Case 1

Sarah is a 35-year-old teacher. She has two daughters, 7 and 9 years of age, from her first marriage. Her second husband Tom is 42 years old and has no children of his own. Sarah is now pregnant at 17 weeks. The first visit to the maternity clinic took place at 11 weeks, and during that visit Sarah was told about serum screening for Down syndrome. The nurse described the syndrome and the screening procedure briefly and gave her a leaflet that presented the same issues in more detail.

At home Sarah and Tom studied the leaflet together and decided that she should have the screening test. Two weeks later the test was performed, and Sarah received the results during her next visit to the clinic.

The nurse explained to Sarah that her chances of having a baby with Down syndrome were 1 in 150. She also explained that, therefore, Sarah was considered to belong to a high-risk group and that a definitive diagnosis was possible though amniocentesis. However, the procedure itself would increase the risk of miscarriage by 1%.

At home Sarah explained the result to Tom and the dilemma they were now facing. If the risk estimate was valid, there was a 99.3% chance that the foetus did not have Down syndrome and a 0.7% chance that it did. If they wanted to be sure, the option was to undergo amniocentesis, but it would slightly increase the risk of miscarriage.