Usually one can definately try IUI before IVF.But after 30 years of age better to go for IVF directly and not to waste cycles for IUI. IUI near natural process.Good quality of sperms are filtered out and then injected in uterus.After that they take natural course to fertilise egg.But IVF is more controlled and advanced process in which natural course is further reduced by fertilising egg outside body and confirming that èmbryo has formed.So woman come one more step closure to become pregnant .Other advanced IVF procedure also reduce some other natural factors.But last and most important natural factor that is acceptance of embryo by mother's uterus still depends on nature which no one can predict or assure.