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Prenat Diagn. 2014 Aug;34(8):753-8. doi: 10.1002/pd.4360. Epub 2014 Apr 30.

Extrapolation of maternal weight in sequential aneuploidy screening.

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PerkinElmer Labs/NTD, Melville, NY, USA.



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.

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