Freezing eggs is not a good way to delay childbirth.

Technology companies (mainly IT enterprises) have always been considered to be at the forefront of the times. Their corporate benefits are envied by many employees in traditional industries for their [humanization] and [regardless of cost] characteristics. [Apple and Facebook will pay for the frozen eggs of their female employees] have even been praised by netizens as [the strongest corporate benefits]. However, is it really good to pay for oocyte cryopreservation?

I. Egg Freezing: When Demand Encounters Technology

1. Eggs are scarce and fragile

Mammalian eggs are very fragile. In vitro conditions, without suitable conditions, the eggs can cause irreversible damage in a short period of time until they die. Moreover, eggs are relatively scarce. Generally, sexually mature women discharge one mature egg a month.

2. Poor egg quality of elderly women

Studies in reproductive medicine point out that the older a woman is, the worse the quality of the egg she produces. This [difference] is reflected in: the probability of chromosome abnormalities in eggs produced by elderly women will increase; After the egg is fertilized to form an embryo, the developmental potential of the embryo is also relatively poor. Abnormal chromosome of the embryo will lead to abortion, neonatal defects and other problems. Poor embryonic development potential will lead to problems such as difficulty in pregnancy.

3. More elderly parturients

Compared with the previous 100 years or even the first 50 years, Modern lifestyles have changed dramatically. Statistics show that the proportion of women who have children between the ages of 35 and 39 has increased by 150% since 1970. Lifestyles change is somewhat out of harmony with the inherent fertility characteristics of human beings, which is manifested in: some jobs even potentially exclude female job seekers because women need to have children; Modern women are constantly postponing their childbearing age due to academic and workplace pressures. More and more elderly parturients are aged 30 or even 35.

Therefore, people will naturally think that it is not very good to freeze the high-quality eggs from a young age, thaw the high-quality eggs when appropriate, and then make test-tube babies. In a Bloomberg Businessweek article entitled “Oocyte Cryopreservation, Liberation Cause”, it is said that [since the birth control pill came out, no medical technology has such great potential to change family and career planning as oocyte cryopreservation].

There is no denying that egg freezing has a significant role in promoting women’s rights. However, relying on the current egg freezing technology to support one’s career planning is not so reliable.

Second, egg freezing: the theory is very simple, the reality is very bony

In practice, egg freezing is to collect a certain amount of mature eggs and freeze them in liquid nitrogen by using [controlled ovarian hyperstimulation, COH] technology, thus achieving the purpose of long-term preservation. In liquid nitrogen, the metabolic activities of eggs tend to stop. Theoretically, there is no time limit for cryopreservation.

1. Professional techniques for egg freezing

There are two kinds of common egg freezing techniques: [slow freezing] and [vitrification]. Slow freezing has been abandoned by most laboratories because of its expensive equipment and time-consuming and laborious. Most of the eggs now are frozen by vitrification.

Both techniques require adding some antifreeze protectants to the culture solution. Some antifreeze protectants are toxic, but so far, no adverse reactions have been found in clinical application. However, embryologists dare not take it lightly. Relevant research continues and relevant debates have not subsided.

[Vitrified oocyte cryopreservation] The procedure is simple, Put the egg in a hypertonic solution, Then put it into a freezing tube and put liquid nitrogen into it. Its principle is: Taking advantage of the difference in the concentration of total substances inside and outside the cell, Let the high concentration of antifreeze protective agent added in the vitrification solution penetrate into the inside of the egg, At the same time, the water in the egg is replaced. At this time, the cell contains less water, the viscosity of the cell increases, and it is put into liquid nitrogen to cool rapidly, which will cause the liquid in the egg to change from liquid to semi-solid and then to solid, and show a transparent state, which we call [vitrification].

2. Ice Crystal Damage

However, whether it is an egg or an embryo, the most fearful thing is that during freezing, the water in the culture solution and cells forms ice crystals.

