New ultrasound and blood tests offer hope for more effective and less invasive detection of chromosomal abnormalities

New ultrasound marker
An accurate, non-invasive Down's syndrome screening test for pregnancy is the Holy Grail of preventative foetal medicine. Now nuchal translucency pioneer Professor Kypros Nicolaides has discovered a new marker for Down's that can be detected by ultrasound in the first trimester. The majority of Down's foetuses in a study of 701 pregnancies lacked a nasal bone.

Amniocentesis news
Over the last 20 years, there's been a steady increase in the efficiency of screening tests for chromosomal disorders. To begin with, mothers were screened only for age or family history. Later, a range of markers in the mother's blood could be measured for risk. If the result was positive, then the mother would be offered amniocentesis, where amniotic fluid is drawn from the uterus through a needle around week 16, or chorionic villius sampling (CVS), where a sample of the developing placenta is removed around week 11.

'This results in around 300 miscarriages a year, mostly of healthy babies,' says Nicolaides. When the statistics were examined this year, it was discovered that, for every baby with a disability detected by invasive tests, four healthy babies were lost to miscarriage.

Following retrieval, foetal cells had to be cultured, and results would not be available for two weeks, adding to the stress of parents. A new procedure, called quantitative fluorescence polymerase chain reaction (QF-PCR), has speeded up results to around 1.25 working days, but is not widely available.

Down's inspiration
When he originally described Down's syndrome in 1866, Dr John Langdon Down noted that the skin of affected people seemed too big for their bodies. This observation prompted Professor Kypros Nicolaides to develop the nuchal translucency ultrasound screening test, that measures a fluid filled area at the back of the foetal neck. Down's other observation - that they had small noses with a flat bridge - has now inspired the new ultrasound screening test to check for nose bones.

During research that ended in October 2001, a sample of 701 pregnant women, considered to be high risk due to their age and nuchal translucency results, were offered another scan between 11 and 14 weeks to examine the foetus's profile. All the women then went on to have CVS or amniocentesis. The scans detected that 73 per cent of Down's foetuses had no nasal bone, compared to 0.5 per cent of foetuses that were chromosomally normal.

More effective blood tests
In a separate development, Professors Dennis Lo and James Wainscoat of Oxford University have succeeded for the first time in reliably identifying foetal DNA in maternal plasma. The rights to develop a test based on the discovery were snapped up by BTG, a UK technology transfer company which hopes that it will prove as reliable for detecting chromosomal disorders as amniocentesis and CVS, but without the risk of miscarriage. The test should be available within five years.

Benefits of the new tests
Both new tests would be cost effective for the NHS, as they require no new procedures or special equipment. Amniocentesis and CVS cost the NHS £250 a time which currently adds up to £5 million a year.'If doctors spent an extra few seconds while the woman is having a routine scan checking for the nasal bone, it would reduce the number of invasive tests from 30,000 to 10,000,' says Nicolaides.Four out of five pregnant women opt for screening tests; and 95 per cent with positive results for abnormalities choose to accept therapeutic abortion. The new tests promise women more accurate results and less worry during pregnancy.