If you are a couple presenting for infertility evaluation and you have not been able to achieve a pregnancy for a year or more, and you have, on average, over twice as many sperm with DNA fragmentation than the average fertile couple, you may need to be investigated for abnormal DNA fragmentation levels.
Also, couples experiencing infertility or miscarriage are more likely to have a male partner with moderate or high levels of DNA fragmentation.
But you may ask what is sperm DNA fragmentation, what causes it and how is it related to other semen parameters or affect male fertility?
The genetic health of sperm is important. It is solely to carry genetic material (DNA) from the man and combine with the genetic material contained within the egg of the mother, creating a unique genetic code for the baby.
Since DNA carries all of the instructions for the development of an embryo, it makes sense that the genetic integrity of sperm is a key consideration in fertility. Any damage to the DNA within sperm may interfere with the sperm’s ability to properly fertilize an egg or develop into a healthy, thriving embryo. This is exactly the issue with sperm DNA fragmentation.
Interestingly, sperm DNA fragmentation is less often tested—and generally less well understood—than other semen parameters and sperm quality measures, such as sperm count, motility, and morphology.
But as the relationship between sperm DNA fragmentation and birth rates is further established, there’s an emerging realization that sperm genetic integrity is one of the most important factors for male fertility.
In order to understand what sperm DNA fragmentation is all about, the basics of the proper structure of DNA should be appreciated.
In an age when a small amount of high-quality sperm can lead to pregnancy through in vitro fertilization (IVF), the integrity of genetic material in sperm is essential for successful fertilization and normal embryo development.
Sperm DNA fragmentation is a term used to identify abnormal genetic material within the sperm, which may lead to male subfertility, IVF failure, and miscarriage.
Healthy DNA is distinguished by a double-helix spiral held together by cross-bonds that together appear to form the shape of a ladder. However, when any of the DNA “rungs” become broken or unstable, the whole genetic ladder becomes unsteady. This results in sperm fragmentation that can lead to chromosomal abnormalities, which can contribute to birth defects.
Not only does DNA fragmentation directly correlate to lower fertility in men, but it is also linked to recurrent pregnancy loss (two or more failed pregnancies).
Be aware that DNA is packaged into structures called chromosomes. While most cells within the human body contain 46 chromosomes, sex cells or “gametes” (eggs and sperm) contain just 23. When they combine, they create a full organism with the proper number of chromosomes.
You may not know it, but DNA damage is actually quite common in the human body, luckily most cells have the ability to identify and correct damage to their own genetic code. While immature sperm that are still in progress may have the ability to repair their own DNA to some extent, mature sperm do not.
Eggs can actually somewhat compensate for this, and upon fertilization, have their own processes to repair errors in sperm DNA. But if the damage is too extensive—or if the egg is less able to perform this repair, possibly due to age—the damage can endure to the embryo stage. The result may be the embryo’s failure to develop or implant (infertility), miscarriage (possibly recurring), or genetic abnormalities or illness within the offspring.
The DNA fragmentation index, or DFI, refers to the percentage of sperm in a particular semen sample with fragmented DNA. A higher DFI means that a larger percentage of a man’s sperm contains genetic damage.
Generally, a DFI over 30–50 percent is considered high, and may impact fertility.
In some cases, subfertility may be experienced even among those with a DFI of 15–30 percent, especially if other abnormal semen parameters are present (such as low sperm count or poor motility or morphology), or the female partner is older, as older eggs are less able to correct the damaged DNA within sperm.
If you are having high levels of sperm DNA fragmentation, you are also more likely to have other abnormal semen parameters, such as poor sperm motility or morphology. Generally the average level of DNA damage is significantly higher among those with other abnormal semen parameters. Higher sperm DNA damage is correlated with poorer semen parameters (sperm concentration, motility, morphology).
Having abnormal results in all three categories equates to higher levels of DNA fragmentation than for those with normal semen parameters.
In infertile men with isolated sperm defects (such as poor motility, poor morphology, or low sperm count, and not a combination) the levels of sperm DNA fragmentation are significantly higher than in men with poor sperm motility.
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 earlier, abnormal semen parameters can compound sperm DNA fragmentation issues. However, high sperm DNA fragmentation can impact fertility even when not paired with other factors.
If you are having a high rate of sperm DNA fragmentation, you are at an increased risk for infertility, but conception is absolutely possible for you and you can achieve full-term pregnancy with your spouse or partner.
Many couples unable to achieve pregnancy tend to have an average of sperm with DNA fragmentation significantly higher than couples that achieve pregnancy. This is one reason why DNA fragmentation can be a predictor of the outcome of assisted reproductive technology ART) procedure.
While it’s not entirely clear that sperm DNA fragmentation causes recurrent pregnancy loss (defined as two or more consecutive miscarriages), the two issues are correlated. The genetic integrity of sperm is a significant predictor for future miscarriage and infertility.
It is well accepted that sperm fragmentation leads to complications, including miscarriage and infertility. Rather than wait for a definitive test, it stands to reason that you should take steps that can reduce the effects of DNA fragmentation.
In addition to tests, curtail or eliminate negative behavioral habits, such as smoking, drinking, and exposure to toxins and pollutants.
There’s really no time that’s too early for testing. Especially because sperm DNA fragmentation may be treatable with lifestyle interventions, testing earlier in the fertility process can ultimately save time, energy, and money, and prevent you from undergoing more invasive procedures.