Sperm in the first fraction are more numerous, have better motility, and are also found to contain better quality DNA, therefore leading to a much higher chance of fertilization when they come into contact with the egg. Much less DNA fragmentation ie. higher quality DNA, is seen in the first fraction of sperm produced, which is more likely to lead to a healthy pregnancy and birth following fertilization.

http://www.sciencedaily.com/releases/2015/05/150526085347.htm

published research paper:

http://www.tandfonline.com/doi/pdf/10.3109/19396368.2014.999390