in a year and it costs you nothing."
If the benefits were clear, though, many couples might save up to give their children the best start in life, just as many now pay for private schooling. In some countries, state healthcare systems or medical insurers might foot the bill, at least for those who risk passing on severe diseases. New Zealand is leading the way, providing limited funding of IVF-PGD for couples whose children risk inheriting serious diseases. It remains to be seen how many countries will follow suit, but there is a strong ethical argument for offering prospective parents this option and, given the huge costs of treating many genetic illnesses, a strong financial case too.
The other big obstacles are the inconvenience, pain and risk involved. Women have to inject themselves for weeks with expensive hormones that stimulate their ovaries to produce more eggs than normal and then have the eggs extracted, with only a 1 in 3 chance of getting pregnant. It's an emotional roller-coaster ride.
In up to 10 per cent of IVF cycles the extra hormones trigger ovarian hyperstimulation syndrome, in which fluid leaks from blood vessels, causing symptoms such as bloating and pain. Around 5 per cent of cycles cause moderate or severe OHSS, with a risk of disabling strokes or even death. For every 100,000 women undergoing IVF, about six die.
While the hunt is on for ways to prevent hyperstimulation, it would be best to avoid ovary-stimulating drugs altogether, not least because there are fears that they might slightly increase the risk of some cancers. One alternative is in vitro oocyte maturation, or IVM. Early in the cycle the ovaries contain many eggs that are nearly mature, but only one completes development each month; the others degenerate. Instead of relying on drugs to force all these eggs to reach the ovulation stage, IVM involves harvesting nearly mature eggs and incubating them for one or two days to complete their development.
Several hundred children have already been born after IVM, and follow-up of the children has so far not revealed any ill effects. As well as being less risky for women, IVM is cheaper. "It is impossible to say if IVM will replace conventional IVF; its efficiency, efficacy and safety are still far from certain. But it could happen," says Fishel.
What about the health of the children? The greatest threat is the practice of implanting several embryos to boost the chances of a pregnancy, resulting in more twins and triplets, who face far greater health risks than singletons. They are more likely to be born prematurely or have a low birthweight, with all the lifelong problems these can entail, and to die soon after birth.
Even singleton IVF babies are around twice as likely to be premature or low birthweight. Again, however, multiple embryos could be to blame, because many IVF pregnancies start out as twin pregnancies. When single embryos are transferred, the differences in health vanish (New Scientist, 25 June 2005, p 14). Many countries limit the number of embryos that can be implanted and single embryo transfer could eventually become the norm.
An IVF baby is also three times as likely to be born with Beckwith-Wiedemann syndrome, which can lead to growth abnormalities and cancers. There are just 4 cases per 15,000 births even after IVF, however, and the higher risk might be due to parents' fertility problems rather than to IVF.
Despite these issues, by the time IVF children are 8 years of age they are indistinguishable from those conceived naturally. Other problems may emerge in old age, but it will be decades before we find out. There is a similar situation with PGD, which usually involves removing one or two cells from an eight-cell embryo for testing. Studies of children born after PGD have found no ill effects, but many experts question whether we can yet be certain the procedure is safe.
For the 1 in 6 couples with fertility problems, or those who know their children risk inheriting a serious genetic disease, IVF and PGD are already well worth the cost and risk. For the rest of us, of course, they are not. However, this balance looks certain to change as IVF becomes safer and more affordable and as PGD offers ever more possibilities.
Imagine if you could be almost certain that your child would be free of any known genetic disease. Not only that, you could choose your baby's sex and perhaps even select aspects of their appearance or intellectual and physical capabilities. Given these options, millions more people may be prepared to go down the assisted reproduction route.
"Any genetic defect that has been identified can now be screened for," says Alan Handyside of London's Bridge Fertility Centre, who led the team that pioneered PGD in 1989. As the genetic basis of ever more disorders is pinpointed, and more and more families discover that they harbour harmful mutations, the attraction of PGD will grow.
For the moment, though, with the exception of major chromosomal disorders, PGD can only detect mutations already identified in the would-be parents. It cannot detect unexpected mutations that arise spontaneously in the sperm or eggs of individuals who do not carry the mutation themselves. This will become possible, however, as our knowledge grows.
