Scientists are investigating a fascinating and often overlooked part of conception: what happens to sperm after it enters the female reproductive tract. The findings could eventually help us better understand why some people experience unexplained infertility.
When you’re struggling to conceive, fertility investigations often seem to come down to two separate questions.
Are the eggs healthy?
And:
Is the sperm healthy?
But new research is looking at something that happens between the two – and it could change the way scientists think about fertilisation.
Researchers in the United States are investigating how the female reproductive tract interacts with sperm after sex and whether those interactions could influence a sperm’s ability to survive and ultimately fertilise an egg.
It raises a fascinating possibility.
Sometimes it may not simply be about the sperm or the egg individually.
It could also be about how they interact.
What happens to sperm inside the female reproductive tract?
We tend to think of sperm as having one job: swim towards an egg and fertilise it.
In reality, the journey is much more complicated.
Once sperm enter the female reproductive tract, they encounter a constantly changing biological environment.
That environment can affect whether sperm:
- survive
- remain healthy
- have enough energy
- function normally
- become capable of fertilising an egg
Scientists already know that the female reproductive tract plays an important role in this process.
What they don’t yet fully understand is exactly how these interactions work at a molecular level.
And that’s what researchers are now trying to uncover.
The surprising discovery behind the research
Researchers Professor Steve Dorus and Professor Scott Pitnick at Syracuse University, working with Professor Mariana Wolfner at Cornell University, have been studying what scientists call sperm-female interactions.
Their earlier research produced an intriguing discovery.
Using fruit flies as a research model, the scientists found that sperm undergo important molecular changes after entering the female reproductive tract.
Even more surprisingly, proteins produced by the female begin attaching to and interacting with sperm.
During longer-term sperm storage, the researchers found that female-derived proteins could account for almost 20% of the proteins associated with the sperm.
Why does that matter?
Some of these proteins appear to be involved in the processes cells use to produce energy.
Researchers therefore believe the female reproductive environment could potentially be helping sperm maintain the energy and function they need to survive and ultimately fertilise an egg.
Could this help explain unexplained infertility?
This is where the research becomes particularly interesting for fertility patients.
Anyone who has received a diagnosis of unexplained infertility will understand how frustrating those words can be.
Tests may suggest that:
- ovulation is occurring
- the fallopian tubes appear open
- ovarian reserve is within an expected range
- semen analysis looks normal
Yet pregnancy still doesn’t happen.
“Unexplained” doesn’t necessarily mean there isn’t a biological reason.
It can simply mean that current fertility tests haven’t been able to identify it.
Researchers now want to investigate whether some of the interactions occurring between sperm and the female reproductive environment could eventually help explain fertility problems for which we currently don’t have an answer.
Could sperm that looks healthy still encounter problems?
Potentially – and this is one reason the research is so interesting.
A standard semen analysis can give fertility specialists valuable information about factors such as sperm concentration, movement and shape.
But conception requires much more than sperm simply being present and moving.
Sperm must successfully navigate the reproductive tract, undergo biological changes and become capable of fertilising the egg.
The new research is exploring the molecular conversations taking place during that journey.
Scientists hope that understanding them could eventually reveal fertility problems that today’s tests simply can’t see.
But there’s an important point: this research is not yet in humans
Although the findings are exciting, we need to be careful about what they mean for people trying to conceive today.
The discoveries behind this research were made using Drosophila – fruit flies.
Fruit flies are widely used by scientists because many fundamental biological processes can be studied much more quickly in them.
However, findings in fruit flies cannot simply be assumed to work in exactly the same way in humans.
This is early-stage research designed to help scientists understand the basic biology of reproduction.
It does not currently mean there is a new fertility test or treatment available.
What happens next?
The research team has now received a five-year, $1.6 million grant from the US National Institutes of Health to investigate these sperm-female interactions in greater detail.
One of their goals is to identify which female proteins interact with sperm and understand what those proteins actually do.
Researchers will investigate whether they influence:
Sperm survival – how long sperm remain viable.
Sperm energy – whether the female environment helps provide or regulate the energy sperm need.
Sperm performance – how effectively sperm function after entering the reproductive tract.
Fertilisation – whether these molecular interactions ultimately affect the chance of an egg being fertilised.
If scientists can understand these processes, the findings could eventually give researchers new clues about why conception succeeds for some people and not for others.
Could this lead to new fertility tests?
Possibly – but this is a longer-term possibility rather than something available now.
If similar biological processes are eventually demonstrated to be important in human reproduction, researchers believe the work could potentially help identify causes of infertility that current investigations miss.
In the future, that might mean more detailed fertility diagnostics rather than simply being told:
“Everything looks normal.”
It could also potentially help researchers develop treatments aimed at a specific biological problem instead of using the same approach for everyone.
But considerably more research will be needed before we know whether this can translate into human fertility care.
Why research like this matters
Around 1 in 6 people globally experience infertility, according to the World Health Organization.
Yet despite huge advances in IVF and reproductive medicine, there is still an enormous amount we don’t completely understand about how conception happens.
Fertilisation isn’t simply:
egg + sperm = embryo.
There are countless biological steps and interactions taking place along the way.
And understanding those hidden processes may eventually help scientists answer one of the most difficult questions fertility patients can face:
“Why aren’t we getting pregnant when our tests appear normal?”
For people experiencing unexplained infertility, research like this offers an important reminder.
A diagnosis of “unexplained” doesn’t necessarily mean there is no explanation.
It may mean science hasn’t found it yet.
Trying to understand why you’re not conceiving?
If you’ve been trying to conceive and aren’t sure what your next step should be, Babble Connect by IVFbabble brings together tools, trusted information, fertility clinics and experts to help you better understand your options.
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The aim isn’t to diagnose you online.
It’s to help you become better informed so you can ask the right questions and have more productive conversations with your fertility specialist.
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