Your embryos can be tested for abnormal chromosomal numbers before they are transferred to the uterus. This is called preimplantation genetic screening. PGS may increase live birth rate and decrease miscarriage rate in certain patient population. Embryos will develop in the incubator until they reach blastocyst stage (typically after 5-7 days), then 5-7 cells from trophectoderm (placenta in the future) are removed and tested for chromosomal numbers. Embryos that have normal chromosomal numbers can be transferred back.