In a 2025 study, the sperm selection device Zymot modestly improved blastocyst development compared with conventional sperm processing method (density gradient centrifugation) in donor egg cycles using frozen sperm, though fertilization rates were similar.
Sperm preparation is a key step in IVF or ICSI, with density gradient centrifugation being a standard method. This is where viable sperm are separated from dead sperm by spinning (centrifugation).
Another method is microfluidics, where semen is injected into a device and motile sperm travel through a chamber to be collected for insemination. These devices have been shown to select sperm with lower sperm DNA fragmentation (SDF), and have been linked to improved fertilization. A popular microfluidics device is Zymot.
Since Zymot only allows select sperm to pass through the device, the concentration of recovered sperm is typically low. For this reason, embryologists may be cautious when using Zymot with frozen sperm, especially if the sample already has a low concentration.
A study by Gavriil et al. (2025) investigated whether Zymot improves fertilization or embryo development compared with density gradient centrifugation, using sibling donor oocytes and frozen sperm (donor eggs were split). This study was done in the general population and not in men with high sperm DNA fragmentation.
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Study details
- Study type: Prospective study that took place at a single IVF center in Greece.
- Participants: 150 couples undergoing donor oocyte ICSI cycles. Each couple received ≥8 mature donor eggs that were split into two groups depending on how the sperm was processed: either by density gradient centrifugation or by Zymot (150 patients for each method). Sperm was collected in advance, frozen, and thawed on the day of egg retrieval. Embryologists were blinded to which method was used.
- Study inclusions/exclusions: Men with azoospermia, very low motility (<1 million/ml), or cryptorchidism (absence of a testicle) were excluded. Donors were 18–35 years old, healthy, and screened per Greek law. A minimum of 1.5 million progressively motile sperm was required.
- Key outcomes: Fertilization, cleavage, total blastocyst formation, top-quality blastocyst formation (embryos with expansion 2-6 that were graded as either AB, AA or BA).
- Potential conflict of interest: This study received partial funding from Zymot (free test kits).
How semen parameters changed after Zymot with frozen sperm
The researchers compared semen parameters from fresh ejaculates with those obtained after thawing and processing using density gradient centrifugation or Zymot.
- Concentration: Fresh samples started high at 43.4 million/ml, dropped after thawing and processing with density gradient centrifugation to 16.3 million/ml, and were lowest with Zymot at 1.0 million/ml.
- Progressive motility: Fresh sperm showed 45.8% motility, which fell after thawing with density gradient centrifugation to 21.5%, but increased sharply with Zymot to 81.5%. This shows that Zymot can greatly enrich for motile sperm in a sample.
- Morphology: Normal sperm were 3.9% in fresh samples, slightly lower after density gradient centrifugation at 3.4%, and improved with Zymot to 4.8%.
This shows that Zymot improved motility and morphology compared with density gradient centrifugation, but at the cost of drastically reducing the final sperm concentration. This happens because the device only allows a small number of sperm to pass through, so concentration drops sharply.
If sperm is to be used for ICSI, a lower concentration isn’t really a problem since you only need a small number to do the procedure. In this study, there were 33 samples that couldn’t have sperm parameters evaluated after Zymot (like motility, morphology, etc.), but there was still enough to perform ICSI. However, this approach would not be suitable for conventional IVF, which requires larger numbers of sperm.
Embryology outcomes following Zymot processing of frozen sperm
They also measured embryology outcomes after using sperm from density gradient centrifugation vs Zymot. They found:
- No difference in fertilization rate.
- No difference in cleavage embryo formation rate.
- An increase in blastocyst formation rate with Zymot (74.0% vs 67.9%, p= 0.016).
- An increase in top-quality blastocyst formation rate with Zymot (66.4% vs 61.0%, p= 0.035)
These results were based off of all the patients. When they split the patients into those with normal sperm (113 patients) and those with abnormal sperm (32 patients), they only found significant differences in the patients with normal sperm.
Conclusion
In this study, Zymot produced significantly higher blastocyst and top-quality blastocyst formation rates compared with density gradient centrifugation. These increases were modest and mainly in men with normal sperm.
Fertilization and cleavage embryo formation rates were similar.
Embryologists may be cautious about using Zymot with frozen sperm, since it drastically reduces sperm concentration, but this study showed it was not a problem for ICSI.
This study included donor eggs to help control for egg quality, so we can more clearly see any effect that Zymot had on sperm quality. However, these eggs are generally higher quality and have stronger DNA repair mechanisms, so donor eggs might mask any negative effects from sperm compared to patients from the general population.
Importantly, this study only used frozen sperm, so the results may not apply to fresh cycles. Studies with fresh sperm have shown mixed results, and overall research in this area is still limited.
I recently reviewed a randomized controlled trial involving fresh sperm and sibling eggs (where a patient’s eggs were split to receive either density gradient centrifugation or Zymot). They found:
- An increase in fertilization with Zymot (76.0% vs 69.9%).
- No difference in high quality blastocyst formation rate or the number of blastocysts frozen.
- No differences in euploid rates.
- No differences in clinical pregnancy or live birth rates.
However, this study also looked at the general population and didn’t look at patients with high sperm DNA fragmentation. More work is definitely needed in this area!
Limitations: Lack of sperm DNA fragmentation data, small subgroup of patients with abnormal sperm, no power calculation to ensure the sample size was large enough, and no pregnancy outcomes reported.
Related studies
These additional studies were referenced by the authors of the paper and haven’t been covered on Remembryo. They may be helpful if you’re exploring this topic further. This section is available for paid subscribers.
Reference
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About Embryoman
Embryoman (Sean Lauber) is a former embryologist and the founder of Remembryo, an IVF research and fertility education website. After working in an IVF lab in the US, he returned to Canada and now focuses on making fertility research more accessible. He holds a Master’s in Immunology and launched Remembryo in 2018 to help patients and professionals make sense of IVF research. Sean shares weekly study updates on Facebook, Instagram, and Reddit regularly. He also answers questions on Reddit or in his private Facebook group.
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