Part of the problem is that only one or two cells are available for screening. Until recently this greatly restricted the tests that could be done. However, new ways of amplifying DNA are making it possible to do hundreds of tests. That means clinics will be able to screen for a much wider range of harmful mutations - and for desirable variants too.
It is already easy to determine sex, and thousands of fertile couples are now choosing to have IVF-PGD for sex selection, as it is more reliable than competing methods such as sperm sorting. A recent survey found that 9 per cent of PGD in the US is for sex selection (New Scientist, 30 September, p 15), and the phenomenon is not restricted to western countries: in sub-Saharan Africa, for instance, more and more fertility clinics are offering this service, says fertility expert Osato Giwa-Osagie of Lagos Teaching Hospital in Nigeria.
Needless to say, the issue is contentious. One of the main objections to sex selection is that it could skew the balance of the sexes. In many parts of Asia and Africa, male children are sought after. However, in western countries, the opposite seems to be true. "The vast majority of patients who come to us request girls," says Trina Leonard of the Genetics and IVF Institute in Fairfax, Virginia, which offers a sperm-sorting technique and PGD.
Many countries, including the UK and Australia, do not allow sex selection for non-medical reasons. Where it is allowed, some clinics restrict sex selection to family balancing, meaning a couple must already have a boy if they request a girl and vice versa. "You can't come here and say 'I want a family of five boys'," says Leonard. But half of the clinics in the US that carry out PGD for sex selection do not insist on family balancing, and many of their clients are couples from countries where sex selection is banned.
In the long term, it may be hard for regulatory authorities to continue to deny access to sex selection. "The reality is that the technology is available, and people want access to it," says Fishel. John Harris, a bioethicist at the University of Manchester, UK, sees no moral or ethical objection to sex selection. He suggests that a trial number of procedures should be allowed to see if fears about the social impact are justified.
How much further can selection go? What of that object of tabloid hysteria, the "designer baby"? Will we one day be able to ask for a tall, musical, blue-eyed boy or a dark-haired girl? Even if regulatory authorities allow us to use PGD to select desirable gene variants, there are major snags. For starters, IVF typically generates fewer than 10 embryos per cycle. This means parental choice will be very limited. "I don't think anyone in their right mind would ever go through IVF to select the hair colour of their offspring," says Yuri Verlinsky of the Reproductive Genetics Institute, Chicago, one of the pioneers of PGD.
"The only way to increase choice would be to generate larger numbers of eggs," says Handyside. It might become possible to do this by maturing early-stage eggs taken from the ovaries in the lab, or by generating eggs from stem cells (see The egg and sperm race). Even then, the options will still be limited. "Unless we interfere with the genes of an embryo, children are going to resemble their parents," says Handyside. "The genes for particular characteristics may not be there."
What's more, predicting which of 100 embryos will turn into the most intelligent child or the greatest athlete will require enormous advances. "If tomorrow there was a publication saying that we have managed to identify all the genes involved in intelligence, then screening for it would be available in a few years," says Fishel. "But until there is a breakthrough in our knowledge it looks improbable that we could screen for amorphous traits like that, because we do not really know what they involve."
And the choices will not always be easy. Would you opt for gene variants that boost creativity if they also increased the risk of mental health problems, for instance? For would-be parents, simply understanding the information available will be difficult and the weight of decision-making will be far heavier. Even the decision not to screen will be a fraught one. It would be sad if this burden came to overshadow the thrill and wonder of bringing a new life into the world.
On the other hand, if screening for IQ does become possible there could be huge demand for it. Like it or not, we will be faced with new reproductive options - if societies choose to allow them. "We are going to have the technical ability to look at a very fine scale at the genetics of embryos in vitro and in pregnancy," says Handyside. "There are huge challenges for society to adapt and to work out where we should draw the line, what we should be looking for and what we should do with this information."
