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The relative importance that endometrial development and embryo quality have on implantation rates achieved with assisted reproductive technology (ART) is the subject of controversy. Ovarian stimulation has been repeatedly mentioned as having a detrimental effect on endometrial receptivity (Paulson et al., 1990, Fertil. Steril., 53, 870-874). We compared pregnancy and implantation rates achieved with ART during stimulated cycles and hormonal replacement cycles, in patients matched for the following criteria: age < 35 years for the patient donating oocytes; transfer of at least two good quality embryos/oocytes and good quality transfer. All transfer cases performed during hormonal replacement cycles were done with donated oocytes. Comparison of results between techniques was not attempted due to potential differences in populations. The pregnancy and implantation rates achieved with each technique during stimulated and hormonal replacement cycles were not statistically different. In contradiction to previous results, our data suggest that differences in uterine receptivity between stimulated and hormonal replacement cycles in the age group studied are not of critical importance in embryo implantation. Good embryo quality appears to be the dominant factor in determining the success of ART.

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Microsurgical epididymal sperm aspiration (MESA) and in vitro fertilization (IVF) is primarily offered to men with congenital absence of the vas deferens (CAVD). However, the IVF capacity of these epididymal sperm is low ( < 15%) and unpredictable. In this study, IVF and intracytoplasmic sperm injection (ICSI) results in patients with non-congenital, irreparable obstructive azoospermia were analysed. Thirty-three patients were evaluated for a total of 37 cycles of MESA and IVF. Most had obstruction secondary to failed vasectomy reversal and to epididymal blockage. The overall fertilization rate was 30% with regular IVF and 26% with ICSI, and six clinical pregnancies were obtained. Both rates are significantly higher than the IVF rate previously reported with sperm from men with CAVD (13%, P < 0.00001). In men with non-congenital obstructive azoospermia, a significant difference was found in the average sperm count (56.9 x 10(6) v. 12.3 x 10(6), P < 0.04) and total motile count (16.6 x 10(6) v. 1.6 x 10(6), P < 0.01) respectively for patients who achieved IVF and those who did not. It is concluded that (a) the real IVF capacity of human epididymal sperm is 30%, or 42%, if calculated only for patients who achieved fertilization, (b) this higher rate is an indirect support of the hypothesis that sperm from men with CAVD have intrinsic biochemical defects, related to cystic fibrosis mutations, responsible for their low and unpredictable IVF rate, and (c) MESA and IVF can be offered at the same time or as an alternative to patients requesting vasectomy reversal.

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