711: Adverse perinatal outcomes in euploid pregnancies with double-positive first trimester prenatal screening for Trisomy 18 and 21

Abstract

were selected for testing because they are not easily detectable by karyotype, their cumulative frequency is substantial, and they are not usually associated with abnormal ultrasound (US) findings. STUDY DESIGN: Clinical prenatal samples (n 80) were referred to our laboratory for testing with this assay using specimens derived from amniotic fluid and chorionic villi. All samples tested were also karyotyped. Indications for study included AMA (30/80), AMA with a positive family history (4/80), AMA with an abnormal maternal serum screen (MSS) (13/80), abnormal fetal US findings with AMA, family history, and/or abnormal MSS (12/80), abnormal fetal US findings only (11/80), family history alone (2/80), abnormal MSS alone (6/80) and anxiety non-AMA (2/80). RESULTS: For our first 80 prospective specimens, the assay detected abnormalities in 7 cases: 2 Tri-18, 3 Tri-21, 1 each of deletion 1p36 and 5p15. One case with a normal result had 69,XXX by karyotyping. One case with an ambiguous result due to maternal cell contamination had 45,X in 18/19 cells by karyotyping. The mean turnaround time was 1.85 days. Overall, our detection rate of abnormal findings utilizing this assay and karyotyping is 12.5% and a 2.5% detection rate for microdeletions that would have been missed by karyotyping. CONCLUSION: Our results suggest that this new rapid assay, which is designed to avoid detection of results of unclear clinical significance, is a viable alternative to the FISH aneuploidy screening and microarray testing in low-risk pregnancies.