For decades, it was thought that whichever sperm was strongest, and luckiest, would be the one to fertilize the egg. Fertilization was framed as a competition: millions of sperm racing toward a passive egg, with the fastest winner taking all.
But newer research is revealing something far more nuanced.
Scientists are now discovering that the egg may play a much more active role in fertilization than we ever realized, through a process known as cryptic female choice. Fertility, it turns out, is not just about speed or strength. It’s a biological dialogue. It takes two to tango, and the evolving story of the egg and sperm reflects just how intricate that dance truly is.
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Does the egg choose the sperm?
Cryptic female choice and sperm guidance
Rather than waiting passively for sperm to arrive, the egg appears to participate in the selection process. Through a phenomenon called sperm guidance, or sperm chemotaxis, the egg releases chemical signals, known as chemoattractants, that help guide sperm toward it.
These signals don’t act indiscriminately. Instead, they appear to influence which sperm are able to respond and how effectively they move.
How sperm chemotaxis works
Research suggests that chemoattractants may affect sperm motility, helping certain sperm swim faster and more efficiently. Sperm that are a better biological match may be more responsive to these signals, increasing their likelihood of reaching the egg.
In other words, the egg may be helping to narrow the field by favoring sperm with the best genetic compatibility rather than simply the strongest swimmer.
Why genetic compatibility matters
This emerging science reframes fertilization as a collaborative process rather than a race. But before sperm ever have the opportunity to respond to these chemical cues, they must survive a remarkably difficult journey just to get close enough to the egg.
Understanding what sperm must overcome helps us appreciate why sperm health before conception matters so much.
Men's Prenatal
Why sperm health matters before conception
Before a single sperm can receive guidance from the egg, it must navigate a series of biological obstacles, many of which eliminate the majority of sperm long before fertilization is even possible.
When sperm health is compromised, fewer sperm make it far enough to participate in this selection process at all. This is why supporting sperm quality before trying to conceive is a critical, and often overlooked, part of fertility preparation.
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Is there a fertility crisis? Understanding declining sperm counts
What is a healthy sperm count?
In men with healthy fertility, the average sperm count per ejaculate typically ranges from 180 to 400 million sperm. This large number isn’t accidental, it reflects the many barriers sperm must overcome on their way to the egg.
Are sperm counts really declining?
Over the past several decades, multiple studies have reported declining average sperm counts worldwide. Some estimates suggest that today’s average sperm count may be roughly half of what it was 50 years ago, though some experts note that the data remains debated.
What is consistent, however, is the observation that sperm health has not declined uniformly across the globe.
Environmental factors and sperm motility
Regions with lower pollution exposure appear to have experienced less dramatic changes in sperm count. Additionally, declines in sperm motility, the ability of sperm to move efficiently, have also been observed in recent years.
Together, these trends suggest that environmental and lifestyle factors may be playing a meaningful role in modern male fertility.
The sperm’s journey to the egg
The five biological barriers sperm must overcome
For fertilization to occur, sperm must successfully complete all of the following steps:
- Travel from the testicles through the vas deferens and urethra. Some research suggests that up to 30% of men have abnormal semen parameters due to poor sperm quality, making this first step difficult or impossible.
- Survive the acidic environment of the vagina.
- Navigate cervical mucus, which changes in texture throughout the menstrual cycle.
- Choose the correct fallopian tube, depending on which ovary released an egg that cycle.
- Penetrate the egg, which is surrounded by a thick layer of protective cells. Sperm release enzymes to break down this layer, often requiring the assistance of multiple sperm so that one can ultimately enter.
How many sperm actually reach the egg?
Out of hundreds of millions of sperm, only about 200 typically make it through all of these barriers to reach the egg. And even then, only one sperm can fertilize it.
This makes sperm quality, not just quantity, absolutely essential.
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Swimming upstream: Why sperm have so much working against them
Sperm must overcome harsh environments, biological checkpoints, and modern lifestyle stressors. And because today’s average man may already be starting with fewer healthy sperm than previous generations, every advantage matters.
This is why fertility experts often recommend that men begin making intentional lifestyle and nutrition changes at least three months before trying to conceive. That’s how long it takes for sperm to fully develop and mature.
How to support Strong, healthy sperm
Key lifestyle and nutrition strategies to improve sperm quality
Research shows that the following strategies can help improve sperm count, motility, morphology, and DNA integrity:
Take a comprehensive men’s fertility supplement
Even with a nutrient-dense diet, modern environmental exposures and depleted soil nutrients can make it difficult to meet fertility-related micronutrient needs.
Key antioxidants and nutrients, including vitamins C and E, CoQ10, selenium, zinc, N-acetyl-L-cysteine (NAC), and L-carnitine to support sperm DNA integrity and healthy motility. WeNatal for Him was formulated specifically to meet these needs during preconception.
Reduce exposure to environmental toxins
Environmental toxins are a major contributor to sperm damage. Supporting sperm health starts with the basics: clean drinking water, fresh air, and minimizing chemical exposure.
Choosing organic foods when possible, reducing plastic use, and avoiding cigarette smoke, vaping, excessive alcohol, and recreational drugs can all make a meaningful difference. WeNatal’s Preconception Guide offers additional strategies to reduce toxic burden.
Follow a fertility-supportive diet
Men who closely follow a Mediterranean-style diet which is rich in vegetables, fruits, whole foods, healthy fats, and lean proteins, have been shown to have higher sperm concentration, improved motility, and healthier sperm morphology.
Manage stress to support hormone health
Chronic stress can interfere with the hormones required for sperm production and maturation. Regular stress-reduction practices, balanced exercise, adequate rest, and professional support when needed all contribute to healthier reproductive function.
Avoid excess heat exposure
Prolonged heat exposure has been linked to reduced sperm quality through increased oxidative stress and genetic damage. Avoid placing laptops directly on the lap, carrying phones in front pockets, frequent hot tub use, and wearing overly tight underwear or pants.
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A note from WeNatal on supporting men’s fertilityÂ
The journey to conception is truly a two-person effort. While maternal health has long been emphasized in fertility conversations, we now understand that sperm health plays an equally vital role, and that the egg itself may help choose the sperm it wants.
At WeNatal, we believe in supporting fertility for both partners with science-backed prenatal supplements and education designed to optimize reproductive health long before conception occurs. By making intentional nutrition and lifestyle choices, couples can create a stronger foundation for a healthy pregnancy and baby.
Your fertility journey starts with both of you. Let’s make it a strong and healthy one, together.
References
Fitzpatrick JL, Willis C, Devigili A, et al. Chemical signals from eggs facilitate cryptic female choice in humans. Proc Biol Sci. 2020;287(1928):20200805. doi:10.1098/rspb.2020.0805
Jørgensen N, Lamb DJ, Levine H, et al. Are worldwide sperm counts declining?. Fertil Steril. 2021;116(6):1457-1463. doi:10.1016/j.fertnstert.2021.10.020
Pasqualotto FF, Sobreiro BP, Hallak J, Athayde KS, Pasqualotto EB, Lucon AM. High percentage of abnormal semen parameters in a prevasectomy population. Fertil Steril. 2006;85(4):954-960. doi:10.1016/j.fertnstert.2005.09.032
RamÃrez-Gómez HV, Jimenez Sabinina V, Velázquez Pérez M, et al. Sperm chemotaxis is driven by the slope of the chemoattractant concentration field.Elife. 2020;9:e50532. Published 2020 Mar 9. doi:10.7554/eLife.50532
