This Ethernet cable can be a source of RF radiation and so needs to be shielded. There are lots of different qualities of cable category 5, 6, 7 etc. I recommend buying at least Cat 6a SSTP (screened shielded twisted pair) Ethernet cable. Maybe the cable that came with your modem/router is Cat 6a SSTP. In that case you’re OK. If in doubt change it.
And, it’s not just sperm. The results of an animal study suggest that some wireless frequencies may prevent egg implantation. During the study, mice exposed 2 hours a day for 45 days had significantly increased oxidative stress levels. The cellular damage and impact on DNA structure from exposure suggest a strong possibility of abnormal pregnancy or failure of the egg to implant. 
In response, we would state that all wireless frequencies currently used by the public are categorized as radiofrequency radiation. People have not been using Wi-Fi for as long as they have been using cell phones, so the research that has looked at long term use of cell phones is very important in considering the long term health risks from wireless and Wi-Fi specifically.