Fertility preservation in men and women: Where are we in 2021? Are we rising to the challenge?

Demand for fertility preservation in women for oncologic, nononcologic, and personal reasons has increased dramatically. Meeting that demand is a major challenge, and we are rising to the challenge. Mature oocyte cryopreservation after ovarian stimulation and ovarian tissue cryopreservation are both methods endorsed by the American Society for Reproductive Medicine (formerly The American Fertility Society), and numerous papers confirmed their efficacy. In girls and women with leukemia or cancers who are at a high risk of ovarian metastasis and who may not be eligible for ovarian tissue transplantation, restoration of fertility can only be achieved by in vitro methods. Male fertility preservation has also become a pressing issue and is extensively reviewed in the present journal issue.

History of cryobiology, with special emphasis in evolution of mouse sperm cryopreservation.

Confucius said study the past if you would define the future and a popular statement says that history depends on who writes it. To talk about history it is necessary to find and define a milestone where to start the narration. The intention of this quick review is to take the reader through moments and selected publications; part and pieces of memories showing how the concept of cryopreservation, specifically for mouse sperm, was conceived and sustained as we know it today. Beginning with the development of the microscope (1677) and continuing through the 17th century with the first documented observation by L. Spallanzani describing that sperm could maintain the motility under cold conditions. As J. Sherman suggested, we divide the cryopreservation evolution into two sequences, previous to and after 1949 when Polge, Smith and Parkes discovered the property of glycerol as cryoprotectant. Later, in 1972, D. Whittingham, S. Leibo, and P. Mazur applying a slow freezing process achieved the first embryo freezing (mouse). During that time many theories were scientifically confirmed. Among those, Peter Mazur demonstrated the relation between the speed of freezing and intracellular ice formation, and Stanley Leibo that each cell type has their unique freezing curve. In 1950, after the discovery of the protective aspect of glycerol, sperm from many mammals were frozen, except from the mouse. It was in the early 90's when the mouse sperm freezing becomes important and it was a real challenge for many groups, nevertheless, the technique using skim milk and raffinose modified by Dr Nakagata was the beginning of a different story ….

French field results (1985-2005) on factors affecting fertility of frozen stallion semen.

Results on procedures for freezing stallion semen and the subsequent fertility during 20 years are presented. The present system applied in French National Stud includes: (1) a freezing protocol (dilution in milk, centrifugation and addition of freezing extender (INRA82+egg yolk (2%, v/v)+glycerol (2.5%, v/v) at 22 degrees C, a moderate cooling rate to 4 degrees C and freezing at -60 degrees C/min in 0.5-ml straws); (2) selection of ejaculates showing post-thaw rapid motility >35%; and (3) an insemination protocol (mares examined once daily, two AI of 400 x 10(6) spermatozoa 24 h apart before ovulation, sufficient number of straws to have the possibility to perform six AI of 400 x 10(6) total spermatozoa, i.e. 2.4 x 10(9) total spermatozoa available per mare per season). This system was applied to >110 stallions per year, the average post-thaw motility of ejaculates was 50% (>1800 ejaculates) before selection. The semen freezability was defined as the number of selected ejaculates divided by the total number of ejaculates frozen. Of the stallions, 5, 4, 5, 21 and 64% had semen freezability of 0-10, 10-33, 33-60, 60-90 and over 90%, respectively. Per-cycle pregnancy rate was 45-48% (>1500 mares per year, 1.8 cycles per mare) and foaling rate 64%. In comparison, per-cycle pregnancy rate and foaling rate of mares hand-mated to stallions were 57-59% and 64%, respectively. The average number of straws used was 32-35 (1.75 x 10(9) total spermatozoa) per mare per season. According to our results and the literature, the most important factors for improving fertility of frozen equine semen include: (1) a low concentration of glycerol (2-3.5% final concentration); (2) a suitable base extender for freezing like Lactose-Glucose EDTA or INRA82; (3) a post-thaw motility >30-35%; and (4) a sufficient number of spermatozoa per mare per season (1.5-2 x 10(9) total spermatozoa for two to three cycles) divided into small units. Numbers of spermatozoa, lower than 750.10(6) total spermatozoa per cycle, could result in lower per-cycle pregnancy rate with higher additional costs for management of mares. Because there are no particular regulations on quality and quantity of equine semen in the European Community, there is a need for the uniformity of information about frozen semen. A codification is suggested, based on the number of spermatozoa available per mare per season, the post-thaw motility and the final glycerol concentration.

Dynamism to promote reproductive medicine and its development, Rihachi Iizuka.

Rihachi Iizuka has contributed strong leadership for the remarkable development of reproductive medicine which has undergone a complete transformation in the previous half century. The Keio University Hospital introduced artificial insemination as the first assisted reproductive technology in Japan. As it follows, lizuka and his colleagues first reported the live birth of a female infant in August 1949 after heterologous insemination: AID. Iizuka and his colleagues were also among the first to successfully inseminate a woman with sperm that had been frozen. He developed the new cryopreservation medium for human semen called "KS Cryo-medium". He also developed semen preparation methods of washing and concentrating sperm counts by centrifugation with Percoll (colloidal silica derivative) solution for oligozoospermic patients. These methods are broadly used in the clinical field. Furthermore, he developed the X-, Y-bearing sperm preseparation method using Percoll which is the so-called "gender selection" procedure for preventing X-linked genetic disorders. The most striking assisted reproductive technology was in vitro fertilization first carried out in Britain. Prior to the clinical application in Japan, the Japan Society of Fertilization and Implantation was established as the main organ for the exchange of official scientific information by lizuka in 1982. As rapid development and spreading of in vitro fertilization and its implicated technologies, lizuka and his colleague of the department had the first success of offspring following embryo freezing and thawing in Japan which was performed at the Tokyo Dental College Ichikawa General Hospital. Already the numbers of offspring following in vitro fertilization treatment has risen to approximately 1% of births in Japan. Rihachi lizuka still undertakes the responsibility for reproductive medicine as he has done so far.