Sperm morphology's effects on fertility. While the most common cause of male infertility is low sperm count, the shape of the sperm can also play a role. Morphology can affect fertility because sperm need a certain shape to be able to penetrate the outer layers of the egg. Aug 15, - You want at least 4% of sperm to be a normal shape. Otherwise, you could have fertility problems because of abnormal sperm morphology.