Sperm DNA fragmentation in clinical practice.

We value the comments written by Dr. Benagiano on the “Clinical utility of sperm DNA fragmentation testing: practice recommendations based on clinical scenarios” (1). The author has pointed out the controversies surrounding the diagnostic potential of conventional semen parameters and tests of sperm DNA fragmentation (SDF) in cases of recurrent pregnancy loss and in predicting the outcomes of assisted reproductive techniques (ART). He concluded that SDF testing is a useful tool to assess chromatin integrity and understand the origins and mechanisms of DNA damage, however, its clinical utility is somehow hindered by the lack of well-designed studies and therefore is not widely accepted.

Conventional semen analysis is the cornerstone of male fertility evaluation. While it provides useful information on the patency of sperm production, secretions of the accessory organs, as well as ejaculation and emission, it does not predict fertility (2,3). It provides no insights into the functional potential of the spermatozoon to fertilize an ovum or to undergo the subsequent maturation processes required to achieve fertilization. Dr. Benagiano has cited previous studies which showed an association between poor sperm quality and pregnancy outcome (4-7). However, more recent studies have underscored the low diagnostic potential of poor sperm quality in predicting pregnancy outcome whether naturally or through ART. In a retrospective review of 67 patients with severe teratozoospermia (<1% normal forms), Kovac et al. reported natural conception in half the study patients. Moreover, 29% of men with 0% normal forms were still able to conceive (8). Likewise, previous studies reporting a significant influence of sperm morphology on the pregnancy outcome following ART (9) were questioned as some recent studies failed to replicate such an association (10,11). Studies on other semen parameters have yielded similar results too. Lemmens et al. (12) assessed the predictive value of sperm morphology, total progressively motile sperm count, and number of inseminated progressively motile spermatozoa in 4,251 intrauterine insemination cycles. After multivariate analysis, the authors observed that the studied parameters had a low predictive power for pregnancy. The existing drawbacks in the predictive potential of conventional semen analysis triggered the search for other tests that can be utilized in clinical practice (13). SDF testing is a good example of an an ancillary test that can aid clinicians in their efforts to improve patients’ reproductive outcome. In contrast with conventional semen parameters, measures of SDF had better correlation with early embryo development and pregnancy outcomes both naturally and after ART (14,15).

Dr. Benagiano has pointed out earlier studies which detected a relationship between sperm quality and early embryo development suggesting that the sperm may have functions that extend beyond being a DNA delivery vessel. However, it is reasonable to postulate that sperm DNA defects are probably more influential on early embryo development. In fact, several studies have confirmed such an association. Simon et al. (14) evaluated 215 men from infertile couples undergoing ART comparing embryo development between low and high SDF groups. They detected a higher percentage of good quality embryos and a lower percentage of poor quality embryos in the low DNA damage group (P=0.05) compared with the high DNA damage group. Implantation was also inversely related to the degree of SDF in the study population (P=0.001). Wdowiak et al. (15) evaluated the relationship between SDF dynamics, embryo development and pregnancy rate. In 148 couples undergoing ICSI, the SDF level (sperm chromatin dispersion test) was assessed at the day of the microinjection, as well as after 3, 6 and 12 h of incubation. The SDF level and the intensity of fragmentation were correlated with embryo growth and pregnancy outcome. The authors concluded that embryo development up until the moment of obtaining a 5-cell stage and emergence of a blastocyst, depends on the initial SDF, while the chances of pregnancy were dependent on the intensification of SDF after 12 h incubation, where a 1 unit increase in SDF, lowered the chances of pregnancy by 5.95%.

The controversy surrounding the utility of SDF in clinical practice mainly stems from the contradictory results being reported by various studies and meta-analyses, as appropriately described in Dr. Benagiano’s commentary. The author cited a literature review by Lin et al. (16) where they investigated the relationship between SDF (measured with SCSA), high DNA stainability (HDS), and outcomes of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). After reviewing 223 couples, the authors failed to detect significant differences in IVF and ICSI fertilization rate, good embryo rate, and pregnancy rate between various levels of SDF or HDS. Moreover, higher SDF was not associated with a significant increase in abortion rate post IVF. Contrary to this, the systemic reviews and meta-analyses [reviewed by Agarwal et al. (1,17)] showed significant negative association between SDF levels and pregnancy rates with IVF (18,19), and a significant positive association between SDF levels and miscarriage rate after IVF and ICSI (18,20,21). Such controversies are expected in medical literature and are mainly caused by the variation in study methodologies, selection criteria, and particularly in this case, the SDF testing method being utilized. Although the American Society for Reproductive Medicine has recommended against routinely using SDF testing for the evaluation of male fertility, however, they did acknowledge the presence of a potential influence for SDF on pregnancy outcome after ART; as stated in their committee opinion (22) “…but the effect of abnormal sperm DNA fragmentation on the value of IUI or IVF and ICSI results may be clinically informative”.

In clinical practice, it is perhaps more meaningful to look at the broader picture. SDF is not being compared to a gold standard test with superior or even equivalent clinical usefulness, in fact such a test does not exist. So from a patient and physician perspective, any test that can offers valuable information influencing the reproductive outcome deserves to be taken into consideration. It should be understood that we are not proposing the routine use of SDF during the fertility evaluation of every infertile man. Instead, we believe that in selected clinical scenarios, SDF provides beneficial information that can affect clinical decision making and consequently reproductive outcome.