OBJECTIVE: To estimate the accuracy and potential clinical effect of using massively parallel sequencing of maternal plasma DNA to detect fetal aneuploidy in a cohort of pregnant women carrying fetuses with nuchal cystic hygroma. METHODS: The Mat Ernal BLood IS Source to Accurately diagnose fetal aneuploidy (MELISSA) study database was queried to identify eligible patients carrying fetuses with cystic hygroma (n 5 113) based on clinical ultrasonographic examination reports near enrollment. Archived plasma samples were newly sequenced and normalized chromosome values were determined. Aneuploidy classifications for chromosomes 21, 18, 13, and X were made using the massively parallel sequencing data by laboratory personnel blinded to fetal karyotype and compared for analysis. RESULTS: Sixty-nine of 113 (61%) patients had fetuses with abnormal karyotypes, including trisomy 21 (n530), monosomy X (n521), trisomy 18 (n510), trisomy 13 (n54), and other (n54). There were 44 euploid cases; none was called positive for aneuploidy. The massively parallel sequencing detection rates were as follows: T21: 30 of 30, T18: 10 of 10, T13: three of four, and monosomy X: 20 of 21, including two complex mosaic cases. Overall, using massively parallel sequencing results of the four studied chromosomes, 107 of 113 (95%, 95% confidence interval [CI] 88.8-98.0) cases were accurately called by massively parallel sequencing, including 63 of 65 (97%, 95% CI 89.3-99.6) of cases of whole chromosome aneuploidy. CONCLUSION: Massively parallel sequencing provides an accurate way of detecting the most prevalent aneuploidies associated with cystic hygroma. Massively parallel sequencing could advance prenatal care by providing alternative point-of-care noninvasive testing for pregnant women who either decline or do not have access to an invasive procedure.