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The aim of this study was to determine the impact on the risk calculation of various ways of handling maternal weight when these data are provided in the first part but not the second part of a sequential screening protocol.A retrospective analysis of 38 986 sequential screens was carried out in which weight was provided in both the first and second trimesters. Three potential strategies for calculating multiples of the median values when the weight is not recorded at the time of second trimester risk evaluation were evaluated. First, perform no weight adjustment. Second, use the first trimester weight. Third, use the predicted second trimester weight on the basis of the first trimester weight. To predict the second trimester weight, we used a random-effects, multi-level model.The screen positive rate for Down syndrome was 3.0% (1151/38 986) and trisomy 18 alone 0.12% (47/38 986). The three strategies resulted in 196 (0.50%), 41 (0.11%), and 23 (0.06%) patients switching risk categories with the no adjustment, first trimester weight, and predicted weight strategies, respectively.Utilizing the first trimester weight or the predicted second trimester weight in sequential screening when second trimester weight is not provided offers an affordable alternative for laboratories to provide robust risk calculations and interpretations without requiring excessive use of resources. © 2014 John Wiley & Sons, Ltd.What's already known about this topic?Maternal serum markers need to be adjusted for maternal weight in aneuploidy screening.In sequential screening, maternal weight may be provided with the first but not second blood draw.What does this study add?Utilization of the first trimester weight or prediction of the expected second trimester weight into weight adjustment formulas produces MoM and risk results similar to those observed with the actual second trimester weight.