[Ice Crystal] is a physical concept, that is, fine pieces of ice. When ice crystals appear during freezing, the cell structure will be mechanically damaged, just like being cut by a knife, thus causing irreversible damage to the egg/embryo.

In fact, the freezing effect of eggs is worse than that of embryos. Because eggs are larger than individual cells in embryos, they are not easily dehydrated during freezing and are more likely to form ice crystals. In addition, eggs are single cells, unlike embryos, and can continue to develop even if some cells are damaged.

Third, egg freezing: tomorrow’s hope, the current truth

It must be admitted that egg freezing has its natural benefits. However, the current technology is really not mature enough.

1. Hope of fertility

It can help patients who need radiotherapy or ovariectomy. Such people must freeze their eggs before they can have any hope of giving birth.

In some countries where freezing embryos is prohibited by law, this is the only way to preserve fertility.

Clinically, couples who have already obtained eggs but cannot obtain sperm on that day should freeze the eggs and reuse them after obtaining sperm instead of discarding them.

The above situation is a last resort. Whenever there is a choice, frozen embryos are much more mature.

As for those who want to delay giving birth, those who are already married can choose frozen embryos. If no object wants to preserve eggs, it seems that preserving eggs is the only legitimate reason for oocyte cryopreservation.

2. Egg freezing will lead to a significant decrease in clinical pregnancy rate.

However, oocyte cryopreservation technology is not so mature now.

After the eggs are frozen and thawed, The zona pellucida of the egg hardens, and conventional in vitro fertilization (IVF, i.e. The first generation IVF technology) is not a good choice. Generally, intracytoplasmic injection of single sperm (ICSI, i.e. The second generation IVF technology) is required. Even if ICSI is done, there may be events such as non-cleavage of the egg after fertilization, slow embryo development and poor embryo implantation ability.

3. The Recovery Rate Game of Commercial Companies

Some companies claim that [more advanced vitrification technology] is full of gimmicks, and [the recovery rate of eggs after freezing is above 90% (or 92%, 95%, 99%, etc.), which is even more confusing to many people.

In fact, although vitrification freezing technology is simple and easy to use, it cannot overcome egg damage caused by freezing. The recovery rate refers to the number of surviving eggs divided by the number of oocyte cryopreservation after thawing. Such a high recovery rate is in line with the truth, but what businesses deliberately hide is the problem that the ability of eggs to continue to develop after freezing and thawing is greatly reduced.

4. Avoiding the risks of policies and regulations

Due to relevant policies and regulations, There is no egg bank in China, Unmarried women cannot freeze their eggs at home. Some organizations that promote egg freezing come from abroad. Most of them talk about good conditions to take women abroad for egg freezing. Two points I want to emphasize are that Don’t be fooled by the implication in the advertising slogan that [domestic technology is not good], Freezing eggs is not difficult to operate. People with experience in embryo operation can operate after an hour of training. It is not difficult to understand in theory, and there is no [black technology] in technology at present. Another point is to carefully investigate the qualification of the institution implementing the technology. The profit of egg freezing is relatively high. The newly established commercial company is likely to follow the trend and start in a hurry, lacking clinical and laboratory experience.

IV. Egg Freezing: No Guaranteed Delayed Fertility [Good Prescription]

With the change of modern life style, Women’s need to delay childbirth is becoming more and more obvious. Giving birth to healthy babies is contrary to [elderly mothers]. Oocyte cryopreservation technology seems to solve this problem perfectly in theory. However, As far as the current technology implementation is concerned, The technology of oocyte cryopreservation is not mature enough, Although it is not difficult to operate, However, it is generally believed in the industry that the pregnancy rate of frozen eggs cannot reach the level of clinical application. Women who hope to preserve fertility through this way need to remember: oocyte cryopreservation technology cannot give you a safe and reliable guarantee, that is to say, it is absolutely possible or likely to give birth to children after not freezing eggs.