The battle over how this technology is used will shape the way future generations reproduce. The ethics of embryo selection will be pitted against the ethics of denying it to people who want it. Yet according to Harris, this is a false dilemma. "No embryo has a right to be implanted, and a woman has no obligation to have any embryo implanted if she does not want to," he says. "She makes a choice about which embryo, if any, to accept. I cannot see any justification for her being denied the information to make that choice rationally."
"There should be no restriction on using PGD for diagnosing disease," says Verlinsky. "Everyone wants to protect their children; nobody wants to see them go through the same horror that someone else in their family did."
If people continue leaving childbirth ever later in life, there is no doubt that increasing numbers will have to resort to IVF. The growing advantages of PGD may persuade more and more fertile couples to join them. So will old-fashioned sex ever fall out of favour as a way of making babies? It is certainly not going to happen in the next 10 or 20 years, but in the next 50 or 100 - who knows? After all, who would have predicted how common IVF would become back in 1977, when Louise Brown was just a speck in a Petri dish?
Jargon buster
IVF
Used here to refer to any form of fertilisation outside the body. Doctors, however, distinguish between conventional IVF - placing sperm with an egg in a dish and leaving them to it - and ICSI (intracytoplasmic sperm injection), where a single sperm is injected into an egg.
PGD
Pre-implantation genetic diagnosis. The testing of IVF embryos before implantation by removing one or more cells for analysis. Also refers to the testing of eggs before fertilisation. Not to be confused with prenatal testing during pregnancy.
IVM
In vitro maturation. A new method that involves collecting immature eggs and maturing them outside the body, instead of using drugs to stimulate women to produce many mature eggs. Its safety is not yet clear.
In vitro figures
30,000 IVF children were born worldwide in 1989 and at least 200,000 in 2002
Well over 3 million children worldwide have been conceived by IVF since 1978
In Denmark and the Netherlands 1 in 25 babies are conceived in a dish
A window on the womb
You don't have to resort to IVF-PGD to screen for genetic disorders. Tests can also be carried out during pregnancy. Obtaining fetal cells involves invasive procedures that can trigger miscarriages, however, so such tests are usually done only if scans reveal an abnormality or if there's a high chance of a child inheriting a serious disease. Prenatal screening is also routine to confirm the results of PGD, which will never be 100 per cent reliable.
Most tests look for major chromosomal disorders, such as Down's syndrome. In Europe more than 90 per cent of fetuses with Down's are aborted, so fewer and fewer children are born with the disorder, despite the rising number of older mothers (see "The egg and sperm race").
More wide-ranging prenatal genetic tests are becoming available. Art Beaudet's team at Baylor College of Medicine in Houston, Texas, now offers screening for more than 150 different genetic abnormalities, using a technique called array-CGH to look for parts of chromosomes that have been duplicated or deleted.
Safer, non-invasive methods, such as isolating fetal DNA or cells from a mother's blood, could lead to prenatal genetic screening becoming more common. However, some geneticists say we do not yet know enough to routinely apply tests such as Beaudet's: the amount of information such tests can yield is growing faster than our ability to interpret it. And an abnormal result will always confront parents with the agonising decision of whether or not to terminate the pregnancy.
From issue 2574 of New Scientist magazine, 20 October 2006, page 42-45
Original here
20 October 2006
Jo Whelan
In the science fiction movie Gattaca, the hero, Vincent, is an "In-Valid" - someone whose only crime is to be conceived in a moment of passion rather than in a Petri dish. His brother, by contrast, is a Valid, created by a process designed to ensure the optimum recombination of his parents' genes. In-Valids are condemned to a life of menial jobs and discrimination. To realise his dream of becoming an astronaut, Vincent has to buy a Valid's identity.
It's a scenario that is difficult to imagine from today's viewpoint. Yet could we be moving towards an age in which entering nature's genetic lottery is no longer seen as a desirable way to bring a child into the world? Might natural conception even come to be thought of as irresponsible, as bad as smoking while pregnant?
Reproducing the traditional way is undoubtedly flawed. Worldwide around 1 child in 16 is born with a mental or physical disability due to a genetic defect, and most of us probably carry gene variants that predispose us to serious illnesses later in life. How much safer it would be to go along to the fertility clinic, have some embryos created and pick the one or two that will produce the healthiest baby.
