The human foetus cannot feel pain before the age of 24 weeks so there is no reason to change the current abortion limit, health experts said today.
Nerve connections in the brain are not sufficiently formed to allow pain perception until after the official 24-week limit for terminations, a government-commissioned report found.
The study, carried out by members of Royal College of Obstetricians and Gynaecologists, also said the foetus was in a state of "continuous sleep-like unconsciousness or sedation" even after 24 weeks.
This could mean that late abortions, which are permitted for serious abnormalities or risks to the mother's health, may not result in foetal suffering.
The landmark findings comes amid efforts by some MPs - including Prime Minister David Cameron - to lower the abortion limit.
A fresh analysis of evidence for foetal pain was recommended by MPs from the Commons Science and Technology committee during the last parliament.
On the issue of pain perception, the Royal College report concluded: "It was apparent that connections from the periphery to the cortex are not intact before 24 weeks of gestation and, as most neuroscientists believe that the cortex is necessary for pain perception, it can be concluded that the foetus cannot experience pain in any sense prior to this gestation."
It added: "There is increasing evidence that the foetus never experiences a state of true wakefulness in utero and is kept, by the presence of its chemical environment, in a continuous sleep-like unconsciousness or sedation."
Professor Allan Templeton, president of the Royal College and who chaired the inquiry, told The Times: "There's nothing in the report that suggests any need to review the upper limit."
A second report by the college, into abortion for foetal abnormalities, looked into what mental and physical abnormalities could result in a "serious handicap".
Around 1% of abortions are carried out on these grounds, taking place after the 24 week limit.
Some campaigners have demanded greater clarity following reports of late abortions for correctable conditions such as cleft palate.
But the Royal College said it was impractical to produce a list of conditions for serious handicap because it was too difficult to predict the long-term impact of an abnormality on a child or their family.
Mr Cameron said in April this year that the time-limit for abortions should be cut to "20 or 22 weeks".
The Tory leader backed a cut to 22 weeks in 2008, when the House of Commons voted to keep the existing maximum of 24 weeks.
He also indicated that Conservative MPs would be allowed a free vote on the question, as is normal with issues of conscience.
Anti-abortion groups said the Royal College report did not challenge other arguments for a lower limit.
Josephine Quintavalle, of Comment on Reproductive Ethics, said: "Performing abortion humanely does not justify the fact that you are terminating a human life."
A spokesman for the Department of Health said: "We welcome any report that adds to our understanding of foetal development."
Anne Quesney, international policy and parliamentary adviser at Marie Stopes, welcomed the research.
"The RCOG's findings should give comfort and reassurance to any woman who finds herself in the extremely distressing position of having to make the decision to terminate a pregnancy at a later gestation," she said.
"Later abortions are extremely rare. In 2009, for example, abortions above 20 weeks gestation represented just 1.47% of the total carried out in England and Wales, less than 3,000 cases.
"Of these, only 1,230 cases (0.65%) were performed at 22 weeks or over.
"Later abortions are carried out for the most compelling reasons, such as severe foetal abnormality, risk to the health or life of the mother, or following a drastic change in the personal circumstances of the woman involved."
A Downing Street spokeswoman said today: "The Prime Minister's view is that he will be led by the science."
She added: "At the moment there are no plans to change the policy."
Ann Furedi, chief executive of the British Pregnancy Advisory Service (BPAS), which provides abortions, said: "This guidance on the state of the evidence is extremely welcome.
"The issue of foetal pain experience has been politicised by campaigners in a way that has inhibited a sensible discussion.
"Women and doctors need to be able to make informed decisions based on what science says, not what advocates (whether pro-choice or anti-choice) wish it said.
"This report makes it possible for choices about treatment to be properly informed."Reuse content