New Research Finds That Eggs Choose Sperm

With all of the information we have about our bodies, and fertility in particular, sometimes it almost seems like there’s nothing new to discover. We’ve researched, investigated, hypothesized, and studied so much that, most of the time, we feel like we have all the answers and all the information we could ever need.

By Gwen Farrell4 min read
New Research Finds That Eggs Choose Sperm

The truth is, there’s so much information we don’t even realize we don’t know, especially when it comes to fertility, and the abilities of our male and female biological functions. We tend to view these things in very distinct, separate ways: eggs can only do this, sperm can only do that. That’s not entirely correct, though.

New research from Stockholm University and the Manchester University NHS Foundation Trust put a specific theory into practice, and the results were absolutely fascinating. Their findings have the potential to change not only fertility and infertility practices, but our conversation on the female body and its inherent capabilities. 

What You Don’t Know about Eggs

When it comes to conception, we might view the female role more as passive rather than active. We were told in our high school biology and sex education classes that the egg is fertilized by the sperm to create the embryo, and beyond that not much more. 

That is basic biology, yes, but it creates a pretty limiting understanding of the abilities of our female reproductive systems, as if conception is just something that happens spontaneously to us and not a function we have a critical part in. Part of that misunderstanding probably comes from what we know (and what we don’t know) about eggs. 

Most of us know that women are born with all the eggs we will ever have. But beyond that, we probably don’t know much. For instance, we’re born with all our eggs, but that number is estimated to be around 200 million. As we enter puberty, the number of viable or usable eggs declines to around 400,000 or less, and we lose 1,000 immature eggs for every one egg that is ovulated per cycle. The craziest part is that the number of eggs we lose is beyond anything we can control or influence. 

We’re born with all our eggs, but that number is estimated to be around 200 million.

You’ve probably heard that women in their late 30s have a hard time conceiving, and the possibility of conception becomes even more difficult to achieve as they enter their 40s. There’s biology to back that up. It’s because the quality of our eggs decreases with age, and even more after age 35. A decline in fertility in our early middle-age is perfectly natural though, because the number of eggs left remaining isn’t that much. While 90% of our eggs are viable in our early 20s, only 10% or so are viable as we enter our 40s. This brings a whole new understanding to the term “biological clock.”

If you’re concerned about getting pregnant at an older age, don’t worry too much! All it takes is one healthy egg. Some supplements to improve egg quality are Vitamin D, Alpha Lipoic Acid, and Co-enzyme Q10. You will want to start taking these supplements for several months before trying to get pregnant.

Because women are born with all the eggs they will ever have, including the ones that will be fertilized to create embryos, this means that we at one time were part of our mother’s and even our grandmother’s supply of eggs. To picture it better, as our grandmother was pregnant with our mother, we were partly contained in the unfertilized eggs in our mother’s ovaries she developed as a fetus. More than just one egg and one sperm played a part in creating each of us as individuals, which is pretty incredible to think about. 

What You Don’t Know about Sperm

If our mainstream understanding of eggs is that they don’t do a whole lot, our understanding of sperm is the exact opposite. There's a good reason for this, after all. Without sperm, an egg can’t be fertilized and an embryo can’t be created. But perhaps we give sperm a little more credit than they actually deserve. 

Additionally, if we know the bare minimum about our eggs, we know probably even less about sperm. 

Sperm are actually extremely sensitive to the environment and lifestyle choices of a man. Studies found that men with active lifestyles and diets that include high Omega 3 content have better shaped sperm. The shape of the sperm is essential because it enables strong motility, or movement, which is vital for the long journey through the vaginal canal to the Fallopian tubes to cause conception. Regular sex is also important in keeping sperm healthy and active. It’s estimated that a healthy male can produce around 12 billion sperm per month. 

Men with active lifestyles and diets that include high Omega 3 content have better shaped sperm.

Just as healthy lifestyle choices can assist in creating healthy sperm, poor lifestyle choices and habits can severely damage sperm. Habits like being sedentary or smoking can result in sluggish or poorly-formed sperm, which can in turn create deformed or abnormal specimens and low motility. However, men can make definitive diet and exercise choices which can greatly improve the quality of their sperm. 

While the quality of sperm does decrease somewhat with age, as do the quality of our eggs, they don’t decrease in the same way, and older men can still have good quality specimens capable of making the trip, so to speak. 

Eggs Choose Sperm, Not the Other Way Around

To recap: Up until now, we’ve thought that the sperm are solely in charge of fertilizing the egg and the egg essentially sits back and does nothing, for all intents and purposes.

But this latest study from Stockholm University and the NHS Foundation Trust at Manchester University have proven that particular understanding is far from accurate. 

The research, which used tons of variant combinations of eggs and sperm from 60 separate couples undergoing IVF, found that eggs release what’s known as a chemoattractant, which basically acts as a glaring neon sign for the egg to draw attention to itself. If it likes the sperm, the egg will release the chemoattractant, encouraging the sperm to swim faster towards that egg to fertilize it. If the egg doesn’t like the sperm, it will release a different signal, causing the sperm to slow down. This explained why the eggs released chemoattractants when introduced to some specimens, but didn’t when introduced to others. 

If the egg likes the sperm, it will release the chemoattractant, encouraging the sperm to swim faster. 

Here’s where things might get awkward. Dr. John Fitzpatrick, a key investigator in the research, explained that while this enables the egg to choose the specimen it’s most genetically and biologically compatible with, it might not always choose the sperm belonging to the partner the woman has chosen. However, the research has been called a “fertility game changer” because it allows us to see that eggs play a much more elective role than we previously thought. What’s more, Dr. Fitzpatrick clarified that sperm have one job — to fertilize the egg — but it’s the egg that gets to choose the specimen that’s the best quality for that fertilization. 

Closing Thoughts

Pregnancy is already complicated enough when it comes to the exact parameters and environment that’s ideal for creating a baby. But there’s beauty in that complexity, especially in realizing that our natural biology knows what’s best for us better than we consciously do ourselves. 

Dr. Fitzpatrick said it best: “Interactions between human eggs and sperm depend on the identity of the women and men.” For all our fertility concerns over biology and genetics, the issue is, essentially, more an emotional decision than we thought. In this understanding, it’s clear to see that our eggs are looking out for us and want what’s best for us. This research can also provide crucial information and more solutions for couples who might have previously misunderstood issues when it comes to their infertility.

While this research is exciting enough to think about from a scientific standpoint, there’s also a sense of certainty and assurance it can provide us as individuals. We just have to cross our fingers and hope that the partners we’ve chosen are the ones our eggs want us to choose.

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