1, which women are suitable for oocyte cryopreservation?
ASRM supports oocyte cryopreservation for medical reasons (mainly for young women who suffer from cancer and will lose their fertility after chemotherapy); It does not support large-scale self-freezing of eggs in order to delay the birth time.
In the investigation of nearly 65,438+0,000 literatures, ASRM only found four randomized controlled trials of cryopreservation of fresh eggs and oocytes, and they mainly came from the clinical data of young egg providers with high pregnancy probability, rather than the more common clinical data of women in their thirties. Therefore, ASRM concluded that women should not rely on oocyte cryopreservation to delay childbearing age, because "there is no data to prove that this kind of oocyte cryopreservation behavior is safe, effective, ethical, low in emotional risk and cost-effective."
This has become catch-22 from oocyte cryopreservation: until enough early adopters participate in the experiment, its real effectiveness can only be unknown.
Of course, in front of young women who want to avoid the risk of childbirth, ASRM's statement is still too cautious to really arouse their thinking. In fact, in the past few years, many fertility clinics in ASRM have actively supported the self-freezing of eggs. 20 10, 143 fertility clinics claimed that they could provide oocyte cryopreservation, of which 63 provided independent oocyte cryopreservation. PasqualePatrizio, the head of YaleFertilityCenter, which provides self-oocyte cryopreservation, said that this is a promising technology (the institution is not a member of the Egg Bank). Patrizio repeated a common argument: when a woman freezes an egg, she freezes the chance of getting pregnant with that egg. After seeing some definite data at the ASRM annual meeting, he said, "More data will appear soon."
Dr NicoleNoyes, from the Reproductive Center of new york University, provided the above data: Through oocyte cryopreservation technology, there have been 62 births or pregnancies in the Reproductive Center of new york University, with a success rate of 44%. Compared with the success rate of in vitro fertilization of 1/3, this result is very attractive. In these 62 cases, 365,438+0 women used their own eggs. In these cases, the probability of successful pregnancy in a physiological cycle is 42% for patients who use oocyte cryopreservation aged 25-34, while the success rates for patients who use oocyte cryopreservation aged 35-40 and oocyte cryopreservation aged 4 1-42 are 37% and 33% respectively.
Noyce said that she might revise the above results more conservatively. In order to be safer, women should freeze 20 eggs at a time of pregnancy; If they are close to 40 years old, it takes about three physiological cycles to get enough eggs. In other words, women who want to get pregnant in this way need to pay a lot of time and energy, and of course, money. At the Reproductive Center of new york University, a set of cryopreservation procedures for oocytes, plus two-year storage period and three-time thawing of eggs, currently costs about 39410 ~ 46,560 dollars.
2. What are the risks in oocyte cryopreservation?
For many people, oocyte cryopreservation seems to be a "doctor's advice" thing. However, in this debate, people have neglected the influence and risks of oocyte cryopreservation, which is not clear. After all, egg freezing is still a new technology.
So far, only 2,000 babies in the world have been born through low temperature oocyte cryopreservation. According to early data, oocyte cryopreservation is the best choice for women to have children after the age of 40, but describing oocyte cryopreservation as a reliable maternity insurance will make women rely too much on this constantly improving technology.
Oocyte cryopreservation's technical difficulty lies in thawing eggs. "I have asked oocyte cryopreservation about hundreds of caring women." MichaelTucker, chief embryologist of Shady Grove Reproductive Medicine Center and DonorEggBankUSA, said. Since he published an article about the old-fashioned egg freezing technology in 1997, he has been found by phone all over the world. At that time, embryologists were still using the "slow freezing method", and he and others in this field gradually found that this method was not reliable. As the largest cell in the human body, the egg is highly mobile. Ice crystals will form when frozen, and they will crack eggs when thawed.
In the late 1990s, scientists began to develop a new "vitrification freezing method". Firstly, the eggs are dehydrated, added with antifreeze, and then quickly frozen at low temperature to prevent them from forming ice crystals and improve the chances of successful thawing. In the past ten years, vitrification has largely replaced slow freezing. With it, Tucker can "say with more confidence: Yes, we can provide stable and high-quality fertility services".
The 200 babies born by oocyte cryopreservation technology in the Shedi Grove Reproductive Medicine Center support this statement, but Tucker, like other doctors, thinks that the success of oocyte cryopreservation has a lot to do with the choice of institutions. Vitrification requires considerable skill. Tucker said that this process requires coordinated operation and accurate judgment of the operator. He added: "We have 26 embryologists, and I only trust the vitrification technology of six of them, and four of them will soon be competent." Tucker, who is in charge of the national vitrification surgery training program, said he thought it would take at least four years for all clinics to provide stable results. "It sounds a bit boastful," Tucker admitted, but he was not the only one who made such a cautious assessment.
The American Association for Reproductive Medicine (ASRM), which is responsible for the self-regulation of fertility institutions in the United States, is not prepared to support the commercialization of cryopreservation of oocytes. In 20 12, ASRM removed the label of "experimental" from oocyte cryopreservation due to the success and relative safety of vitrification.
For women, the main risk in the process of egg freezing is ovarian hyperstimulation syndrome caused by ovulation induction drugs. It will cause edema, and in more serious cases, urinary tract obstruction and bleeding will occur. According to ASRM, if embryo transfer is not done, the probability of ovarian hyperstimulation syndrome is very low: only about 0.4% ~ 2% of women who use ovulation induction drugs will develop severe ovarian hyperstimulation syndrome.
More seriously, the long-term health risks faced by babies born by cryopreservation of oocytes have not been confirmed. This technology is so new that there is not enough long-term research to support it, but ASRM lists some positive results in recent research.
3. The cryopreservation process of oocytes.
As far as cryopreservation technology of oocytes is concerned, it has undoubtedly brought good news to many women. Whether it's leftover women or strong women who don't want to have children so soon, they can keep their fertility when they are young through oocyte cryopreservation. Let's look at the process of cryopreservation of oocytes.
The reproductive technology of cryopreservation of oocytes may be completed by only one operation for young women in their thirties. They usually go to the clinic in the morning, and doctors collect all the eggs in women's ovaries after anesthesia. Rest for an hour after waking up, and you can go home if there is no problem.
Before taking eggs, women who take eggs need to take ovulation-promoting drugs to make multiple follicles develop ahead of time, and use puncture technology to expel multiple eggs, so as to obtain multiple eggs at one time.
Preserved eggs should be pretreated in cryoprotectant after they are taken out of women's bodies. The main purpose is to dehydrate the eggs. At present, there are mainly two kinds of freezing methods at home and abroad: one is programmed freezing, that is, cooling and freezing under the specific setting of programmed freezer, and finally storing in liquid nitrogen; The other is ultra-high-speed vitrification, in which eggs are pretreated in cryoprotectant and then directly frozen in liquid nitrogen at a very high speed.
Thawing (resuscitation) When an egg that was originally frozen needs to be conceived, it needs to be thawed. This thawing and recovery process needs to be carried out quickly. Generally, eggs are directly taken out of liquid nitrogen to room temperature, and protective agents are used. The eggs that survive after resuscitation can be fertilized in vitro by in vitro fertilization or intracytoplasmic sperm injection (ICSI), and then transferred to embryos.
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