A study of the survival rates of premature babies has provided a vital boost to pro-choice campaigners, ahead of one of the most significant parliamentary debates on abortion for a generation.

As the Human Fertilisation and Embryology Bill returns to the Commons on Monday, campaigners are preparing to use it as a battleground for reform of Britain's abortion laws, 40 years after the termination of pregnancy was made legal.

Anti-abortion MPs are demanding a cut in the 24-week time limit on the ground that some babies are viable at 23 or even 22 weeks. The group, led by the Tory MP and former nurse Nadine Dorries, claims that the lives of as many as 2,000 babies a year could be saved by a reduction in the limit to 20 weeks.

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Jim Dobbin, chairman of the pro-life group of MPs, said he would like to see the current limit halved. "We would like there to be a number of amendments where you can start from a lower limit, say 13 weeks," he said.

Dr Peter Saunders, general secretary of the Christian Medical Fellowship, said his group was supporting 20 weeks as a first step. "It gets a lot of people on board and gets us on the way," he said. "We have to realise we are in for a very long battle here."

But a new survey of all extremely premature babies born in the Trent region shows no improvement in survival of those born before 24 weeks over the past 12 years. The review of 55,000 births in 16 hospitals showed a significant improvement in survival of babies born at 24 and 25 weeks with almost half (47 per cent) of the 497 babies admitted to intensive care surviving to go home in 2000-05, compared with 36 per cent of the 490 born in 1994-99. But only 18 per cent of those born at 23 weeks – 12 out of 65 babies – survived their stay in hospital, and none of the 150 born at 22 weeks.

Professor David Field, of the University of Leicester, who led the study, said there was a "lack of evidence" to support the claim that the current limit for abortion should be lowered because of continued improvements in medical care. "The limits of viability for the survival of premature babies have been reached," he said.

The findings are in line with preliminary results from a national study, released last month, which also showed no increase in the number of babies surviving after being born within the 24-week abortion limit over the past 10 years.

The report, Epicure 2, was presented at the annual conference of the Royal College of Paediatrics and Child Health in York but has not yet been published. It examined all severely premature births across England in 2006 and found improved survival rates only in babies born after 24 weeks, compared with those born a decade previously.

Its conclusions are not likely to cut much ice with Ms Dorries, who claims the backing of almost 200 MPs ahead of next week's parliamentary confrontation. With strong backing from many Catholic MPs, pro-life campaigners believe that the tide of public opinion has turned on abortions and a majority of voters would now back a reduction of the upper time limit on the grounds that technological advances have increased the viability of early births.

According to the Tory MP, no one would have thought that, when abortion was legalised 40 years ago, it would have led to seven million abortions in Britain in the intervening years. She said: "Polling shows that 72 per cent of the public believe 24 weeks is too late. Given we know so many babies now survive that are born below 24 weeks these issues are compelling reasons why it is time to reduce it to 20 weeks."

She added that of almost 3,000 abortions carried out last year between 20 and 24 weeks, up to 2,300 might result in viable births (after excluding those where either the mother or foetus was suffering serious health problems). Abortions past 20 weeks, she said, were "not the mark of a decent society" and the process was "frankly barbaric".

Pro-choice MPs led by the Liberal Democrat Evan Harris, a member of the Commons Science and Technology Committee, will demand an end to the requirement for two doctors to give permission for an abortion which can be a "barrier" for some women seeking help, resulting in abortions later in pregnancy.

The group said reducing the time limit will close the options for the most vulnerable women, such as teenagers, who discover too late that their foetus has an abnormality. The Health minister Ann Keen has said there was "no evidence" to support a lowering of the time limit, echoing the report of the Commons Science and Technology Committee last year.

Medical organisations have urged MPs to conduct the debate with "evidence-based, factual information". In a joint statement last month, the British Medical Association; the Royal College of Obstetricians and Gynaecologists; the Royal College of Nursing; and the British Association of Perinatal Medicine said there was "no evidence of a significant improvement in survival of pre-term infants below 24 weeks' gestation in the UK" since 1990, when the time limit was reduced from 28 to 24 weeks.

Alan Johnson, the Health Secretary, has told MPs the 24-week limit has "stood the test of time" and should remain. MPs are to be given a free vote on the issue but supporters of the existing law fear they could be forced to compromise on 23 weeks, to limit any change.

Almost 200,000 pregnancies are terminated every year in England and Wales. Critics point to the steady rise in abortions as evidence of the failure of sex education and family planning. Defenders say one in three pregnancies is unplanned. Better provision of contraceptive services and easier access to abortion are key elements of a safe service, they say. Less than 1 per cent of abortions are carried out at more than 22 weeks and 87 per cent are performed before 13 weeks.

Global rules on termination

France

Since 1979 abortion has been available if it is carried out by the end of the 10th week of pregnancy and by a physician in an approved hospital. By law a woman must state she is "in a situation of distress" but in practice women can choose to have an abortion.

The Netherlands

Abortion is available on request up to 24 weeks, the point of viability, though in practice it tends to be just over 21 weeks. The Netherlands has one of the lowest international abortion rates which experts say is due to widespread use of contraception. A woman seeking an abortion must discuss her decision with her doctor who must establish it has been taken voluntarily and after careful consideration. After this, the woman must wait at least five days before the abortion can be performed if the abortion is taking place more than 16 days after menstruation was due.

Czech Republic

Abortion has remained the preferred method of birth control. A woman must make a written request to her gynaecologist for the "artificial termination of pregnancy", and the gynaecologist will then inform her of the possible consequences of the procedure and of other available methods of birth control.

Russia

Russia – where abortion is available on request with the same provisos as elsewhere for cases up to 12 weeks' gestation – has one of the highest abortion rates in the world, with an estimated 13 terminations for every 10 live births in 2003. It was the first country to legalise abortion in 1920, although the law was repealed in 1936 and abortion remained illegal until 1955. As with the Czech Republic, termination is considered to be a common method of birth control, though this appears to have changed in recent years: between 1988 and 2001, modern contraceptive use increased in Russia by 74 per cent, while the abortion rate declined by 61 cent.

The United States

Abortion is a highly contentious political issue, and the law varies from state to state. The Supreme Court in its landmark Roe v Wade decision in 1973 ruled by a 7-2 vote that women have a constitutional right to an abortion, making abortions legal throughout the nation. In 1992, the court allowed some new restrictions as long as they do not impose an "undue burden" on pregnant women.

Sources: BMA, Reuters

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