Study Summary
3 minute readBefore ICSI, the lab has to pick which sperm to inject. The old standard is a swim-up, where the fastest swimmers rise into a layer of fluid and are collected. Newer microfluidic devices let sperm swim through tiny channels instead. The method is designed to select the healthiest ones and handle them more carefully. This study tested one specific device, the SwimCount Harvester®, head to head against the traditional swim-up method.
For each of the 100 couples, the male partner's semen sample was split in two and prepared both ways, and the woman's eggs were split into two groups and injected with sperm from each method, so every couple was their own comparison. The SwimCount Harvester device produced cleaner sperm, with less DNA damage, and more of the eggs it fertilised went on to become usable blastocysts (40.5% versus 34.5%).
- Hypothesis: that a microfluidic sperm-selection device produces better-quality sperm and better embryos than a standard swim-up.
- Study Type: a prospective, double-blind study using sibling eggs, where each couple's sample and eggs are split and prepared both ways. Splitting within the same couple is the strongest design for a question like this, because it removes any differences between couples. It's a lab-outcome study, not a pregnancy study.
- Conclusion: the device gave cleaner sperm (lower DNA fragmentation), more usable blastocysts and better embryo quality, and reached the blastocyst stage faster, than a swim-up. It didn't report whether that turns into more pregnancies or live births.
Compare the two methods
Pick a lab outcome to see the SwimCount Harvester device against the traditional swim-up, from the same couples. The study measured lab outcomes only, not pregnancy or live birth.
The study
This study measured sperm quality and lab embryo outcomes through the blastocyst stage. It did not measure pregnancy or live birth.
Study population
These were couples doing ICSI with reasonably normal sperm, not couples with severe male-factor infertility (which were excluded). So it speaks to how sperm are selected as a routine lab step, not to rescuing the hardest male-factor cases.
Couples doing ICSI who want the sperm-selection step done in a way that lowers DNA damage and, on this data, yields more usable blastocysts. It may matter most where DNA fragmentation is a factor.
Severe male factor was excluded, so this doesn't tell you how the device performs there. And because there's no pregnancy or live-birth data yet, it doesn't prove more babies, only better embryos in the lab.
Methodology
- Each couple's semen sample was divided and prepared two ways, and their eggs were split and injected with sperm from each method, so the two arms come from the same couple at the same time. This sibling-egg design is what makes a small study like this credible.
- Sperm were measured before and after selection for concentration, motility, normal shape, chromatin stability and DNA fragmentation. The embryos were followed through to check usable blastocyst rate, good-quality embryo rate, morphokinetics (how they developed on time-lapse) and an AI score, plus euploidy.
What they found
Cleaner sperm with less DNA damage
The SwimCount Harvester device gave significantly higher sperm concentration, more normally shaped sperm, better chromatin stability and lower DNA fragmentation than the swim-up method. Sperm DNA damage is linked to poorer embryo development and higher miscarriage, so lowering it is an important outcome.
More usable blastocysts and better embryos
The usable blastocyst rate was higher with the SwimCount Harvester (40.5% versus 34.5%), the good-quality blastocyst rate was higher (30.8% versus 23.4%), and embryos reached the blastocyst stage a little faster (106.9 versus 109.5 hours). The gain was clearest in women whose eggs were lower quality: the study graded each egg with an AI tool, and the biggest improvement was in eggs scoring 6 or below. Fertilisation and euploidy rates themselves were no different between the two methods.
What it means for older women
Age isn't only a female challenge. Sperm DNA fragmentation tends to rise with the man's age, and higher DNA damage is linked to poorer embryo development and more miscarriage. On the female side, egg quality and the share of eggs that make a good blastocyst both fall with age. So the stage this device targets, turning fertilised eggs into usable blastocysts, is one that gets harder as both partners get older.
For an older couple, a sperm-selection step that lowers DNA damage and yields more usable blastocysts is an option worth discussing. The limit is that this study stops at the embryo. There hasn't yet been a study showing the extra blastocysts become extra babies.
Evidence strength
The sibling-egg, double-blind design is a real strength and makes the lab findings trustworthy for a study of this size. The weaknesses are that it stops at the embryo, with no clinical outcomes, and that it was funded by a company (Theramex), which is worth knowing even though the funder is stated to have had no role in the analysis. It's strong enough to prefer this specific sperm-selection method. It's the same device category as ZyMot®, but a different design, so it isn't directly comparable to ZyMot.
Things you can discuss with your doctor
- If you're doing ICSI, ask your clinic how they select the sperm, and whether they have or could obtain the SwimCount Harvester microfluidic device. Especially where an older male partner (past 33 to 35) is involved, or if you've had challenges with egg quality.
- Ask about a sperm DNA fragmentation test if it hasn't been done, since that's one of the problems this step is designed to reduce.
- Keep the limit in mind: this improves embryos in the lab and hasn't yet been shown to improve pregnancy or live birth, so weigh it as a low-risk option rather than a guarantee.
Source: Meseguer F, Carrion-Sisternas L, del Arco A, et al. Novel sperm selection device on the basis of microfluidics improves usable blastocyst rates, embryo morphology, and morphokinetic patterns. Fertil Steril Rep, 2025. Funded by Theramex.
Written by
Michelle Bourke
Founder of Better IVF. I went through IVF over 38 myself, and I write these guides to be the clear, properly-sourced resource I wish I'd had, more honest than the forums and deeper than the clinic pages.