With increasing cfDNA aneuploidy screening, there is a corresponding increase in “false positive” and “non-reportable” results in the setting of maternal malignancy. We hypothesize that these cfDNA results may be further characterized depending on stage and type of cancer. This was a retrospective review of cases with aneuploidy screening and a diagnosis of malignancy during pregnancy. We abstracted maternal history, diagnoses, screening results, and fetal outcomes from the medical record. We identified 13 cases from 2015-2019 with a malignancy in pregnancy. Four patients did not pursue aneuploidy screening. Three underwent first trimester screening and one underwent quad screening (all normal). Five patients had cfDNA screening (Table 1), three of whom had an abnormal result: a case of stage III rectal adenocarcionoma resulted “non-reportable”, a case of stage IV serous ovarian carcinoma resulted as “monosomy 13”, and a case of acute myeloid leukemia resulted as “concerning for maternal mosaic monosomy X”. There were two cases of non-metastatic breast cancer both of whom had normal cfDNA results. No fetuses had a genetic abnormality. Corroborating previous isolated case reports, we demonstrated “false positive” and “non-reportable” results on cfDNA screening secondary to maternal malignancy. Our data suggest that cancers with hematologic spread are likely to be detected by cfDNA, while those with less tumor shedding are not. Ultimately, cfDNA may prove useful in identifying certain types of malignancy. Conversely, fetal aneuploidy screening by cfDNA is not indicated in the case of known maternal malignancy as it may invalidate interpretation of fetal status. Larger patient cohorts are needed to further characterize the association of different tumor types and the pattern of cfDNA results, as well as to implement appropriate protocols for maternal diagnostic work up.