ABSTRACT
The aim of sperm preparation for assisted reproductive techniques (ARTs) is to maximize the chances of fertilization to provide as many normally fertilized oocytes as possible for transfer to the uterus or cryopreservation (1). With normal semen it is easy to obtain motile sperm by a variety of techniques. Abnormal semen, which will not yield adequate sperm for standard in vitro fertilization (IVF), needs to be recognized so that intracytoplasmic sperm injection (ICSI) can be used. Refi nements of the preparation procedures are required to obtain spermatozoa or elongated spermatids with the highest potential for normal fertilization from grossly abnormal semen samples or from samples obtained directly from the male genital tract. Sperm characteristics important for fertilization with standard IVF include normal morphology, normal intact acrosomes, straight line velocity (VSL) and linearity (LIN) and ability to bind to the zona pellucida, penetrate the zona pellucida, fuse with the oolemma, activate the oocyte, and form a male pronucleus (1). For ICSI, live sperm with an ability to activate the oocyte and form a pronucleus are necessary but morphology, motility, and acrosome status are generally not important (1-5). It is probably important to remove seminal plasma as it contains decapacitation factors and extraneous cells and degenerating sperm that may produce agents capable of damaging the sperm (6-8). For IVF or gamete intrafallopian transfer (GIFT), the medium should contain protein and buffers which promote sperm capacitation (1). While serum or high molecular weight fractions from serum appear to be important for sperm motility, more recently relatively pure preparations of human serum albumin, pasteurized to reduce the risk of transmitting infections, have been found to be adequate for sperm preparation for standard IVF and ICSI (9,10). Purifi ed and appropriately tested human serum albumin preparations are now routinely available from the major IVF media suppliers. The inclusion of protein in the culture medium is required to prevent sperm from adhering to surfaces. Although the concentration of albumin in human periovulatory oviductal fl uid is reported to be of the order of 30 mg/mL, concentrations of around 4 mg/mL will support normal sperm function in IVF. Bicarbonate ions are required for capacitation of sperm
and are normally present at a concentration of about 25mmol/L in the medium. Although glucose is utilized as a metabolic substrate by sperm it is not clear whether it is essential for normal function in vitro. It has been suggested that more recent media formulations, which do not contain glucose, may not be appropriate for fertilization stages of ART procedures.
