Research demonstrates that men who have high levels of sperm DNA fragmentation are also more likely to have other abnormal semen parameters, such as poor sperm motility or morphology. In one 2002 study of 88 infertile men, researchers found that the average level of DNA damage was significantly higher among those with other abnormal semen parameters. This was confirmed in a 2009 study, in which higher sperm DNA damage was correlated with poorer semen parameters (sperm concentration, motility, morphology). Patients with abnormal results in all three categories had higher levels of DNA fragmentation and were more likely to have high DFI (over 30%) than patients with normal semen parameters.
This can be seen even in studies of those with just one problem with their sperm. In a 2014 study of 196 semen samples, it was found that men with teratozoospermia—a high level of abnormally shaped sperm—had higher DFI than men with normal sperm morphology. That same year, another study of over a thousand infertile men with isolated sperm defects (meaning just poor motility, poor morphology, or low sperm count, and not a combination of the above) found that levels of sperm DNA fragmentation were significantly higher among men with poor sperm motility. Approximately 31% of those men had high sperm DNA fragmentation, defined in this study as over 30% DFI.
Why does this happen? It’s probable that the same underlying factors that contribute to abnormal semen parameters, such as advanced paternal age, smoking, or toxin exposure, also cause high levels of sperm DNA fragmentation. There may be other connections or mechanisms connecting these measures, as well.
This is important to understand because, as stated above, abnormal semen parameters can compound sperm DNA fragmentation issues. However, as we’ll explore below, high sperm DNA fragmentation can impact fertility even when not paired with other factors.
First, a note: conception is absolutely possible for men with sperm DNA fragmentation. Even in studies that report lower pregnancy rates, longer time to conception, or higher miscarriage rates among men with a high DNA fragmentation index, researchers note that full-term pregnancies have been achieved.
That being said, studies demonstrate that men with high rates of sperm DNA fragmentation are at an increased risk for infertility. In one study, men presenting for infertility evaluation—who had not been able to achieve a pregnancy for a year or more—had, on average, over twice as many sperm with DNA fragmentation than fertile men (27.6% vs. 13.3%). In another, couples experiencing infertility or miscarriage were more likely to have a male partner with moderate or high levels of DNA fragmentation; researchers concluded that “spermatozoa with denatured DNA… were the best predictor for whether a couple would not achieve pregnancy.”
This trend—higher levels of DNA fragmentation within sperm correlating with lower live birth rates—holds true even for those being treated for infertility with in vitro fertilization (IVF). In one study of 360 couples undergoing IVF, higher sperm DNA fragmentation levels were associated with lower fertilization rates, embryo quality, and pregnancy rates. The couples who were not able to achieve pregnancy had an average of 51.7% sperm with DNA fragmentation, as opposed to 39.5% in the pregnant couples. The researchers concluded that DNA fragmentation “can predict ART [assisted reproductive technology] outcome.”
This study was especially valuable because, other than DNA fragmentation results, there were few significant differences between the group that achieved clinical pregnancy and the group that didn’t. The sperm count, motility, semen volume, and other parameters were all basically equivalent between the two study groups. This allows us to surmise that DNA fragmentation impacts fertility independently of other semen parameters.