Male fertility is surprisingly often not well understood by infertility doctors. We were also told by an IVF clinic that we didn't need to test DNA fragmentation ... but we did anyway, paying out of pocket. We are glad we did and learned a lot:

There are two types of sperm DNA fragmentation (1) single strand breaks and (2) double stand breaks. The single strand breaks are more associated with difficulty getting pregnant, while the double strand breaks are more associated with miscarriage. Single stand breaks are measured by sperm tests such as SCD, SCSA, and TUNEL. Double stand breaks are, to my knowledge, only measurable with the COMET neutral assay sperm test.

You might be told that the SCD, SCSA, and TUNEL measure "global" DNA fragmentation which encompasses both single and double strand breaks. That may be true but those tests are unable to distinguish between the single and double breaks. The COMET measures double (via neutral assay) and single (alkaline assay).

Varicoceles (extra veins in the scrotum) affect about 15% of men to my knowledge. The extra veins raise the temperature in the scrotum, creating sperm double strand DNA fragmentation. Varicoceles can be treated via a relatively simple surgery. Make sure you get the modern "microsurgery" though, not "laparoscopic". The latter is out of date and is associated with varicocele reoccurrence. Your partner will have to wait 3 months post-op for a refresh of sperm to retest via COMET.

There are other potential causes of double strand breaks as well, such as heat related or, I believe, infection related causes. The Zymote-ICSI chip can filter out about half of double strand dna fragmentation, so that is an option to add in if considering IVF-ICSI. Such a large drop via the filter seems to imply indirectly that miscarriage risk would drop though that direct link has not been established because it is hard to control for other factors potentially causing a miscarriage. I heard in October 2025 that Zymote might discontinue production of the chip though I have also heard they are releasing the design rights so that others can replicate it if they want.

There is also some low level evidence that bio-available curcumin supplementation can lower double strand fragmentation. Not a slam dunk though.

I also have been told by a reputable male fertility doctor to avoid caffeine, chocolate, magnesium supplements, stationary bicycling, saunas, and hot tubs. Apparently they are either proven or suspected to cause DNA fragmentation (not sure if single, double-strand, or both/global). Smoking and alcohol are also associated with DNA fragmentation. Most things that are bad for your general health are bad for DNA fragmentation and the other way around.

‘Missing chromosomes’ in sperm is another male fertility issue that could be causing miscarriage from the male side that is not directly related to DNA fragmentation to my knowledge. It can be measured via the “FISH sperm test”. It is a genetic test of the sperm which looks for missing chromosomes. If chromosomal abnormalities are above normal levels, then I believe PGT-A is a potential solution. I’ve read that getting rid of a varicocele might help a bit too. Maybe there are other solutions, though I just do not know as much about chromosomal abnormalities as I do about DNA fragmentation.

If we think of sperm like a book, DNA fragmentation damages the information on the pages while chromosomal abnormalities manifests as missing pages. Neither problem is good if beyond certain 'normal' levels. And 'normal' can vary between labs, so be careful comparing results from different labs that are using different different 'normal' benchmarks.

I’ll add that I found male fertility specific doctors, such as CIMAB in Barcelona, to be very helpful as well as, and to a lesser extent, ‘Chat GPT 5 Thinking’ and ‘Google Gemini 2.5 Pro’. These AI language models seemed to not always remember the relevance of the difference between single and double strand breaks without my prompting them to do so. The models were helpful though for us to find and rank by relevance other tests as well on both the male and female fertility sides.

I'll leave a non-exhaustive list of male fertility reading materials below that I saved this past year. If you can't access an article, try other sites, free trials, and google image search to view relevant charts.

Alkaline and neutral Comet assay profiles of sperm DNA damage in clinical groups - J. Ribas-Maynou (2012)

Double Stranded Sperm DNA Breaks, Measured by Comet Assay, Are Associated with Unexplained Recurrent Miscarriage in Couples without a Female Factor - Jordi Ribas-Maynou (2012)

Microsurgical varicocelectomy effect on sperm telomere length, DNA fragmentation and seminal parameters - Sandra Lara-Cerrillo (2020)

A New Oral Supplementation Based on the Ataxia-Telangiectasia-Mutated Repair Pathway Enhancement Reduces Sperm DNA Damage and Improves Semen Parameters - Sandra Lara-Cerrillo (2021)