Current Trends in Clinical Embriology 2015; 2 (2): 73-80 73 Mini-review Sperm selection before intracytoplasmic sperm injection Riccardo Talevi Roberto Gualtieri Department of Biology, University of Naples "Fe- derico II", Complesso di Monte S. Angelo, Napoli, Italy Address for correspondence: Riccardo Talevi, MD, PhD Department of Biology University of Naples “Federico II” Complesso Universitario Monte S. Angelo Via Cinthia - 80126 Napoli, Italy Phone: +39 081 679198/197 E-mail: riccardo.talevi@unina.it Summary In assisted reproduction techniques (ART), the success of embryo development depends mostly on the quality of gametes, and pregnancy outcome is strictly related to both the oocyte and the fertil- izing sperm quality. Therefore, during ART, it is mandatory to select a mature and viable sperm with high DNA integrity. Routine sperm prepara- tion and selection in ART is based on density gra- dient centrifugation or motility. However, it is be- coming increasingly clear that new and more rig- orous procedures should be considered to recover those sperm able to properly support fertilization, embryo development and birth of healthy babies. KEY WORDS: ICSI, sperm selection, DNA fragmen- tation. Introduction In natural conception the millions of sperm ejaculated at coitus, undergo a progressive physiological selection during their journey within the female reproductive tract. During their competitive race to reach and fertil- ize the oocyte in the ampulla, sperm interact with sev- eral biological checkpoints that allow the passage of competent sperm. After the interaction with the cervi- cal mucus, the utero-tubal junction (UTJ) and the oviduct epithelium only 10 2 -10 3 sperm endowed with high fertilization competence arrive at the ampulla (1). In assisted reproduction techniques (ART), the success of embryo development depends mostly on the quality of gametes, and pregnancy outcome is strictly related to both the oocyte and the fertilizing sperm quality (2). Therefore, during ART, it is mandatory to select a mature and viable sperm with high DNA in- tegrity. Although, sperm selection has been one of the primary focal points during the development of in vitro fertilization techniques, the possibility to non in- vasively identify sperm endowed with these features is still an unsolved problem. Nowadays, sperm prepara- tion and selection in ART is based on density gradient centrifugation or motility and allows the recovery of fractions enriched with sperm with normal morphol- ogy and/or forward progressive motility for use in both in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). Motile normomorphic sperm, recovered from routine sperm selection methods, are then visually selected at 200-400 x magnification by gross morphological parameters for insemination dur- ing ICSI. However, it has been reported that in severe male infertility the percentage of normomorphic sperm showing DNA fragmentation is increased (3). Al- though, such methods are those routinely used for in vitro sperm selection, it is becoming increasingly clear that new and more rigorous procedures should be con- sidered to recover those sperm capable of supporting proper fertilization, embryo development and birth of healthy babies. This paper is intended to update the main sperm separation methods currently used in ART, in the light of new insights into the physiological mechanisms of in vivo and in vitro sperm selection in the human and in animal models. Sperm selection within the female reproductive tract Natural sperm selection checkpoints during the sperm journey within the female tract are represent- ed by cervical mucus, utero-tubal junction (UTJ), oviductal isthmus, oocyte cumulus oophorus and zona pellucida (ZP). Each of them acts sequentially and has been demonstrated to select higher quality sperm subpopulations. © CIC Edizioni Internazionali