A new technique to select a baby’s sex appears to be safe and about 80% effective, a study suggests.
Researchers used a technique to separate sperm on whether they had an X chromosome (making female offspring) or a Y one (male offspring).
Sperm with an X chromosome are slightly heavier than those with a Y, the research indicates.
However, the study has again raised long-held concerns over the ethics of such a process.
Selecting embryos without reasons such as a sex-linked disease is illegal in many countries.
Experts behind the research, from Weill Cornell Medicine in New York, said their technique was inexpensive and “extremely safe”.
The small study involved 1,317 couples, with 105 men in the group that used the sperm sorting process.
Fifty-nine couples wanted a girl and it resulted in 79.1% (231 out of 292) female embryos, with 16 girls being born without any abnormalities.
Fifty-six couples wanted a boy and the technique produced 79.6% male embryos (223 out of 280), resulting in 13 healthy male babies.
Professor Gianpiero Palermo, one of the authors, called it “extremely safe as well as efficient, inexpensive, and ethically palatable”.
However, some experts have expressed serious concerns despite the technique’s apparent effectiveness.
Dr Channa Jayasena, head of andrology at Imperial College London, said “their technical achievement is insignificant compared to the serious ethical concerns raised by the research”.
“They propose sperm selection as an ‘ethical’ alternative to embryo selection,” he said.
“I find this incredible since sperm selection is just another way of selecting embryos to manipulate the sex of offspring, with detrimental societal implications.”
He said regulation was urgently needed to control such developments, adding that it could be adapted in future to choose traits such as skin or eye colour.
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Darren Griffin, professor of genetics at the University of Kent, also said sex selection was “ethically fraught”.
“Separating sperm beforehand may provide a legal loophole in some countries but not the UK,” he said.
“There have been numerous methods around for decades, some effective but potentially harmful, others dubious in their effectiveness.
“The current paper seems to have found a method in which the approach is effective to some degree…
“I am convinced that the science is sound and that, instead of the usual 50:50 ‘coin toss’ then a couple can get a baby with the desired sex a little under 80% of the time.”
The study is published in the PLOS ONE journal.