AbstractBackgroundHere we study the levels of ADAM12s prior to and after 10 weeks of gestation to establish further the effectiveness or otherwise of ADAM12s as an early screening marker.Materials and MethodsSamples collected as part of routine first‐trimester screening were retrieved from storage at − 80 °C. In total, 55 samples from pregnancies with trisomy 21 were identified, 31 collected between the 6th and 9th weeks of gestation and 24 collected after the 10th week. A series of 567 gestational age‐matched samples collected during the same period formed the control group.ResultsThe median, multiples of the median (MoM) ADAM12s, at a median gestation of 10.0 weeks was 0.66, which was significantly lower than in the controls (p = < 0.001) when compared by Mann–Whitney test. The median MoM in those cases (n = 31) collected prior to 10 weeks was 0.618 MoM at a median gestation of 9.1 weeks. In those collected prior to 9 weeks (n = 14) the median was 0.596 at a median gestation of 8.6 weeks.ConclusionsThe data from this study does not support data from a previous study showing ultra‐low levels of ADAM12s in pregnancies affected by trisomy 21 prior to 10 weeks of gestation. Copyright © 2008 John Wiley & Sons, Ltd.