Biological and technical background

There are three hurdles to successfully storing a human egg cell for years or decades and then using it to achieve pregnancy. First, one or more mature, healthy eggs must be retrieved from the woman. As a guideline, the number of eggs required is approximately 10 to 20.

There are three main aspects that are problematic: Usually, only one egg matures per month in a healthy woman, and the quality of this egg decreases rapidly with the woman’s age. For retrieval, an operation under general anesthesia is necessary. In order to protect the woman from many procedures, she will undergo hormone treatment before the procedure to increase the number of jumping eggs per cycle.

As with fertility treatment, the ovary is stimulated. This hormone treatment is usually done with the drug clomiphene in tablet form or the hormones FSH/LH by injection. This drastically reduces the number of necessary collection procedures, so that 2 to 3 collection procedures are now usually sufficient to obtain over 10 “good” eggs for freezing.

The problem remains, however, that the quality of a woman’s eggs steadily decreases after the age of 25. For example, less than 50% of the eggs of a 30-year-old woman are already capable of being fertilised, and less than 20% of the eggs of a 40-year-old woman. The corresponding monthly chances of a naturally occurring pregnancy are about 20% for a 30-year-old woman and about 5% for a 40-year-old.

However, a 25-year-old woman, who would be at the optimal age for egg retrieval, would not normally and obviously see the need for egg screening, nor would she have the financial means to do so. If the desired partner has still not been found beyond the age of 35, or if the professional career is currently the focus of interest, the ticking of the biological clock makes the possibility of cryopreservation look much more tempting. As a result, the average woman who wishes to freeze eggs will have to undergo several cycles of hormonal treatment and egg retrieval procedures to obtain the required number of healthy eggs.

The second hurdle is technical. Freezing is considered the method of choice to allow a biological material to survive for years without natural aging or decomposition by microorganisms putting an undesirable end to its shelf life. The problem: If ice crystals are formed, they penetrate the cell boundaries of the frozen biomaterial because they are sharp-edged.

This irreparably destroys the cells, and when they are thawed, all that is presented is mud. In order to prevent the formation of crystals, cryoprotective agents – so-called cryoprotective agents – are sometimes added and freezing is either very slow (as was previously common) or very fast (new method). During the so-called vitrification process, the cell material is cooled down to approx.

-200°C in hardly more than a second, often with the help of liquid nitrogen. The disadvantage is that the use of partly toxic antifreeze cannot be prevented. The third hurdle after successful retrieval, selection, freezing, thawing and artificial insemination is the task of inserting the egg into the woman’s uterus.

Since successful implantation often does not occur, especially in older women, especially due to reduced blood circulation, it is legally permitted in Germany to implant up to three fertilised eggs at the same time.However, this also leads to an increase in multiple pregnancies. In order to increase the chances of implantation, additional previous hormone therapy may be necessary. A more pronounced mucous membrane of the uterus can then provide a more favourable starting position.