ObjectiveTo investigate to what extent a newly revised educational pamphlet on triple-marker screening improves patient knowledge and to identify subgroups of women who may not benefit from these materials.MethodsWomen in six geographically and demographically diverse Ontario sites were allocated randomly to receive the pamphlet on triple-marker screening or a similarappearing educational pamphlet on daily activities during pregnancy. The primary outcome measure was the Maternal Serum Screening Knowledge Questionnaire, a previously validated 14-item scale.ResultsBaseline demographic, obstetric, and medical factors were comparable in the intervention and control groups, as were measures of previous exposure to triplemarker screening. Knowledge scores were significantly higher among the 133 women receiving the intervention pamphlet than among 64 women who received the control pamphlet (0.89 versus 0.52 on a scale from −2 to +2,P<.001). Subgroups not benefiting from the pamphlet on triplemarker screening were women age 25 and younger and those not speaking English at home. Those who had completed university or postgraduate education had high levels of knowledge with and without the pamphlet.ConclusionWritten patient information can contribute in an important way to patient knowledge about triple-marker screening. Providers of antenatal care should be made aware of the value of written patient information as well as the limitations for some subgroups of women. These subgroups are likely to require additional educational materials and resources. It would be appropriate to make these materials available to the general public and pregnant women in their physicians' offices.