IVF has become commonplace, and top clinics boast pregnancy rates of more than 30 per cent for each cycle - better than the 1 in 4 chance of conceiving the natural way and likely to improve further. Until recently, though, IVF was only for those with fertility problems. The rapid development of pre-implantation genetic diagnosis is starting to change this. Increasing numbers of fertile couples with a family history of a serious disease such as cystic fibrosis are opting for IVF with PGD so they can be sure any child will not inherit it. Others are resorting to IVF-PGD so they can choose their child's most basic characteristic: sex. Women who freeze their eggs to ensure they can have children later in life (see Methuselah moms) may soon swell the ranks even further. Could IVF-PGD one day become the preferred method of conception?
"It is technically possible," says Simon Fishel, a member of the team responsible for the birth of the first IVF baby in 1978, who now runs the Care Fertility group of clinics in the UK. There are, of course, huge obstacles, not least of which is the cost. "You have to pay per cycle," points out Fishel. "You can attempt to conceive naturally over 12 cycles in a year and it costs you nothing."
If the benefits were clear, though, many couples might save up to give their children the best start in life, just as many now pay for private schooling. In some countries, state healthcare systems or medical insurers might foot the bill, at least for those who risk passing on severe diseases. New Zealand is leading the way, providing limited funding of IVF-PGD for couples whose children risk inheriting serious diseases. It remains to be seen how many countries will follow suit, but there is a strong ethical argument for offering prospective parents this option and, given the huge costs of treating many genetic illnesses, a strong financial case too.
The other big obstacles are the inconvenience, pain and risk involved. Women have to inject themselves for weeks with expensive hormones that stimulate their ovaries to produce more eggs than normal and then have the eggs extracted, with only a 1 in 3 chance of getting pregnant. It's an emotional roller-coaster ride.
In up to 10 per cent of IVF cycles the extra hormones trigger ovarian hyperstimulation syndrome, in which fluid leaks from blood vessels, causing symptoms such as bloating and pain. Around 5 per cent of cycles cause moderate or severe OHSS, with a risk of disabling strokes or even death. For every 100,000 women undergoing IVF, about six die.
While the hunt is on for ways to prevent hyperstimulation, it would be best to avoid ovary-stimulating drugs altogether, not least because there are fears that they might slightly increase the risk of some cancers. One alternative is in vitro oocyte maturation, or IVM. Early in the cycle the ovaries contain many eggs that are nearly mature, but only one completes development each month; the others degenerate. Instead of relying on drugs to force all these eggs to reach the ovulation stage, IVM involves harvesting nearly mature eggs and incubating them for one or two days to complete their development.
Several hundred children have already been born after IVM, and follow-up of the children has so far not revealed any ill effects. As well as being less risky for women, IVM is cheaper. "It is impossible to say if IVM will replace conventional IVF; its efficiency, efficacy and safety are still far from certain. But it could happen," says Fishel.
What about the health of the children? The greatest threat is the practice of implanting several embryos to boost the chances of a pregnancy, resulting in more twins and triplets, who face far greater health risks than singletons. They are more likely to be born prematurely or have a low birthweight, with all the lifelong problems these can entail, and to die soon after birth.
Even singleton IVF babies are around twice as likely to be premature or low birthweight. Again, however, multiple embryos could be to blame, because many IVF pregnancies start out as twin pregnancies. When single embryos are transferred, the differences in health vanish (New Scientist, 25 June 2005, p 14). Many countries limit the number of embryos that can be implanted and single embryo transfer could eventually become the norm.
An IVF baby is also three times as likely to be born with Beckwith-Wiedemann syndrome, which can lead to growth abnormalities and cancers. There are just 4 cases per 15,000 births even after IVF, however, and the higher risk might be due to parents' fertility problems rather than to IVF.
Despite these issues, by the time IVF children are 8 years of age they are indistinguishable from those conceived naturally. Other problems may emerge in old age, but it will be decades before we find out. There is a similar situation with PGD, which usually involves removing one or two cells from an eight-cell embryo for testing. Studies of children born after PGD have found no ill effects, but many experts question whether we can yet be certain the procedure is safe.
