ABSTRACT
BACKGROUND e use of assisted reproduction technology (ART) to overcome infertility has increased steadily in the U.S.A. and worldwide (1). Based on 2012 estimates, approximately 456 ART clinics in the U.S.A. performed 157,635 ART procedures resulting in 51,261 live deliveries and 65,151 infants (1). In 2012, ART contributed to 1.5% of all infants born in the U.S.A. (1). ART generally includes treatments such as in vitro fertilization (IVF), gamete intrafallopian transfer and zygote intrafallopian transfer, with IVF accounting for approximately 99% of all ART procedures (1). Soon aer the establishment of IVF, it became clear that as many as 40% of conventional IVF cycles were aected by fertilization failure or by an extremely low fertilization rate, even though spermatozoa were placed in close proximity to oocytes (2). is was particularly problematic in patients with diminished sperm motility and/or poor morphology (i.e., it presented a complex obstacle for spermatozoa to penetrate the zona pellucida [ZP], a thick glycoprotein layer surrounding the oocyte) (2). In such cases, gamete micromanipulation was thought to be the only way to overcome this problem. e dierent techniques developed in this regard focused on assisting the spermatozoon to penetrate the ZP by “soening” it enzymatically with trypsin or pronase, or penetrating it chemically via localized or “pinpoint” exposure to acidied Tyrode’s solution prior to sperm exposure (3). e placing of the spermatozoon beneath the ZP yielded consistent results, achieving a fertilization rate of ∼20% (4). However, these techniques were abandoned because of limiting factors such as the need for many functional spermatozoa with good progressive motility, and complications like polyspermy (5). ese initial eorts to assist sperm penetration soon became obsolete with the introduction of a microsurgical method for insertion of spermatozoa directly into the oocyte.
