Pregnancies and births after oocyte cryopreservation

Qualitative and morphometric analysis of the ultrastructure of human oocytes cryopreserved by two alternative slow cooling protocols

“…However if this assumption is correct, it remains to be explained why oocytes vitrified through the cryoleaf method, which are exposed to high concentrations of CPAs, do not exhibit an increase in the number of vacuoles, as we recently reported [39]. Regardless their origin, vacuoles may be adopted as a specific indicator of cryodamage and reduced developmental potential in cryopreserved oocytes, considering that an increased number of vacuoles [19] and a reduced developmental ability [14,15] is associated to certain CRSC protocols. Preliminary evidence suggest that vitrification protocols may be compatible with high implantation ability [7] and a normal occurrence of vacuoles [39].…”

“…Distribution, amount, shape and electron-density of these organelles were virtually indistinguishable between fresh and cryopreserved groups. Previously, we reported that mitochondria-SER associations were undisturbed in oocytes cryopreserved with CRSC protocols relying on PrOH as a intracellular CPA [19] and used in the clinical practice [14,15]. Conversely, other cryopreservation conditions may be in fact deleterious to mitochondria-SER aggregates.…”

“…In fact, after approximately 20 years of efforts in basic and clinical research [1,2,4,14,15,[27][28][29][30][31], oocyte cryopreservation has been described to achieve high standards of clinical efficiency [3,6,7,32]. Objective clinical evidence is emerging at a relatively slow pace, because IVF centres that routinely cryopreserve oocytes are still few and, consequently, current data are too small or dishomogeneous to draw definitive conclusions.…”

“…Comparing fresh oocytes with others frozen with a CRSC involving 0.1 mol/l sucrose as an extracellular CPA, Ghetler et al [36] found massive reduction in the number of CG as a effect of cryopreservation, concluding that stored oocytes should be microinjected rather than inseminated by standard IVF to prevent possible fertilization failure secondary to zona hardening. In effect, ICSI (intracytoplasmic sperm injection) had been suggested to be the elective route to achieve fertilization in cryopreserved oocytes [27] and has now become a standard of treatment [6,7,14,29]. The question of a nonphysiological discharge of CG in cryopreserved oocytes remains controversial.…”

“…For example, several lines of evidence have been reported for and against the hypothesis that the metaphase II (MII) spindle can be irreversibly disrupted by low temperature storage [8][9][10][11][12][13]. In effect, during the process of freezing-thawing (or vitrification-warming) the oocyte is exposed to a variety of physical and chemical conditions, such as low or suboptimal temperatures, formation of intracellular ice crystals (IIC), osmotic stress and replacement of intracellular water with cryoprotective agents (CPAs), that may endanger its mere survival [14]. The oocyte's ability to develop into a viable pregnancy may be jeopardized even in the absence of obvious injuries detectable by conventional microscopy [15].…”