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Connor, a healthy baby boy, has made history. He is the first child to be born after his parents had the entire genomes of a batch of their IVF embryos screened for abnormalities, with the intention of picking the healthiest for implantation.

The technique could increase the number of successful pregnancies from IVF. And although the researchers stopped short of actually sequencing the boy鈥檚 genome, the advance is proof that this could be done 鈥� potentially ushering in an era of designer babies.

IVF accounts for between 1 and 5 per cent of all births in developed countries, but it is very inefficient. An estimated 80 per cent of embryos either don鈥檛 implant or miscarry, while only a third of IVF cycles result in a successful pregnancy, largely due to abnormalities in the number of chromosomes an embryo possesses.

鈥淚f you take a woman in her early 30s, around a quarter of her embryos will be abnormal. For a woman in her early 40s, it鈥檚 around three-quarters,鈥� says at the University of Oxford, who pioneered the new technique. The problem is that many abnormal embryos look normal under a microscope. 鈥淲e need better ways of working out which embryo is the one that we should implant,鈥� says Wells.

To do this, he first took cells from seven 5-day-old embryos and extracted their DNA. He then used a technique called next-generation sequencing (NGS) to assess the number of chromosomes in each cell. This involves breaking the DNA into fragments that a computer then reads and predicts where on the chromosome each fragment came from. The sequence of an entire genome can be read in this way 鈥� although Wells鈥檚 team didn鈥檛 do this. They were merely interested in the proportion of DNA coming from each chromosome.

DNA library

In earlier studies, the team had compared the DNA fragments produced using NGS from healthy cells, those taken from abnormal embryos and those taken from cells with known chromosomal abnormalities. These were used as a library against which the DNA from the seven embryos could be compared.

Of the seven embryos, three were found to be normal, and one was implanted into the mother, resulting in the birth of Connor in Pennsylvania last month (see 鈥淢aking a baby the scientific way鈥�). A second woman is also expecting a baby after undergoing the same process. Neither woman has a history of inherited disease, they merely wanted to maximise their chances of having a baby through IVF.

The hope is that by selecting only healthy embryos for implantation, more women will become pregnant and fewer will experience miscarriages. Recent clinical trials of a related technique called pre-implantation genetic screening have suggested that the method could boost the implantation rate by around a third, while the miscarriage rate could be halved. The big advantage of using NGS is that multiple embryos could be screened simultaneously, significantly reducing the cost.

鈥淭his isn鈥檛 going to solve the problem of reproductive ageing, as a couple in their early 40s may find they have no healthy embryos from which to choose,鈥� says Wells. However, it should boost the success rate for IVF in younger women, and also avoid the storage of embryos that have no chance of growing into a healthy baby.

The technique can also be tweaked to allow mutations in any gene of interest to be examined, such as those that cause cystic fibrosis. 鈥淭his potentially gives us the opportunity to look at multiple genes and chromosomal copies,鈥� says Stuart Lavery, director of IVF Hammersmith, one of the UK鈥檚 largest IVF units. 鈥淚t gives us a very powerful tool for pre-implantation genetic diagnosis.鈥�

Misuse potential

However, the fact that NGS can be done on a single cell from human embryos also raises the potential for misuse. Last year, researchers in the US sequenced the entire genome of an 18-week-old fetus using fragments of fetal DNA in the mother鈥檚 blood along with DNA samples from both parents. Wells鈥檚 technique shows that it鈥檚 possible to do this far earlier 鈥� before an embryo has even implanted in the uterus.

鈥淚t shows that there is the potential for getting an unprecedented amount of information about an embryo before it鈥檚 transferred to the womb,鈥� says Wells, who presented his technique at the annual meeting of the in London today. 鈥淲e need to be very careful that this isn鈥檛 used for trivial, non-medical reasons.鈥�

Earlier this year, Dutch researchers published a paper suggesting that eye and hair colour can be predicted from a DNA sample (Forensic Science International, DOI: 10.1016/j.fsigen.2012.07.005), and they are now using such tests to help police identify suspects or victims of crime. The same group is also developing tests to predict the shape of facial features, such as prominent cheekbones or a large nose, and complexion.

鈥淔or now, eye and hair colour are the only appearance traits that can be predicted from DNA with any practically useful accuracy,鈥� says of Erasmus Medical Centre in Rotterdam, the Netherlands, who led the research. 鈥淪ome of the available tests are very sensitive and work from a small number of cells provided that the DNA is not heavily degraded. However, the fact that something is scientifically and technically possible doesn鈥檛 necessarily mean that it should be done.鈥�

Designer babies

In the UK, genetic testing of embryos is strictly regulated, but this isn鈥檛 the case in other countries such as the US.

鈥淎t some point in the not too distant future, prospective parents will have the technical ability to look at the genome of their embryos and select embryos based on the traits they see, whether those are disease traits, cosmetic traits, behavioural traits, or boy or a girl,鈥� says , director of the Center for Law and the Biosciences at Stanford University in California.

What鈥檚 more, enforcing a worldwide ban on such genetic selection might be unworkable, says Greely. 鈥淭here are roughly 200 countries in the world. If 199 ban it, that鈥檚 a great commercial opportunity for the 200th,鈥� he says.

Even so, Wells thinks there are several reasons why using this technology to create designer babies is unlikely to catch on. The first is that couples only tend to produce a limited number of embryos, and all of them carry their own genetic characteristics.

鈥淭wo people who are both 5 foot 2 tall are unlikely to produce a basketball player,鈥� he says. And the more traits a couple tried to select, the more embryos would be eliminated. Pick more than one or two traits, and there may be no more embryos left to choose from. 鈥淭o go through all the difficulties, expense and uncertainty of an IVF cycle to choose something trivial, I can鈥檛 see many people doing it,鈥� Wells says.