Dutch doctors call for all pregnant women to be screened for Down's

British Medical Journal, Oct 2, 1999 by Tony Sheldon

Dutch researchers are calling for all pregnant women to be offered screening for Down's syndrome in the first trimester on the basis of ultrasound measurement of nuchal translucency and maternal serum markers in addition to maternal age.

Currently, the only legal screening programme in the Netherlands for Down's syndrome is based on maternal age. All women aged over 36 years are offered prenatal diagnostic testing by amniocentesis or chorionic villus sampling, but only 45% accept. Most babies with Down's syndrome, however, are born to younger women.

In the United Kingdom most screening for Down's syndrome is carried out by means of blood tests during the second trimester of pregnancy. Only about 10% of mothers are offered nuchal translucency screening by ultrasound, in which the subcutaneous oedema in the fetal neck is measured-abnormal swelling can indicate an increased risk of chromosomal defects. Some doctors predict that more antenatal clinics will change to first trimester screening when the results of a large scale NHS funded study become known in the new year.

Last month the Dutch health minister, Els Borst, informed MPs she had given Amsterdam's Free University permission to launch a scientific investigation into screening for Down's syndrome, and a report is due soon from government scientific advisers, the Dutch Health Council.

Pressure for change mounted with last week's publication of a study, carried out at Amsterdam's Academic Medical Centre, which achieved an expected detection rate of 85%, with a false positive rate of 5% (Prenatal Diagnosis 1999;19:458-62).

Ultrasound screening of nuchal translucency was combined with screening of maternal serum, using two markers associated with Down's syndrome: pregnancy associated plasma protein A and free human chorionic gonadotrophin.

Dr Irene de Graaf, an obstetrician carrying out research for a doctoral thesis on screening in the first trimester, asked all women undergoing invasive prenatal diagnosis at the centre between 1994 and 1997 to participate.

Blood samples and ultrasound recordings were examined from 37 women whose babies were found to have Down's syndrome, together with samples from 255 controls.

Using statistical modelling an expected detection rate of 55% was achieved when using maternal serum alone, 68% for ultrasound screening of nuchal translucency alone, and 85% when the two were used together. Results among the Dutch population are comparable to those in the United Kingdom and United States (New England Journal of Medicine 1998;338:955-61; Lancet 1998;351:343-6).

Researchers also carried out a survey of women's opinions, and about 70% expressed a preference for combined serum and ultrasound screening in the first trimester.

In her doctoral thesis, Dr de Graaf argued that prenatal diagnosis could be more efficiently offered to women at risk if prenatal screening was offered to all women. She said that further research was now needed to confirm their results.

"We could introduce screening on a research basis as part of a large scale prospective study," she added.