July 5, 2007 Scientists in Israel have been able to obtain and freeze eggs from the ovarian tissue of girls as young as 5 years old, the 23rd annual conference of the European Society of Human Reproduction and Embryology will hear on Tuesday (3 July). Dr. Ariel Revel, from the Department of Obstetrics and Gynaecology, Hadassah University Hospital, Jerusalem, Israel, said that the growing number of survivors of childhood cancers meant that such techniques would become increasingly important in preserving fertility in young patients.
Childhood cancers usually result in cure rates of between 70% and 90%, and are generally more responsive to therapy than adult cancers. However, the aggressive chemotherapy which is often necessary usually means that children will be sterile in later life. In adult women, the ovaries are stimulated to produce eggs which are removed, fertilised and frozen.
In younger girls this is not possible, and the method normally used is to freeze the ovarian cortex, which contains the egg-producing follicles, for transplantation at a later date. But the cortex is often damaged by freezing, and collecting and freezing individual eggs from the follicles, which are more resistant to the damage caused by extreme cold, offers a better chance of restoring fertility in adulthood.
To their surprise, Dr. Revel and his team found eggs in the follicles of girls between 5 and 10 years old who had not reached puberty. "We were able to extract oocytes using needle aspiration from very young girls", he said. "For example, we found 7 eggs in a girl of 5 year's old with Wilm's tumour, 8 in an 8 year old with Ewing's sarcoma, and 17 in a ten year old, also with Ewing's sarcoma. We were then able to mature the eggs in vitro and freeze them for use in the future."
The median age in the study group was 16, and eggs were found in all but one patient, herself aged 16. A total of 167 eggs were found, with an average of 8.5 per patient. "Excluding one patient who asked that the oocytes we had found in her ovaries should be frozen immediately, we matured the 130 others in vitro", said Dr. Revel. "41 were successfully matured, a 32% success rate."
"No eggs have yet been thawed", said Dr.Revel, "so we do not know whether pregnancies will result. But we are encouraged by our results so far, particularly the young ages of the patients from which we have been able to collect eggs. We believe that no younger patients have ever undergone egg collection, in vitro maturation, and egg freezing. We are hopeful that the mature eggs can offer these girls a realistic possibility of preserving their fertility."
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