The overlooked half of the picture
When a couple starts fertility investigations, the default sequence is almost always the same: bloods and a scan for her, a semen analysis added as a secondary step. It's a pattern that reflects decades of reproductive medicine being built almost entirely around female biology — and it has a real cost. Sperm factors are identified as a primary or contributing cause in around half of all fertility challenges, yet they're routinely under-investigated until everything else has been ruled out.
A semen analysis, when it finally happens, is often presented as either normal or abnormal — passing or failing. But sperm health is considerably more nuanced than that. A man can have a completely normal semen analysis and still have sperm that is significantly compromising the chances of conception or a healthy pregnancy. The reasons why are only visible through more detailed testing.
A normal semen analysis result doesn't mean sperm health isn't a factor. It means the basic parameters look fine. Those are different things.
What sperm tests actually measure
Most people who've had a semen analysis will have received results for the three standard parameters. Understanding what each one means — and what it doesn't — is the starting point for understanding why additional testing sometimes matters.
| Parameter | What it measures | Normal range (WHO) | What it misses |
|---|---|---|---|
| Count | Number of sperm per millilitre of ejaculate | ≥16 million/ml | Quality of individual sperm |
| Motility | Percentage of sperm that are moving, and how well | ≥42% total motility | Whether moving sperm carry intact DNA |
| Morphology | Percentage of sperm with normal shape | ≥4% normal forms | Genetic integrity of normal-looking sperm |
| DNA fragmentation | Damage to the DNA within the sperm head | <15% DFI (ideal) | Not included in standard analysis |
The gap in that last row matters. Standard analysis tells you how many sperm there are, how they move, and what they look like. It doesn't tell you anything about the genetic material they're carrying. Two men with identical semen analyses can have very different fertility outcomes — because one may have high levels of DNA fragmentation that the standard test simply doesn't measure.
DNA fragmentation — what it is and why it matters
DNA fragmentation refers to breaks and damage in the genetic material inside sperm. Some level of fragmentation is normal. High levels — generally above 25% on a DNA fragmentation index (DFI) test — are associated with lower fertilisation rates, poorer embryo development, higher rates of early pregnancy loss, and, in some research, lower IVF success rates overall.
What makes this particularly important is that high DNA fragmentation can exist in men with completely normal standard semen analysis results. Someone can have a good count, good motility, normal morphology — and still have sperm that is significantly damaged at the genetic level. The only way to know is to test for it specifically.
DNA fragmentation testing is not yet routinely offered on the NHS, but it is available privately — usually through a fertility clinic or a specialist andrology service. The test is called a DNA Fragmentation Index (DFI) or Sperm DNA Integrity Test. Results are typically reported as a percentage: below 15% is considered low risk; 15–25% moderate; above 25% high.
DNA fragmentation testing is particularly worth discussing if there have been recurrent miscarriages, multiple failed IVF cycles, or consistently poor embryo quality — especially where female factors have already been investigated and don't fully explain the outcome. It's also worth considering earlier rather than later, as a high result opens the door to techniques that can work around it.
Techniques that work around sperm challenges
Once sperm quality issues are identified — whether through standard parameters or more detailed testing — there are several techniques that can improve the chances of fertilisation and successful embryo development. They sit on a spectrum from standard to highly specialised.
ICSI is the most widely used technique for male factor infertility. Instead of placing sperm and eggs together and allowing fertilisation to happen naturally, a single sperm is selected by an embryologist and injected directly into each mature egg using a fine glass needle.
It's recommended when sperm count or motility is low, morphology is poor, or when previous IVF cycles have had unexpectedly poor fertilisation. The stimulation and egg collection process is identical to standard IVF — only what happens in the lab differs. ICSI is offered by virtually all fertility clinics in the UK and is often included in standard IVF packages for couples with a known sperm factor.
Limitation: ICSI still relies on the embryologist's visual assessment to select sperm. It doesn't specifically select for DNA integrity — a visually normal sperm can still carry high fragmentation.
ZyMōt is a microfluidic sperm selection device — a small chip through which sperm swim to reach a collection chamber. Only motile, morphologically normal sperm can navigate the device, and crucially, sperm selected by ZyMōt have significantly lower DNA fragmentation rates than those prepared by conventional centrifugation methods.
Conventional sperm preparation involves centrifuging the sample, which creates oxidative stress and can actually increase DNA damage. ZyMōt avoids this entirely — sperm select themselves by their own motility, in a process that closely mimics the natural environment of the female reproductive tract.
It's particularly recommended for men with elevated DNA fragmentation, recurrent failed IVF cycles with poor embryo quality, or recurrent miscarriage where a sperm DNA component is suspected. Not all clinics offer it — it's worth asking specifically.
IMSI uses a very high-powered microscope — up to 6,000x magnification versus the 400x used in standard ICSI — to examine sperm in extremely fine detail before selection. This allows embryologists to identify and exclude sperm with subtle structural abnormalities in the head, which are associated with higher DNA fragmentation and poorer embryo outcomes.
The evidence on IMSI is mixed — some studies show improved pregnancy rates in men with severely abnormal morphology or high fragmentation, while others show little benefit over standard ICSI. It is time-intensive and not widely available. It's most commonly discussed for couples who have had multiple failed ICSI cycles with poor embryo development, where morphology is a known factor.
Important: there is currently insufficient large-scale clinical evidence for IMSI to be formally recommended by bodies such as NICE or the HFEA. Individual clinics may hold anecdotal or internal data that informs their recommendation — if your clinic suggests it, ask them directly what their own outcomes data shows. That conversation is worth having before deciding.
PICSI selects sperm based on their ability to bind to hyaluronan — a naturally occurring substance found in the egg's protective layer. Mature, genetically normal sperm have receptors that allow them to bind to hyaluronan; immature or DNA-damaged sperm typically do not. The test uses a dish coated with hyaluronan to identify and select sperm that demonstrate this binding ability.
The theory is that sperm selected this way are more likely to be genetically intact. A large UK clinical trial (HA-IVF) found modest improvements in miscarriage rates but not in live birth rates overall, though results were more positive in specific subgroups with high fragmentation. Like ZyMōt and IMSI, PICSI is most discussed in the context of previous cycle failures or elevated fragmentation.
Important: PICSI is not currently recommended as a routine add-on by NICE or the HFEA, as the broader evidence base does not yet support a clear benefit for most patients. Some clinics do recommend it based on their own clinical experience and patient outcomes — if yours does, ask to understand what their data shows and which patient profiles they've found it most useful for. That context can help you make a more informed decision about whether it's right for your situation.
What you can actually do
Sperm takes around 74 days to fully develop — which means that changes made today won't be reflected in a semen analysis for two to three months. That window is both a challenge and an opportunity: it takes time, but it also means there is meaningful scope to improve sperm quality before a cycle starts.
The part that doesn't get talked about
Male fertility is discussed clinically and logistically — semen analysis booked, results delivered, treatment adjusted. What's rarely acknowledged is how those results land. For many men, a diagnosis of male factor infertility comes as a profound shock — a challenge to identity, to a sense of self, to the role they expected to play in the process of building a family.
Partners going through IVF are often acutely aware that the physical burden of treatment falls almost entirely on one person. That asymmetry can be its own kind of difficulty — a feeling of helplessness, or of being on the periphery of something enormous that is happening to someone you love.
The investigations, the test results, the techniques — all of that is manageable. What's harder is finding a way to stay connected through a process that can feel isolating for both people, in different ways.
Being the person whose results prompted a change in treatment plan is a specific kind of weight to carry. It deserves to be named, not managed around.