Some of the more common causes of infertility are diminished ovarian reserve (older women or women with premature ovarian failure), blocked fallopian tubes (sometimes because of endometriosis, pelvic inflammatory disease, and STDs), endometriosis and polycystic ovarian disease. Low sperm count, poor sperm morphology (the shape of the sperm) and poor motility (the ability of the sperm to swim in the right direction) are also major contributors to a couple's infertility. The estimates are that overall fertility problems are 50 percent female and 50 percent male.