For the 1 in 6 couples with fertility problems, or those who know their children risk inheriting a serious genetic disease, IVF and PGD are already well worth the cost and risk. For the rest of us, of course, they are not. However, this balance looks certain to change as IVF becomes safer and more affordable and as PGD offers ever more possibilities.
Imagine if you could be almost certain that your child would be free of any known genetic disease. Not only that, you could choose your baby's sex and perhaps even select aspects of their appearance or intellectual and physical capabilities. Given these options, millions more people may be prepared to go down the assisted reproduction route.
"Any genetic defect that has been identified can now be screened for," says Alan Handyside of London's Bridge Fertility Centre, who led the team that pioneered PGD in 1989. As the genetic basis of ever more disorders is pinpointed, and more and more families discover that they harbour harmful mutations, the attraction of PGD will grow.
For the moment, though, with the exception of major chromosomal disorders, PGD can only detect mutations already identified in the would-be parents. It cannot detect unexpected mutations that arise spontaneously in the sperm or eggs of individuals who do not carry the mutation themselves. This will become possible, however, as our knowledge grows.
Part of the problem is that only one or two cells are available for screening. Until recently this greatly restricted the tests that could be done. However, new ways of amplifying DNA are making it possible to do hundreds of tests. That means clinics will be able to screen for a much wider range of harmful mutations - and for desirable variants too.
It is already easy to determine sex, and thousands of fertile couples are now choosing to have IVF-PGD for sex selection, as it is more reliable than competing methods such as sperm sorting. A recent survey found that 9 per cent of PGD in the US is for sex selection (New Scientist, 30 September, p 15), and the phenomenon is not restricted to western countries: in sub-Saharan Africa, for instance, more and more fertility clinics are offering this service, says fertility expert Osato Giwa-Osagie of Lagos Teaching Hospital in Nigeria.
Needless to say, the issue is contentious. One of the main objections to sex selection is that it could skew the balance of the sexes. In many parts of Asia and Africa, male children are sought after. However, in western countries, the opposite seems to be true. "The vast majority of patients who come to us request girls," says Trina Leonard of the Genetics and IVF Institute in Fairfax, Virginia, which offers a sperm-sorting technique and PGD.
Many countries, including the UK and Australia, do not allow sex selection for non-medical reasons. Where it is allowed, some clinics restrict sex selection to family balancing, meaning a couple must already have a boy if they request a girl and vice versa. "You can't come here and say 'I want a family of five boys'," says Leonard. But half of the clinics in the US that carry out PGD for sex selection do not insist on family balancing, and many of their clients are couples from countries where sex selection is banned.
In the long term, it may be hard for regulatory authorities to continue to deny access to sex selection. "The reality is that the technology is available, and people want access to it," says Fishel. John Harris, a bioethicist at the University of Manchester, UK, sees no moral or ethical objection to sex selection. He suggests that a trial number of procedures should be allowed to see if fears about the social impact are justified.
How much further can selection go? What of that object of tabloid hysteria, the "designer baby"? Will we one day be able to ask for a tall, musical, blue-eyed boy or a dark-haired girl? Even if regulatory authorities allow us to use PGD to select desirable gene variants, there are major snags. For starters, IVF typically generates fewer than 10 embryos per cycle. This means parental choice will be very limited. "I don't think anyone in their right mind would ever go through IVF to select the hair colour of their offspring," says Yuri Verlinsky of the Reproductive Genetics Institute, Chicago, one of the pioneers of PGD.
"The only way to increase choice would be to generate larger numbers of eggs," says Handyside. It might become possible to do this by maturing early-stage eggs taken from the ovaries in the lab, or by generating eggs from stem cells (see The egg and sperm race). Even then, the options will still be limited. "Unless we interfere with the genes of an embryo, children are going to resemble their parents," says Handyside. "The genes for particular characteristics may not be there."
What's more, predicting which of 100 embryos will turn into the most intelligent child or the greatest athlete will require enormous advances. "If tomorrow there was a publication saying that we have managed to identify all the genes involved in intelligence, then screening for it would be available in a few years," says Fishel. "But until there is a breakthrough in our knowledge it looks improbable that we could screen for amorphous traits like that, because we do not really know what they involve."
