- Objective : To compare ovarian response and pregnancy rate between women with one and two ovaries undergoing in vitro fertilization and embryo transfer (IVF/ET). Study design : 20 IVF/ET treatment cycles in ten women with a single ovary were compared with 60 IVF/ET cycles in 47 women with two ovaries. Both groups were matched for age and treated for mechanical infertility. In both groups treatment protocol included gonadotropin releasing hormone/human menopausal gonadotropin/human chorionic gonadotropin (GnRH/hMG/hCG). Results : Effective daily dose of gonadotropins (3.7±0.7 vs. 3.6 ±1.0), mean 17β-estradiol levels on day of hCG administration (1136±467 vs. 1343±776), number of retrieved oocytes (6.4± 3.7 vs. 8.3±4.2) and number of embryos per transfer (3.0±0.7 vs2.9±1.2) were not statistically different between the groups. A significantly higher pregnancy rate was observed among women with one ovary (52.9%) as compared with those with two ovaries (20.8%), ( P =0.015). Multivariate logistic regression analysis demonstrated an odds ratio of 5.73 for patients with a single ovary. Conclusion : Treatment outcome in patients with a single ovary undergoing IVF/ET is comparable to those with two ovaries. The unexpected significantly higher pregnancy rate observed among these patients need to be further evaluated.