Human Reproduction vol.13 no.4 pp.1003–1013, 1998 The successful use of pronuclear embryo transfers the day following oocyte retrieval*

A retrospective analysis of results from 114 initiated in-vitro fertilization cycles utilizing pronuclear embryo transfer is presented. Patients were unselected for age or infertility criteria, constituted a continuous series and were grouped according to response to stimulation (Group 1, ideal; Group 2, suboptimal) or ovarian reserve (Group 3, poor). At 16– 18 h post-insemination, embryos were scored for alignment of pronuclei and nucleoli and the appearance of the cyto-plasm, generating an embryo score (ES). Transfers were performed 24–26 h post-insemination using two to six embryos with the highest ES. A corrected score was calculated (total score/number of embryos; CS). A total of 114 initiated cycles resulted in 97 oocyte retrievals with 38 clinical pregnancies (39%; 15 % implantation). Pregnancy rates were significantly different between the three groups; 37 pregnancies in Group 1 (55 % clinical pregnancy; 20