Down's Syndrom Screening: A Case Study in Decision Making

Read "Pre-natal testing: Wanted: perfection" in The Economist, July 5, 2007. (Subscription required.)

The article, subtitled "Doctors try not to be sued over Down's syndrome babies" summarizes the changes in guidelines for prenatal screening of pregnant women to detect fetuses with Down's syndrome. Mew guidelines published in January by the American College of Obstetricians and Gynaecologists urge that all pregnant women, regardless of age, should be screened for babies with Down's syndrome.

Pregnant older women have a higher risk of Down's Syndrome affecting their babies, but there is a risk in any pregnancy; 80 percent of Down's syndrome babies are born to women under the age of 35. Pregnant women may be screened to detect Down's Syndrome "through blood tests and ultrasound scans, then with amniocentesis or chorionic villus sampling......The new recommendation is that all women be screened at the 20th week, using the same tests; and many women are being pushed to have them earlier." In the past full screening was standard for older women in the first trimester, but younger women have been screened too, but often "in their second trimesters and only with blood tests". The full tests are more accurate (amniocentesis has a 99% accuracy rate). Both amniocentesis and CVS tests carry a slight risk of miscarriage. Roughly 80% of women testing positive for Down's under the current system have abortions. Currently, some 350,000 Americans have Down's syndrome.

Comment: Of course, there is no reason for a woman to be screened if she and her family would consider no action as a result of the information provided by the screening. A general rule of medicine is not to screen if you will not utilize the information provided by the screening, since there would be a cost and a risk (however slight) associated with the screening.

Guidelines for screening should change as:

• The risks associated with the screening tests change;
• The costs of screening change;
• The screening techniques are improved;
• The willingness of patients to act on the screening results changes;
• The cost and safety of interventions based on the screening information change;
• The ability of the health system and/or patients to pay for the screening and post-screening interventions changes.

Of course, guidelines are just guidelines. An individual should have the right to choose whether to follow the guidelines or not. The evaluation of the risks and benefits of screening done by the medical association are based on the population as a whole, and an individual may be more or less risk adverse than average, have greater or lesser risk due to her overall medical condition than average, have different than average propensity for medical interventions, and have strong views on the morality of the intervention and its result. JAD