Risk of contamination of germplasm during cryopreservation and cryobanking in IVF units

Abstract

Cryopreservation of sperm, embryos and, more recently, oocytes plays an important and increasing role in assisted reproduction, due to improvements of old, and introduction of new technologies. In parallel, concerns are increasing about the technical and biological safety of these procedures. However, published data regarding the confirmed or theoretical hazards of these procedures are sparse and sometimes contradictory. The purpose of this review will summarize data and opinions about one of the most disputed risks, the potential hazard of contamination and disease transmission through cryopreservation. Special attention is concentrated on the weak points of the technology including open vitrification systems, sterilization of liquid nitrogen and safety of commonly used storage tanks including straws and cryovials. Suggestions are also made for practical measures to avoid these dangers while preserving the benefits and perspectives of new cryopreservation technologies.

Neonatal outcomes after the implantation of human embryos vitrified using a closed-system device

“…The data obtained from single embryo transfer is of great value for assessing the effects of closed vitrification. There are two steps that could cause contamination during the vitrification procedure [13,14]. The first occurs during the rapid cooling procedure via direct contact with liquid nitrogen.…”

“…The contaminated liquid nitrogen would then cause cross-contamination. Since an embryo is vitrified in supercooled air in a closed device and then packaged in a closed straw [19], the risk of contamination from liquid nitrogen could be decreased as compared with that in an open device [13,14,33], in a manner similar to that of conventional freezing [33] and packaged straw vitrification [34].…”

“…This idea was initially proposed for freezing Drosophila embryos [6], and drastic improvement in viability has since been shown in both animal studies [7][8][9][10] and clinical reports [11,12]. However, there are some potential drawbacks of the open vitrification system, such as the sterility of liquid nitrogen and the risk of cross-contamination during long-term storage [13,14]. Such cross-contamination could arise from direct contact of the solution containing the oocytes and embryos with the liquid nitrogen.…”

A closed system supports the developmental competence of human embryos after vitrification

“…As a result, the embryo is supposed to have low risk of contamination from liquid nitrogen [16] similar to conventional slow freezing [7] and packaged-straw vitrification [34]. However, this contrasts to direct contact with open vitrification [3].…”

“…Animal data [11,15,22,31] and recent analyses of clinical reports [18,19] have revealed the benefits of vitrification such as low rates of cellular damage. However, the transition from freezing to vitrification is proceeding very slowly due to concerns regarding the sterility of liquid nitrogen and the risk of cross-contamination during long-term storage [2,3]. These concerns arise from direct contact of the solution containing the oocytes/embryos with liquid nitrogen.…”