Sperm selection in natural conception: what can we learn from Mother Nature to improve assisted reproduction outcomes?

Abstract

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.

Storm Power, an Icy Tower and Elsa’s Bower: The Winds of Change in Disney’s Frozen

“…As such, it is strictly socially mandated that all wedding guests drink following a toast. An empty glass or refusal to join in the toast is taboo; all guests must imbibe fluid that is dedicated to the hydration and thus fertility of the couple (Sakkas et al 2015) traditionally mandated to be fruitful and multiply. Wine (or sparkling wine) is the drink of choice, which is likely because Dionysus, the god of wine who was born from Zeus' thigh, promotes fertility.…”

Improving the safety of the embryo and the patient during in vitro fertilization procedures

“…The clinical diagnostic value for HA binding theoretically attempts to mimic which sperm will bind to the cumulus cells. As sperm binding to the cumulus–oocyte complex is one of the final steps in natural selection, the utility of this test would appear to be promising; however, larger studies are urgently needed [16]. …”

MACS (<i>Magnetic Activated Cell Sorting</i>) antes ou após a centrifugação em gradiente de densidade para o preparo seminal

“…This shows that performing MACS after a classical sperm separation technique is an unsuitable protocol (Cakar et al, 2016), in agreement with our findings. As progressive motility is essential feature for the success of certain ARTs, such as intrauterine insemination (IUI) and in vitro fertilization (IVF) Berker et al, 2012;Sakkas et al, 2015), it is fundamental to evaluate this parameter. Our study is the first to demonstrate that the MACS performed before DGC yields a significantly higher percentage of progressive sperm than the DGC-MACS procedure (68% vs. 10%), simultaneously assessing the motility and concentration of spermatozoa in the same protocol.…”

“…(Said et al, 2005;Aziz et al, 2007) showed no improvement in the percentage of cells with normal morphology following MACS, but reported a decrease in this variable in normozoospermic patients (Delbes et al, 2013). However, the impact of sperm morphology in natural fertility and the success of ART remains poorly elucidated (Nikbakht and Saharkhiz, 2011;Sakkas et al, 2015).…”

“…Na atualidade o impacto da morfologia espermática na fertilidade natural e sucesso das TRA permanece pouco elucidado (Nikbakht e Saharkhiz, 2011;Sakkas et al, 2015), de modo que não é possível inferir se a recuperação de maior percentagem de espermatozoides com morfologia normal poderia impactar positivamente os resultados das TRA.…”