The implementation of innovative medical technologies can raise unprecedented ethical, legal and social dilemmas. This is particularly so in the area of antenatal screening, which is dominated by the language of risk and probabilities. Second trimester serum screening for Down's syndrome and neural tube defects has a well-established place in antenatal care. Increasingly, first trimester screening with biochemical and ultrasound markers is being proposed as advance on this, yielding higher detection rates of Down's syndrome at an earlier gestational age. This article explores the experiences of 14 women offered innovative first trimester screening, which takes place within the context of a detailed ultrasound scan. The study is set within the UK, where recent policy changes mean that the offer of screening for fetal anomalies, particularly Down's syndrome, will become a routine part of antenatal care and offered to all pregnant women. This paper focuses on the significance of the scan in first trimester screening, and some of the potential dilemmas for women that can result from this. It then discusses the ways in which women made their decisions about screening, in particular, their work as 'moral pioneers'. We found that the part played by the ultrasound scan in first trimester screening, particularly in relation to the higher-quality images now being obtained, has the potential to introduce new and novel ethical dilemmas for pregnant women. Although concerns have been raised about pregnant women viewing ultrasound scans as benign, many of the women reported having thought carefully through their own moral beliefs and values prior to screening. It seems that whatever other implications they may have, first trimester screening technologies will continue the tradition of pregnant women acting as 'moral pioneers' in increasingly complex settings.