A - B - C - D - E - F - G - H - I - K - L - M - N - O - P - Q - R - S - T - U - V - X - Y - Z Necrospermia - Condition in which sperm are produced but are found dead in the semen and are unable to fertilize eggs. NEST - See Nonsurgical Embryonic Selective Thinning. Nonsurgical Embryonic Selective Thinning - A form of assisted hatching using a chemical to thin the outer membrane of the zona pellucida rather than scraping. Non-surgical Sperm Aspiration - The procedure is performed under sedation. A tiny needle is used to extract sperm directly from the testis in those who have blocked ducts or cannot ejaculated. Used in conjunction with in vitro fertilization and ICSI. NSA - see Nonsurgical Sperm Aspiration.