Testing sperm for male/female ratios prior to ttc?

Before we try and conceive again (this would be our fourth and final), DH first wants to get his sperm tested to see if he even "makes boys" (we have three girls). I have no idea if this is something that can be done, thought I'd ask on here and see if anyone has done this or previously looked into it. Thanks!

 I'd definitely like to know! We have 4 sons and my DH doesn't think he "makes girls", lol! 

I found this post by tamara regarding this question ' it is not possible to have more of one sperm than the other. X and Ysperm both come from one cell that splits. So for there to be more x sperm than Yhalf of that cell would need to die. For this to happen your dh would have a genetic defect that you would have known about long before now (this defect effects other things besides x and y sperm)' Hope this helps and can persuade your DH's that it is possible to have a different gender!x