The freezing of human eggs with the ability to thaw and fertilize them at a later time has been something that we have been trying to do for many years.
Women of reproductive age who acquire a form of cancer necessitating chemotherapy as treatment may choose to freeze eggs. Many of the chemotherapeutic drugs used to treat breast cancer for example, may result in loss of fertility due to the toxic effects they have on eggs, leaving the women effectively menopausal after treatment. These women may choose to have a group of eggs retrieved from their ovaries and frozen prior to starting chemotherapy thus preserving their ability to get pregnant later.
Some women have religious, ethical or moral beliefs regarding the storage of embryos which prevent them from doing IVF. For these women, although a group of eggs may be retrieved, not all of them need to be fertilized at the same time. The number of eggs which would be used for transfer could be fertilized and the rest frozen. That way, no extra embryos that may not be used would be frozen and the rest of the eggs could be thawed out in limited numbers later if needed.
Occasionally, during an IVF cycle a situation arises where sperm may not be available on the day when the eggs need to be fertilized. This might occur if the man is unable to produce a specimen due to anxiety or illness or if for an unforeseen circumstance he is not in town and a backup specimen is not available. The eggs could then be frozen and used later when the sperm becomes available.
The use of egg freezing may be useful for obtaining and storing eggs from egg donors. At present, most egg donation cycles involve the simultaneous stimulation of the egg donor and preparation of the recipient’s uterus. This may be inconvenient for one or the other of these women or sometimes the eggs are ready to be retrieved before the recipient’s uterus is ready to receive them. If the eggs from potential donors are obtained and frozen in advance, a donor egg bank could be created which would make the process more convenient.
We have recently completed a study in our laboratory comparing the two different freezing methods that are currently available. We used eggs obtained from egg donors and demonstrated as others have, that one method (MicroSecure Vitrification) was far superior to the other method (Slow freezing). Using vitrification in this study we had an egg survival rate of 90% after thawing with subsequent 81% rate of fertilization. We transferred an average of just over 2 embryos per patient and obtained an implantation rate of 39% and a live birth rate of 47%. All the babies were born healthy and had normal child development checkups at their 1 year exams. Since then, the technology has been offered to patients with similar success.
Therefore we feel that egg freezing is a technology whose time has finally come and we are happy to offer this procedure to our patients when appropriate.