Unexplained infertility is that infertility cause is remaining unknown even after the all checkup of infertility. Doctor will prescribe all tests like semen analysis to known male factor, ultrasound, and blood test to female. But all these test reports are normal and the reason of infertility is still unsuspected. So, this is called unexplained infertility.
Unexplained infertility abnormalities are likely to be present but not detected by recent methods. Possible problems could be that the egg is not released at right time of fertilization that it may not enter the fallopian tube, sperm may not be able to reach the egg, fertilization may fail to occur, transport of zygote may be disturbed, or implantation fails. It is increasingly recognized that egg quality is of critical importance and women of advance maternal age have eggs of reduced capacity for normal and successful fertilization.
Reproductive immunology such as decreased maternal immune tolerance towards the embryo may also be possible explanation. However, a growing body of evidence suggests that epigenetic modifications in sperm may be partially responsible.