Full autosomal monosomy embryos are lethal, so they don’t implant or result in early pregnancy loss. In cases where no euploid embryos are available, the transfer of monosomic embryos might be considered. The objective of this study was to report the results in which only monosomic embryos were transferred. Retrospective analysis of 13 frozen embryo transfers (FET) between January 2013 to April 2016 in which only full monosomic embryos were transferred. Multiple trophectoderm cells were biopsied on day 5/6 blastocysts and sent for preimplantation genetic screening (PGS) by array-comparative genomic hybridization (aCGH). Embryos were vitrified and used for subsequent FET. If no, or inadequate number of euploid embryos were present, the patient was offered the transfer of selected monosomic embryo(s) for FET. Patients were counseled of risk and signed an informed consent. From January 2013 to April 2016, 1076 FET-PGS cycles were performed. The transfer of monosomic embryos was made available for 13 women whom IVF had resulted in no euploid embryos. The clinical outcomes are reported in the table I.Tabled 1Table I. Clinical Outcomes of Monosomic Blastocysts TransferredPatient n°Karyotype of transferred embryosClinical outcome145, XX, -4Baby healthy at birth245, XY, -22No pregnancy345, XY, -1No pregnancy445, XX, -8; 45, XX, -21No pregnancy545, XY, -5No pregnancy645, XY, -5No pregnancy745, XX, -21; 45, XY, -22No pregnancy845, XX, -5No pregnancy945, XY, -22; 45, XY, -16No pregnancy1045, XX, -21No pregnancy1145, XX, -4No pregnancy1245, XY, -15No pregnancy1345, XY, -19No pregnancy Open table in a new tab A concern of PGS is ‘false positive’ embryos being discarded or ‘false negative’ embryos transferred. In our study an embryo that was diagnosed as full monosomy 4 was transferred resulting in a healthy live birth. A possible explanation for the misdiagnosis may be mosaicism, where different genetic cell lines are segregated in the trophectoderm of the embryo, while the inner cell mass contained only euploid cells. Sampling errors during biopsy and the lack of sensitivity necessary to detect minor cell populations makes mosaicism difficult to detect for aCGH, resulting in misdiagnosis. aCGH in PGS is still not fully definitive in the diagnosis of aneuplody. The patient must be approprietely counseled of risk, requirement of prenatal screening and possibility of termination of pregnancy before the transfer of full autosomal monosomic embryos.