Orthotopic and heterotopic autografts of frozen-thawed ovarian cortex in sheep

Freezing ovarian cortex is a new option to preserve the fertility of young patients undergoing cancer treatment or in women facing premature menopause . However, the best way to use this banked tissue remains unclear. The func tion of heterotopic and orthotopic autografts of frozen-thawed ovarian cort ex of sheep was compared in the present study. Fresh and frozen-thawed frag ments of ovarian cortex were autografted on the uterine horn of six ewes (o rthotopic grafts) and under the skin of the belly in nine ewes (heterotopic grafts). In both orthotopic and heterotopic grafts, the resumption of foll icular growth and ovulation was monitored. In orthotopically grafted ewes, fertility was recorded. Oocytes from both types of grafts were collected, m atured and fertilized in vitro, In both fresh and frozen-thawed grafts foll icular growth resumed normally; preantral and antral follicles were first d etectable 4 and 10 weeks respectively following grafting but only 5% of the primordial follicles appeared to have survived. This confirms that graftin g procedures are more deleterious for follicle survival than cryopreservati on, Although ovulation resumed in most ewes, none of the ewes grafted ortho topically became pregnant at a synchronized mating, Seven months following grafting, oocytes could be collected from heterotopic and orthotopic grafts , matured and some of them fertilized, but none developed to the blastocyst stage. Heterotopic grafting may be an alternative to orthotopic grafting t o preserve fertility provided follicle survival in the grafts is markedly i mproved.