High resolution scans can now detect major foetal abnormalities just 10 to 14 weeks into a pregnancy - up to nine weeks ahead of normal.

They are given as routine in some hospitals, but many women are not told beforehand that they could be about to receive bad news.

Instead they see the scan as a means of telling the exact date the baby is due and whether they are expecting more than one child.

No time to decide

Writing in the British Medical Journal, Anne McFayden, a senior lecturer at the Royal Free and University College Medical School in London, said: "Most women are enthusiastic about having an ultrasound scan, perhaps because they do not associated scans with screening.

"Not all women want to know if their baby is abnormal and not all women will choose to terminate their pregnancy if it is.

"Women at high risk who are undergoing more invasive antenatal screening, such as amniocentesis, usually have time to think about the decision to take up screening, but women having an early high resolution scan may have much less opportunity for such thinking."

But some doctors say it is vital women are given as much news about their pregnancy as early as possible.

Psychological support

Guy Nash, a consultant obstetrician from East Sussex, said: "If information was not given, the mother would probably sue her obstetrician when it became known that the abnormality had been detected earlier."

The article argued women should be given a clear understanding of antenatal screening, more psychological support during the process, and improved counselling following a termination of a pregnancy.

Mary Newbone, director of policy for the National Childbirth Trust, said early stage scans should be stopped until proper scientific evaluation was carried out.

She said: "It is very important not to introduce new treatment without proper evaluation first, and that should include the psychological and social effects as well as any improved outcome in terms of pregnancy."

The use of early stage scans is currently being evaluated by an expert committee established by the Department of Health.