Cryopreservation of ovarian tissue followed by auto-transplantation is a promising method for fertility preservation in girls and young women at risk of premature ovarian insufficency as a result of anti-cancer treatment when ovarian stimulation is not possible [
1,
2]. Cryopreservation of ovarian tissue can be performed by slow-freezing or vitrification. Slow-freezing has resulted in 37 live births worldwide after orthotopic transplantation [
3,
4]. However, two major issues with slow-cooling protocols are that they are time-consuming and often require costly equipment. We recently addressed the first issue by developing a serum-free 1,2-propanediol (PrOH), raffinose-based solution supplemented with antioxidants that gave promising results in terms ovarian integrity and functionality, even when used in combination with a faster cooling program than the usual one [
5,
6]. Over the last decade, numerous studies have investigated vitrification as an alternative to conventional slow-freezing for ovarian tissue [
7], and different vitrification solutions and methods, mostly adapted from blastocyst and oocyte vitrification, have been applied. Live offspring have been born from vitrified mouse ovarian preantral follicles matured
in vitro, and orthotopic autografting of vitrified/warmed sheep hemi-ovaries has led to the birth of four lambs [
8‐
10]. In humans, two live births were recently reported after ovarian tissue vitrification followed by
in vitro activation of dormant follicles in patients with primary ovarian insufficiency [
11]. The issue of whether vitrification is superior to slow-freezing for cryopreserving human ovarian tissue remains unresolved. Rahimi
et al. observed a higher percentage of apoptotic cells in vitrified human ovarian tissues after grafting compared to slow-frozen tissues [
12], and Oktem
et al. showed higher primordial follicle density and viability after slow-freezing compared to vitrification [
13]. However, other studies have failed to find any difference between these two cryopreservation procedures in terms of the proportion of morphologically intact follicles and proportion of apoptotic cells [
14,
15]. These discrepant conclusions likely reflect either heterogeneity in the cryopreservation protocols applied, which ovarian components may be particularly sensitive to, and/or disparities in the methods employed to evaluate ovarian tissue quality. Limited access to donated ovarian tissue places limits to comparative studies between vitrification and slow-freezing methods, and few studies have compared the effects of these two methods on ovarian tissue from the same patient. Here we investigated follicle integrity following vitrification with a novel PrOH, ethylene glycol (EG) and raffinose-based procedure. The efficiency of this vitrification procedure was evaluated by carrying out a systematic comparison with our earlier PrOH and raffinose-based slow-freezing protocol.