Objectives: Embryo selection is an important contributor to success after IVF. A number of studies have identified correlations between early embryo morphology, chromosomal integrity, and developmental competence. Our goal was to extend those studies to blastocysts.Design: This is a prospective study to determine which chromosomal abnormalities in cleavage stage embryos are compatible with development to the blastocyst stage and which are selected against in extended culture.Materials and Methods: Embryos used for this project were donated for research in accordance with guidelines approved by our Internal Review Board, including informed written consent in each case. Embryos were obtained from 27 patients (29 cycles) undergoing preimplantation genetic diagnosis (PGD) for aneuploidy using FISH with probes for chromosomes X, Y, 1, 13, 15, 16, 18, 21 and 22. A total of 179 embryos were diagnosed as chromosomally abnormal or were unsuitable for embryo replacement (male embryos with X-linked disease or embryos with no FISH result during PGD). After blastomere biopsy on day 3, embryos were cultured in microdrops of G2 medium and their development was monitored daily until day 5. Arrested embryos were fixed using Tarkowsky’s method (1966); blastocyst fixation was according to the protocol of Clouston et al. (1997). All embryos were analyzed by two rounds of FISH with the same probes used in the original PGD analysis.Results: Of the 179 embryos cultured to day five, 48 were classified as blastocysts. The morphology of those embryos was optimal in six, sub-optimal in 19, and abnormal in 19; four embryos were not classified. The following table shows the chromosome abnormalities developing to blastocyst. If blastocyst with abnormal morphology were not transferred, 52% of the abnormalities arriving to blastocyst detected would be eliminated. Tabled 1Mono- somicTrisomicHaploid>40% mosaic<40% mosaicNormalDay 333384612513Blastocyst3∗1109166(∗two monosomies 21, one monosomy X) Open table in a new tab Discussion: By extending in vitro culture period to five days, embryos with haploidy and autosomal monosomy (with the exception of monosomy 21) are eliminated as these anomalies lead to early embryonic arrest. However, other abnormalities such as extensive (>40%) mosaicism, trisomy and polyploidy cannot be completely screened out by extended culture. The only option for exclusion of such embryos from transfer is PGD. Objectives: Embryo selection is an important contributor to success after IVF. A number of studies have identified correlations between early embryo morphology, chromosomal integrity, and developmental competence. Our goal was to extend those studies to blastocysts. Design: This is a prospective study to determine which chromosomal abnormalities in cleavage stage embryos are compatible with development to the blastocyst stage and which are selected against in extended culture. Materials and Methods: Embryos used for this project were donated for research in accordance with guidelines approved by our Internal Review Board, including informed written consent in each case. Embryos were obtained from 27 patients (29 cycles) undergoing preimplantation genetic diagnosis (PGD) for aneuploidy using FISH with probes for chromosomes X, Y, 1, 13, 15, 16, 18, 21 and 22. A total of 179 embryos were diagnosed as chromosomally abnormal or were unsuitable for embryo replacement (male embryos with X-linked disease or embryos with no FISH result during PGD). After blastomere biopsy on day 3, embryos were cultured in microdrops of G2 medium and their development was monitored daily until day 5. Arrested embryos were fixed using Tarkowsky’s method (1966); blastocyst fixation was according to the protocol of Clouston et al. (1997). All embryos were analyzed by two rounds of FISH with the same probes used in the original PGD analysis. Results: Of the 179 embryos cultured to day five, 48 were classified as blastocysts. The morphology of those embryos was optimal in six, sub-optimal in 19, and abnormal in 19; four embryos were not classified. The following table shows the chromosome abnormalities developing to blastocyst. If blastocyst with abnormal morphology were not transferred, 52% of the abnormalities arriving to blastocyst detected would be eliminated. Tabled 1Mono- somicTrisomicHaploid>40% mosaic<40% mosaicNormalDay 333384612513Blastocyst3∗1109166(∗two monosomies 21, one monosomy X) Open table in a new tab Discussion: By extending in vitro culture period to five days, embryos with haploidy and autosomal monosomy (with the exception of monosomy 21) are eliminated as these anomalies lead to early embryonic arrest. However, other abnormalities such as extensive (>40%) mosaicism, trisomy and polyploidy cannot be completely screened out by extended culture. The only option for exclusion of such embryos from transfer is PGD.