OBJECTIVE To evaluate independently the effect of blastomere number and degree of fragmentation on pregnancy outcome following single ETs in women with a decreased egg reserve. DESIGN Retrospective cohort analysis. SETTING In vitro fertilization center of a university-based practice. PATIENT(S) Women having a single ET related to a decreased egg reserve. A requirement for inclusion was a day 3 serum FSH >12 mIU/mL and < or =3 antral follicles on ultrasound. INTERVENTION(S) Patients received no or minimal stimulation with gonadotropins. MAIN OUTCOME MEASURE(S) Pregnancy rates (PRs) following single ETs were evaluated according to blastomere number (group 1, < or =4 cells; group 2, 5 cells; group 3, 6 cells; group 4, 7 cells; and group 5, > or =8 cells) and fragmentation index (A, no fragmentation; B, 1-25% fragmentation; and C, >25% fragmentation). Embryo transfers and morphologic evaluation were performed on day 3. RESULT(S) The clinical and delivered PRs according to blastomere number showed that 6-8-cell embryos were six times more likely to implant than 4-5-cell embryos (6.6% versus 40.4% clinical). Degree of fragmentation did not predict outcome nearly as well as blastomere number. The overall clinical and delivered PRs per transfer were 27.8% and 24.1%, respectively, and were 14.8% and 12.8% per retrieval, respectively, and were 9.0% and 7.3% per initiated cycle, respectively. CONCLUSION(S) Six, seven, or eight-cell embryos have equal chances of implanting in women with day 3 elevated serum FSH. The key finding is that these embryos do better than those with <6 blastomeres. These data may be helpful in women with a diminished ovarian reserve in attempting IVF with their own eggs or when choosing donor oocytes.