Who benefits from putting family life into ice?

The first methods for fertility preservation (FP) were sperm freezing followed many years later by ovarian tissue freezing and oocyte vitrification. FP before cancer treatment is necessary because gametes are often destroyed at the same time as the cancer therapy kills malignant cells. It has been regularly offered to male cancer patients in the form of sperm cryopreservation. In female patients, slow freezing of ovarian tissue containing the oocytes was initiated in 1996 (1). It has since then been used for hundreds of young women, and after re-transplantation of the tissue back to the woman’s ovary after her cancer treatment tens of healthy children have been born (2). There are also genetic disorders in which FP is needed, such as Turner syndrome (3). Ovarian tissue has to be biopsied under general anaesthesia. But getting mature oocytes instead of tissue is a simpler procedure. Oocytes are picked up using trans-vaginal ultrasound-guided needle aspiration after the woman’s hormonal stimulation, which is routine procedure for in vitro fertilization (IVF). Ovarian tissue freezing is the only method available for prepubertal girls, but it is not needed for age-related decrease in fertility. Human sperm has been frozen for about 60 years with the aim to use it later on for having children. Spermatozoa are very small cells, and it was technically relatively easy to cryostore them. But human eggs, oocytes, are very large cells. The diameter of a mature human egg is 120 lm. They are extremely sensitive to damage during freezing. But cryostorage of human eggs has also become feasible. The first attempts, using the conventional slow freezing method with dimethylsulphoxide as the cryoprotectant, were successful already 30 years ago and resulted in pregnancies and births (4,5), but the efficacy was low. The main cause of damage in slow freezing of cells is that ice crystals break intracellular organelles and cellular membranes. Vitrification is a cryostoring method in which low temperatures are achieved by adding high concentrations of cryoprotecting substances that form a glass-like amorphous mass when cooled to subzero temperatures. Hence, dangerous sharp ice crystals are avoided. The cooling rate has to be fast in order to avoid the toxicity of the cryoprotectants. Vitrification of human oocytes then evolved (6). It proved soon more successful than slow freezing (7–11). The feasibility was shown in large oocyte donation programmes. Today, vitrification of oocytes is the most favoured method of fertility preservation. Hence, it is easy to understand that it is also offered to women who want to postpone their childbirths to higher age than is physiologically feasible. It is called egg freezing for non-medical reasons, or social egg freezing. Egg freezing for non-medical reasons, with the indication to postpone childbirths, is today offered by several private IVF units for women who are willing to buy these treatments. In the USA, big companies, such as Google and Facebook, are offering it for their employees.