INTRODUCTION: Two types of cell free DNA (cfDNA) platforms are available to screen for fetal chromosome abnormalities. The “limited” platform screens for a fixed number of chromosomal abnormalities while the “expanded” platform screens for abnormalities throughout the entire genome. We sought to compare the accuracy of these two platforms. METHODS: We performed a retrospective review of pregnancies undergoing cfDNA, invasive genetic testing, or both, between 2015-2016. Singleton high risk pregnancies were included. Maternal and newborn charts were reviewed to determine which cfDNA platform was performed and whether prenatal or postnatal genetic testing was performed. Appropriate statistical tests were performed for parametric and non-parametric data. Significant chromosome abnormalities were defined as whole chromosome aneuploidy, subchromosomal abnormalities >7 megabases and 22q deletion. RESULTS: 790 cfDNA assays were performed: 384 limited, 406 expanded. 44 chromosomal abnormalities were found (34 prenatally, 10 postnatally). 75% were common trisomies or sex chromosome aneuploidies while 25% were uncommon chromosomal abnormalities (deletions, duplications, unbalanced translocations, triploidy, rare autosomal trisomy). The expanded platform could potentially have detected 94% of the total number of abnormalities while the limited platform could potentially have detected only 75% (p=.03). CONCLUSION: We found that that 25% of chromosomal abnormalities in a high risk population cannot be detected by a limited cfDNA platform. Clinicians should consider usage of an expanded genome wide cfDNA platform that screens for pathogenic, clinically relevant, actionable chromosome abnormalities in patients who prefer non-invasive screening as first line testing.