How Are Sperm And Eggs Frozen For Years?

If you paid attention in your biology class in high school, you surely know that babies are made when a male’s sperm connects with a female’s egg. Hundreds of millions of sperm vie for a single goal, all swimming to meet their single target: the egg.

Although there are millions of sperm in the race, it only takes one sperm hitting the egg for the female to be impregnated and nine months later, along comes a baby!

You might know the basics of all this, but do you know that eggs and sperm can actually be frozen for years and used later when they’re eventually required? That’s right, they can be stored safely for years!

How does that work? Since sperm and eggs are essentially cells, doesn’t prolonged freezing affect their ‘effectiveness’? If it doesn’t, then can the same reasoning and techniques be applied to ‘preserving’ entire human bodies, i.e., freezing bodies and reviving them many years later?

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Cryopreservation: Sperm or egg freezing

No matter how healthy your lifestyle is or how fit you are, your fertility is bound to decline with age, regardless of whether you’re a man or woman, with a steep decline in the age range of 35-45 years. The fall in egg (or sperm) quality occurs earlier for some people and later for others.

Now, a decline in the quality of eggs is associated with increased risks of chromosomally abnormal babies or miscarriages. A workaround for this situation is oocyte cryopreservation.

Cryopreserving ovarian tissue strips Cryopreservation Egg freezing

Cryopreservation is a good alternative for patients postponing pregnancy. (Photo Credit : Wzsuzsanna3 at Hungarian Wikipedia; Dr. Vereczkey Attila / Wikimedia Commons)

Simply put, cryopreservation is the freezing of tissue for future use. Since frozen sperm cells, eggs (oocytes) and embryos do not age, fertility (of the individual in question) can be maintained, regardless of medical or other issues.

Furthermore, this is not for just a few years; eggs can be frozen indefinitely. This is why a woman can freeze her eggs as an effective means of protecting her fertility in the future. In addition to that, freezing excess embryos reduces the cost of subsequent assisted pregnancies (when the woman grows old and is not as fertile as she was in her youth).

Why do people choose to freeze their eggs?

As mentioned earlier, the biggest advantage of freezing eggs is that it helps preserve a woman’s fertility into the future. Now, this is the advantage, but why do people choose to freeze eggs/sperm in the first place?

Frozen sperms

Freezing sperm preserves future fertility. (Photo Credit : USDA Gene Bank / Wikimedia Commons)

Well, there are a few reasons, including the fact that some people might want to postpone reproduction for medical reasons. For instance, if a person is about to enter chemotherapy, they might want to freeze their eggs/sperm so that they can be used in the future, because cancer therapies might reduce future fertility (Source).

There are many people who postpone reproduction for personal reasons too. It’s interesting to note that among the first wave of ‘egg freezer’ women (from the years 2005 to 2011), more than 80% did not have a partner. There are a couple of reasons behind that too, and one of them is that modern women have more demanding careers, which they want to focus on before they involve themselves in the process of childbearing.

How can eggs remain frozen for so long without losing their effectiveness?

One might wonder as to how eggs/sperm cells can remain frozen for so long without losing their ‘oomph’. Wouldn’t the freezing and subsequent thawing years later somewhat compromise its effectiveness?

Well, firstly, eggs and sperm cells don’t have much water content in them to begin with. Therefore, they’re not under a major threat of getting ruptured/ruined during the freezing-thawing process.

Sperm cells

Sperm cells and eggs are resistant to super-low temperatures, as they’re too small and don’t have much water in them. (Photo Credit : Flickr)

Also, they’re very small (as they are just… cells). Thus, they are quite resistant to environmental stress (e.g., super-low temperatures).

Despite all of this, some cells do get damaged during the freezing-thawing process. However, that’s not that big a deal because, in a sperm sample, where you have millions of sperm cells, even if you ruin 10% of the total count, you still have plenty left to get the job done. After all, it only takes one sperm cell to hit the target egg cell.

This is part of the reason why it’s okay to freeze and then thaw a sperm cell, but not an entire human body. Just like a single brick is more likely to ‘survive’ a tornado than a tall building, similarly, a single sperm/egg cell has marginally better chances of surviving the process of freezing-thawing than a full-blown human body. This is because a human body is an insanely complicated structure, and also, composed of ‘70% water’. As a result, it’s bound to rupture a great deal of cells during the freezing-thawing process. If a human body loses 10% of its cells, say, from the brain, as the result of cryopreservation, then the individual in question can kiss their chances of revival goodbye.

That’s why it’s perfectly okay to freeze egg cells and sperm cells indefinitely, but the same reasoning and technique won’t work on something as complex as a human.

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About the Author

Ashish is a Science graduate (Bachelor of Science) from Punjabi University (India). He spearheads the content and editorial wing of ScienceABC and manages its official Youtube channel. He’s a Harry Potter fan and tries, in vain, to use spells and charms (Accio! [insert object name]) in real life to get things done. He totally gets why JRR Tolkien would create, from scratch, a language spoken by elves, and tries to bring the same passion in everything he does. A big admirer of Richard Feynman and Nikola Tesla, he obsesses over how thoroughly science dictates every aspect of life… in this universe, at least.

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