I'm having trouble finding helpful information pertaining to my husband's sperm quality/quantity due to his diabetes. In what ways can his diabetes affect his fertility?

He struggled with some ED issues at one point, but everything seems to be in ship shape now. Over the last few years he's tried hard to keep his levels in control (he was bad about managing it for a long time.) He is relatively healthy at this point, and his sugars have been mostly in range. I just want to know if it affects his sperm in any way. Thanks!