Objective: This study aimed to construct a measure of informed decision making that includes knowledge, deliberation, and value-consistency, and to assess the level of informed decision making about prenatal screening, and differences between test acceptors and test decliners. Methods: Women attending one of 44 midwifery and gynaecology practices were asked to fill out postal questionnaires before and after the prenatal screening offer. The principal outcome was the level of informed decision making. For this purpose, knowledge about prenatal screening, deliberation about the pros and cons of the alternatives, test uptake, and attitude towards having a prenatal screening test were measured. Results: Eighty-four percent of the participants were sufficiently knowledgeable about prenatal screening, 75% of the decisions were deliberate, and 82% were value-consistent. Fifty-one percent of the participants made an informed decision. Test acceptors made less informed decisions as compared to test decliners. This difference was mainly caused by the lower rate of deliberation in this group. Conclusion: It appears from this study that prenatal screening decisions are often not informed decisions. This is inconsistent with the main objective of offering screening, which is to enable people to make informed decisions. Practice implications: Decision makers should be encouraged during the counselling to deliberate about the various alternatives.