After being diagnosed with "unknown infertility" probably due to maternal age (38 at the begining of treatment) I went through 1 cycle of Chlomid and 3 IUI's with Follistin and Femara without success.  After that, we took out the big guns and had an IVF done.  Only then did we find out my eggs had coarse zona pellucidas (their outer cover), which don't allow sperms to naturally break the egg open.  Assisted hatching and ICSI were done but eventhough 3 pre-embryos formed, none transformed into pregnancies.  After that we decided to change to a better known and experienced reproductive endocrynologist and he decided there were too many loose ends in my treatment.  One being a laparoscopy since his experience told him that women with coarse zona pellucida also have endometriosis (he said this has not been written in the literature yet).  I had a laparoscopy and hysteroscopy done one week ago (at age 40) and there it was:  endometriosis at six different spots.  Also, I had a polyp, my right Fallopian tube had two "free fingers" and three attached to one another, and my left ovary was kind of stuck to my other Fallopian Tube.  All that was corrected and now I'm waiting to start a fresh new cycle with Femara and feeling very optimistic about it.  I know I have better odds of pregnancy now.  Just want to let everybody know that "unknown infertility" does not exist.  It just happens that the cause has not been found yet.