The impact of maternal weight discrepancies on prenatal screening results for Down syndrome

This study aimed to assess the quantitative impact of maternal weight discrepancy on the screen result for Down syndrome when using Integrated Prenatal Screening and First Trimester Combined Screening.The study population consisted of 78,165 women undergoing prenatal screening in Ontario, Canada, and 158 pregnancies affected with Down syndrome at one Ontario center. The study assessed quantitative alterations of the multiple of the median values of first and second-trimester serum markers and the risks of Down syndrome at a set of theoretical weight discrepancies.Weight discrepancies have the greatest impact on screening results when the initial risk is close to the risk cut-off. When the weight discrepancy is 5 lb or greater and the denominator of the initial risk is within 50 of the risk cut-off, the chance that a screen result will change from positive to negative or from negative to positive is 47-55% for women undertaking Integrated Prenatal Screening. This chance is 33-43% for women undertaking First Trimester Combined Screening.A weight discrepancy of five or more pounds has a significant impact on the risk of Down syndrome; correction of maternal weight would improve the accuracy of the screening test.