The purpose of this study was to determine the ability of pregnant women to incorporate sophisticated screening information about risk assessment into their decisions about invasive testing in an appropriate way.

Assessment of risk for trisomy 21 was carried out by a combination of maternal age, fetal nuchal translucency (NT) thickness, and maternal serum free β-human chorionic gonadotrophin (hCG) and pregnancy-associated plasma protein-A (PAPP-A) at 11 to 13+6 weeks. The patients were counseled with regards to their estimated risk, and were informed that the only way to know for sure whether or not the fetus has a chromosomal abnormality is by having an invasive test, but these tests carry a risk of miscarriage of about 1%. They were also informed that although a risk of 1 in 300 or more was generally considered to be high, it was up to them to decide in favor or against invasive testing.

Assessment of risk was carried out in 30,564 singleton pregnancies with live fetuses at 11 to 13+6. The median maternal age was 34 (range 15-49) years and, in 14,816 (48.5%), the age was 35 years or greater. The rate of invasive testing increased exponentially with increasing estimated risk (r=0.917, P < .0001). The estimated risk for trisomy 21 was 1 in 300 or more in 2565 (8.4%) women, and 1991 (77.6%) of these had invasive testing. The risk was less than 1 in 300 in 27,999 (91.6%) women, and 1286 (4.6%) of these had invasive testing.

Pregnant women are able to use sophisticated screening information to make scientifically and ethically rational decisions about invasive testing for trisomy 21. These empiric data compliment the arguments of normative ethics to create evidence-based ethical standards for informed consent regarding invasive testing.