Hey, I'm a pharmacist. As far as I'm aware gabapentin is ok. Very few drugs have a known impact on sperm and so carry the 'don't get anyone pregnant' warning.
The risk is with longer term exposure through pregnancy. All anti-epileptics cause a higher chance of neural tube defects, so women taking them are advised to take a higher dose of 5mg folic acid. And there's little evidence of safety of most medications during pregnancy, because we can't exactly test them, so there's a risk of other problems, but if you need the meds then you need the meds.