Detection Rates for Aneuploidy by First-Trimester and Sequential Screening

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OBJECTIVE:To estimate detection rates for aneuploidy by first-trimester and sequential screening.METHODS:The study included women with singleton pregnancies who participated in the California Prenatal Screening Program with estimated delivery dates from August 2009 to December 2012 who had first- or first- and second-trimester (sequential) screening. Detection rates were measured for target (trisomies 21 and 18) and other aneuploidies identified from the California Chromosome Defect Registry.RESULTS:Of 452,901 women screened, 17,435 (3.8%) were screen-positive for Down syndrome only; 433 (0.1%) for trisomy 18 only; 1,689 (0.4%) for both Down syndrome and trisomy 18; and 2,947 (0.7%) for neural tube defects, Smith-Lemli-Opitz syndrome, or for multiple conditions. The detection rates were Down syndrome—92.9% (95% confidence interval [CI] 91.4–94.2); trisomy 18—93.2% (95% CI 90.5–95.9); trisomy 13—80.4% (95% CI 73.9–86.9); 45,X—80.1% (95% CI 73.9–86.3), and triploidy—91.0% (95% CI 84.2–97.9). Overall, the detection rate for chromosome abnormalities was 81.6% (95% CI 80.0–83.1) at an overall false-positive rate of 4.5%.CONCLUSION:First-trimester and sequential screening are sensitive and specific for the broad range of karyotype abnormalities seen in the population.LEVEL OF EVIDENCE:II

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