And the choices will not always be easy. Would you opt for gene variants that boost creativity if they also increased the risk of mental health problems, for instance? For would-be parents, simply understanding the information available will be difficult and the weight of decision-making will be far heavier. Even the decision not to screen will be a fraught one. It would be sad if this burden came to overshadow the thrill and wonder of bringing a new life into the world.
On the other hand, if screening for IQ does become possible there could be huge demand for it. Like it or not, we will be faced with new reproductive options - if societies choose to allow them. "We are going to have the technical ability to look at a very fine scale at the genetics of embryos in vitro and in pregnancy," says Handyside. "There are huge challenges for society to adapt and to work out where we should draw the line, what we should be looking for and what we should do with this information."
The battle over how this technology is used will shape the way future generations reproduce. The ethics of embryo selection will be pitted against the ethics of denying it to people who want it. Yet according to Harris, this is a false dilemma. "No embryo has a right to be implanted, and a woman has no obligation to have any embryo implanted if she does not want to," he says. "She makes a choice about which embryo, if any, to accept. I cannot see any justification for her being denied the information to make that choice rationally."
"There should be no restriction on using PGD for diagnosing disease," says Verlinsky. "Everyone wants to protect their children; nobody wants to see them go through the same horror that someone else in their family did."
If people continue leaving childbirth ever later in life, there is no doubt that increasing numbers will have to resort to IVF. The growing advantages of PGD may persuade more and more fertile couples to join them. So will old-fashioned sex ever fall out of favour as a way of making babies? It is certainly not going to happen in the next 10 or 20 years, but in the next 50 or 100 - who knows? After all, who would have predicted how common IVF would become back in 1977, when Louise Brown was just a speck in a Petri dish?
Jargon buster
IVF
Used here to refer to any form of fertilisation outside the body. Doctors, however, distinguish between conventional IVF - placing sperm with an egg in a dish and leaving them to it - and ICSI (intracytoplasmic sperm injection), where a single sperm is injected into an egg.
PGD
Pre-implantation genetic diagnosis. The testing of IVF embryos before implantation by removing one or more cells for analysis. Also refers to the testing of eggs before fertilisation. Not to be confused with prenatal testing during pregnancy.
IVM
In vitro maturation. A new method that involves collecting immature eggs and maturing them outside the body, instead of using drugs to stimulate women to produce many mature eggs. Its safety is not yet clear.
In vitro figures
30,000 IVF children were born worldwide in 1989 and at least 200,000 in 2002
Well over 3 million children worldwide have been conceived by IVF since 1978
In Denmark and the Netherlands 1 in 25 babies are conceived in a dish
A window on the womb
You don't have to resort to IVF-PGD to screen for genetic disorders. Tests can also be carried out during pregnancy. Obtaining fetal cells involves invasive procedures that can trigger miscarriages, however, so such tests are usually done only if scans reveal an abnormality or if there's a high chance of a child inheriting a serious disease. Prenatal screening is also routine to confirm the results of PGD, which will never be 100 per cent reliable.
Most tests look for major chromosomal disorders, such as Down's syndrome. In Europe more than 90 per cent of fetuses with Down's are aborted, so fewer and fewer children are born with the disorder, despite the rising number of older mothers (see "The egg and sperm race").
More wide-ranging prenatal genetic tests are becoming available. Art Beaudet's team at Baylor College of Medicine in Houston, Texas, now offers screening for more than 150 different genetic abnormalities, using a technique called array-CGH to look for parts of chromosomes that have been duplicated or deleted.
Safer, non-invasive methods, such as isolating fetal DNA or cells from a mother's blood, could lead to prenatal genetic screening becoming more common. However, some geneticists say we do not yet know enough to routinely apply tests such as Beaudet's: the amount of information such tests can yield is growing faster than our ability to interpret it. And an abnormal result will always confront parents with the agonising decision of whether or not to terminate the pregnancy.
From issue 2574 of New Scientist magazine, 20 October 2006, page 42-45
posted by JDS at 8:02 AM
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