Super sperm could be the primary cause for the inability to conceive.
"Super sperm" is the term used to describe the one sperm that manages to
survive its path to the waiting egg.
Dr. Oren Hasson, Tel Aviv University Zoology Department, believes there is a link between the evolution of the body and infertility. According to the doctor, "super sperm" could be the primary cause for the inability to conceive.
"Super sperm" is the term used to describe the one sperm that manages to survive its path to the waiting egg. These sperm have to be healthy, fast swimmers in order to combat the natural defenses the female body has waiting. In terms of evolution, the male body may be trying to combat the female's defense by overproducing these "super sperm."
The theory, according to Dr. Hasson, works in the same way as an arms race. The male reproductive system has "learned" that only "super sperm" make it to the egg, so it produces more of these agile athletes. The trouble is, after one sperm fertilizes the egg, it can take minutes for the protective barrier to form around the egg preventing any additional sperm from entering. During this time, if another "super sperm" enters the egg, the pregnancy will often be self aborted.
The doctor believes that infertility treatments could combat this effect by carefully placing only a small number of sperm near the egg during in vitro fertilization attempts. When the doctor controls the number of sperm located near the egg, they also control the potential for two or more "super sperms" fighting to fertilize.
Source: Biological Reviews - September 2009