It is an emotional moment especially for first-time mothers-to-be. When they see the mysterious moving form of their baby on the ultrasound screen, they are overwhelmed. Suddenly, the baby becomes a physical reality. Unfounded fears of abnormalities are allayed. Some even walk away with snapshots of the unborn child. No parent wants to miss this moment of joy. Even Dr Lam Man-ying, who has herself seen many images of babies as senior medical officer of obstetrics and gynaecology at the public Pamela Youde Nethersole Eastern Hospital. 'I had three scans when I was pregnant with my first child. I just kept going back for more because I wanted to see my child,' said Dr Lam. Dr Lam gave birth to a daughter, and she is currently six months pregnant. She has had a miscarriage between the two pregnancies. 'When I saw the image of my second child, I felt very relieved. The image shows the baby is viable. It is growing. I guess all mothers, especially those who have experienced a miscarriage, feel the same.' Scans were first devised in the mid-1950s as a means of examining foetuses, and nowadays virtually every pregnant woman has at least one; some have as many as 10. At Dr Lam's hospital, routine ultrasound scanning is offered to all mothers between the 18th and 20th weeks. Some public hospitals only offer it to mothers who have shown problems. Ultrasound uses echo to locate an object. Soundwaves are emitted from a hand-held scanner, and as it is moved over a woman's abdomen, the sound is reflected back as echoes and transmitted to a computer to build up an image on screen. This simple, non-invasive technique allows a doctor to detect the number of babies, the position of the placenta, growth rate and any gross abnormalities. The trend is for antenatal scanning to be offered to all mothers as doctors believe it plays an important role in lowering the incidence of peri-natal mortality. But concern over the safety of ultrasound and its effect on the foetus refuses to go away. A number of studies have not only questioned the benefit of routine scanning, but also suggested it carried an element of risk on the delicate foetus. The British campaign group AIMS (Association for Improvements in Maternity Services) has suggested that the rising incidence of language delay in children might be the result of ultrasound exposure in the womb. A long-term study of more than 1,000 children, reported widely earlier this year, found that one in five had speech problems. Dr Sally Ward, the speech therapist who carried out the study, blamed the high incidence on parents who sat their toddlers in front of the television for long periods rather than talking to them. But AIMS said that a Canadian study carried out in 1993 suggested a different factor might be at play. The study shows children with speech delays were twice as likely as other children to have been exposed to prenatal ultrasound. The researchers said that if there was no obvious need for ultrasound, 'physicians might be wise to caution their patients about the vulnerability of the foetus to such noxious agents'. Two other studies have also cast doubts on the safety of ultrasound. The first, published by a group of Australian researchers in the British medical journal The Lancet, found a possible link between repeated exposure to very high-intensity ultrasound as in the Doppler scanner - which is used in Hong Kong, although not as frequent as the common ultrasound scanning over the belly - and reduced birth weight. The second study, published in the British Medical Journal by researchers at a Norwegian university, claimed that ultrasound scanning appeared to cause more children to be born left-handed. Researchers followed up children aged eight and nine who received scans between 1979 and 1981, and compared them with children who had not. There were no signs of neurological damage but researchers found that children who had been scanned in the womb were 30-per-cent more likely to be left-handed. AIMS points out that if scanning is linked to handedness, this means it affects the developing brain of the foetus. But Professor Constantine Metreweli, head of the department of diagnostic radiology and organ imaging at the Chinese University, dismisses the Norwegian findings on handedness. He said that the study should be tested further because it didn't take into account the fact that many children were forced to correct their left-handedness. 'I am sceptical about the study on speech delay and things like that. My opinion is there is no evidence whatsoever at the moment to show definite harm to the foetus or embryo,' he said. Participants in the debate have, however, questioned certain aspects of the use of ultrasound. They express disquiet over the use not of regular scanning machines on bellies, but of the more powerful Doppler scanner, which can track the movement of red blood cells. In pregnant women, it can be used to check blood flow through the umbilical cord. Professor Metreweli agrees that the Doppler scan should be used only when necessary during the first trimester, but added: 'The levels which we are using in clinical practice . . . are set to give a safe level.' He said that there was 'absolutely' no problem for a pregnant woman to have an ultrasound scan every four weeks. He also endorses the use of the so-called 'transvaginal' scanning method. In this technique a probe is inserted into the woman's vagina. Professor Metreweli said it was one of the best ways to detect abnormalities early on during pregnancy. Professor Metreweli recommends a transvaginal scan during the first trimester to pick up chromosomal defects like Down's syndrome, and a normal, or transabdominal scan for anomalies at week 18 and another to check on growth at week 30. He recommends another scan beyond week 30. 'Very few centres will do a complete scan on babies once they are born. But if the mother is scanned at the 35th week, important things could be picked up. 'About 15 years ago, we saw a lot of chronic renal failure in five-year-old children in the UK. If they had had a scan done beyond 30 weeks, the problem would have been picked up and they would not have died of renal failure later. 'For the majority of mothers, the scan may not be of any benefit, but if you are the mother and something is picked up, you will be very grateful.'