Non-obstructive azoospermia Spermiation failure 2023-07-01T12:16:07Z Spermiation failure is indicated by apparently normal spermiogenesis, but the presence of retained Sd2 spermatids in stages III-V of human spermatogenesis, whereas maturation arrest is indicated by a lack of late Sd1 and Sd2 spermatids in the epithelium. It is important to note that multiple spermatogenic abnormalities often occur simultaneously in infertile men, and the helical nature of human spermatogenesis can make it difficult to readily discriminate multiple abnormalities of spermatid development and release.