Detection Rates for Aneuploidy by First-Trimester and Sequential Screening

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.