Objective: To determine whether the embryonic chromosomal anomalies are responsible for early pregnancy loss in patients with PCOS.Design: Perspective cohort study.Setting: Hospital-based academic medical center.Patient (s) : Fifty miscarriages who conceived after a single cycle of controlled ovarian stimulation combined with intrauterine insemination (IUI) for mild male factors, or in vitro fertilization-embryo transfer (IVF-ET)for tubal factors.Amongst these subjects, 14 patients had PCOS and 36 patients did not have PCOS.All subjects included had ultrasound evidence of a gestational sac on the 55+4 gestational days (52 to 60 days).Biochemical pregnancy was excluded from the study.Intervention (s) : Abortus tissues were collected during uterine curettage.Genetic analysis were performed by the use of conventional cultured chorionic villous chromosome karyotyping and multiplex ligation-dependent probe amplification (MLPA) combined with fluorescence in situ hybridization (FISH).Result (s) : In PCOS group, 3 out of 14 (21.4%) abortus demonstrated aneuploidy, which was significantly lower than 23 out of 36 (63.9%) in the non-PCOS group.Conclusion (s) : In the early miscarriage, the risk of embryonic aneuploidy in women with PCOS is lower than that of women without PCOS.