First-Trimester Screening for Down Syndrome with Serum Sampling at Different Gestational Ages: The Effect on Screening Performance

Introduction: The objective of this study was to evaluate the performance of first-trimester Down syndrome (DS) screening with serum sampling at different weeks of gestation. Material and Methods: We studied 35,431 singleton pregnancies (2005-2011), including 145 DS cases. Screening performance was determined in different maternal age groups with serum sampling between weeks 9 + 0 and 13 + 6. Results: No significant differences were found between the detection rates at different gestational weeks. The false-positive rate (FPR) in week 9 (6%) was comparable to the FPR in week 10 (6.5%; p = 0.214), whereas it was significantly lower compared to weeks 11 (7.2%; p = 0.007), 12 (7.4%; p = 0.003) and 13 (8.5%; p < 0.001). The odds of receiving a false-positive result was significantly increased with serum sampling in week 11 (OR 1.32, 95% CI 1.08-1.63; p = 0.008) for women >= 36 years and from week 12 onwards (OR 1.28, 95% CI 1.01-1.61; p = 0.04) for women <36 years. There were no differences in mean log(10) multiple of the median values of pregnancy-associated plasma protein-A, free beta-human chorionic gonadotrophin or nuchal translucency between both age groups, nor in mean maternal age between the different gestational weeks in either age group. Discussion: Early serum sampling (<11 weeks) resulted in higher screening performance. The impact of the increase in the FPR was highest in women >= 36 years. (C) 2014 S. Karger AG, Basel