Abnormal sperm mid-piece morphology Asymmetrical insertion of the midpiece into the head 2023-07-15T11:53:53Z Asymmetrical insertion of sperm neck Insertion of the neck and midpiece into the head of a spermatozoon on an axis that diverges from the midline axis of the spermatozoon head. This term applies if the proportion of spermatozoa with this defect is above the upper limit of normal.