Italian researchers say that they have achieved 13 births using eggs that had been frozen and thawed before being fertilised and implanted into a woman. According to the researchers, who publish their findings in the September edition of the journal Fertility and Sterility, the study indicates that the promise of using unfertilised frozen-thawed eggs is growing, and 'offers new hope' to women who wish to delay having children.
The researchers, from the University of Bologna in Italy, froze 737 eggs taken from 68 different women. Fifty-one of the women were undergoing IVF procedures, but wanted to preserve eggs that were not used in the immediate cycle for potential future procedures. Italian law prevents the freezing of embryos, but does allow gametes - eggs or sperm - to be frozen. The 17 other women wanted to preserve their eggs for future use but had no desired sperm donor at the time. The researchers say that their 'results show oocyte cryopreservation may represent an alternative to embryo storage in selected cases'.
The eggs were frozen for various amounts of time, but calculations showed that about 272 (37 per cent) of them survived the thawing process. Approximately 122 of these were successfully fertilised and 104 of the healthiest were transferred to the women's wombs. Some women did not become pregnant, and three who did become pregnant later miscarried. Thirteen live births were reported among the remaining women.
While sperm and embryos freeze and thaw well, there have been problems in the past with egg freezing, which is not as efficient. The large proportion of water within eggs causes ice crystals to form when they are frozen, causing them to expand and suffer damage. Dr Giovanni Coticchio, leader of the research team, said that a 37 per cent survival rate for the eggs was not good enough, but added that in future studies the team hopes to achieve a 75 to 85 per cent survival rate by altering the medium in which the eggs are stored. They intend to increase the sucrose levels to lower the water content and reduce the likelihood of ice crystals forming. However, this may, in turn, make the eggs susceptible to 'dehydration stress' during the thawing process.
Egg freezing is a technique used primarily by women undergoing cancer treatment, as their ovaries may be unable to produce eggs after treatment. The process of retrieving eggs involves drugs and is uncomfortable and invasive, so it would not ordinarily be contemplated by healthy, fertile women, especially given that the success rate has remained low. If it could be perfected it may allow young women to store their eggs, at the point they are the most fertile, until they are ready to have children. UK fertility expert Simon Fishel, director of the Centres for Assisted Reproduction, said egg freezing is technically problematic and was costly, inefficient and uncomfortable for the patients. 'Freezing is still at the experimental stage so women have tended to use it only if they are undergoing medical treatment', he said, adding 'but if the technique improves they may start to choose it for lifestyle reasons'.