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BACKGROUNDIn natural conception only a few sperm cells reach the ampulla or the site of fertilization. This population is a selected group of cells since only motile cells can pass through cervical mucus and gain initial entry into the female reproductive tract. In animals, some studies indicate that the sperm selected by the reproductive tract and recovered from the uterus and the oviducts have higher fertilization rates but this is not a universal finding. Some species show less discrimination in sperm selection and abnormal sperm do arrive at the oviduct. In contrast, assisted reproductive technologies (ART) utilize a more random sperm population. In this review we contrast the journey of the spermatozoon in vivo and in vitro and discuss this in the context of developing new sperm preparation and selection techniques for ART.METHODSA review of the literature examining characteristics of the spermatozoa selected in vivo is compared with recent developments in in vitro selection and preparation methods. Contrasts and similarities are presented.RESULTS AND CONCLUSIONSNew technologies are being developed to aid in the diagnosis, preparation and selection of spermatozoa in ART. To date progress has been frustrating and these methods have provided variable benefits in improving outcomes after ART. It is more likely that examining the mechanisms enforced by nature will provide valuable information in regard to sperm selection and preparation techniques in vitro. Identifying the properties of those spermatozoa which do reach the oviduct will also be important for the development of more effective tests of semen quality. In this review we examine the value of sperm selection to see how much guidance for ART can be gleaned from the natural selection processes in vivo.

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The use of in-vitro fertilization (IVF) as a therapeutic tool in patients with endometriosis has provided information about the disease and, in particular, aspects of the reproductive process in humans, particularly folliculogenesis, fertilization, embryo development and implantation. Retrospective analyses of IVF and oocyte donation programmes showed impaired implantation in patients with endometriosis. Otherwise, the observation that embryo development was blocked more frequently in cases of endometriosis, suggested that impaired embryo quality may be responsible for the reduced implantation rates. Similarly, women with the disease undergoing oocyte donation had the same chance of implantation as patients without endometriosis, suggesting that the endometrial milieu is not affected in patients with endometriosis. The quality of the oocyte may, therefore, be altered in patients with endometriosis. To investigate this, we studied steroid secretion in women undergoing IVF. Progesterone concentrations in follicular fluid increased with the severity of the disease and an increase in progesterone accumulation in vitro was observed in basal and human chorionic gonadotrophin (HCG)-induced granulosa cell cultures. We postulated that the pattern of progesterone secretion may be related to the release of cytokines by ovarian and/or immune cells. To test this, we measured interleukin (IL)-1, IL-6 and vascular endothelial growth factor (VEGF) concentrations in serum, follicular fluid and granulosa cell cultures. IL-6 concentrations in serum were increased in natural cycles in women with endometriosis and showed a significant decrease in stimulated cycles in IVF. Also, IL-6 concentrations were increased in the follicular fluid of women with endometriosis and released in higher amounts by granulosa-luteal cells from patients with endometriosis. VEGF was accumulated in lower concentrations in the follicular fluid of endometriosis patients. These observations show that the follicular environment is different in cases with endometriosis and suggest that infertility in patients with endometriosis may be related to alterations within the oocyte which, in turn, result in embryos of lower quality, and with a reduced ability to implant.

Thus we concluded that time-lapse monitoring in the EmbryoScope does not impair embryo quality while allowing for morphological, spatial and temporal analysis of embryo development.

PL does not appear to have a negative impact on ongoing PR in our oocyte-donation programme.

Tena-Sempere M. KiSS-1 in the mammalian ovary: distribution of kisspeptin in human and marmoset and alterations in KiSS-1 mRNA levels in a rat model of ovulatory dysfunction. Am J Physiol Endocrinol Metab 296: E520 -

In spite of a great deal of effort over many decades, the mechanisms that lead to infertility in women with endometriosis remain unknown. Moreover, controversial results in the literature add even more difficulties in the understanding of this issue. Since the introduction of IVF, we have had the opportunity to study the effects of endometriosis at specific stages of the reproductive process including folliculogenesis, fertilization, embryo development and implantation. Depending on the research group, there are conflicting data on the results of IVF in patients with endometriosis. Some researchers found impaired implantation in patients with endometriosis, but such a defect in implantation may be caused by either defective embryos or altered endometrium. The observation of a higher rate of arrested embryos in patients with endometriosis compared with disease-free women, and that women with this pathological situation undergoing ovum donation had the same chance of implantation as patients without endometriosis, initially suggested that impaired oocyte/embryo quality may be responsible for reduced implantation. Further investigations on follicular components have also found differences between women with endometriosis and those without the disease. In addition, recent advances on implantation research, mainly on markers of endometrial receptivity, also show features in the eutopic endometrium of women with endometriosis that are not found in endometrium of women without the disease, although there is no agreement on this point. In this review, we will focus on infertility-related endometriosis based on our own research and the available literature.