The International Council on Infertility Information Dissemination, Inc

Natural Killer Cells (NK, CD56+) -- large granular lymphocytes that bond to cells and lyse (causing dissolution) them by releasing cytotoxins. NK cells are known to be effective against cells infected with viruses and some types of tumor cells. When activated, NK cells function to fight, kill and destroy their targets and their excessive numbers in blood is correlated with pregnancy loss and reduced success in IVF cycle outcome.Proliferation of NK cells is produced by gamma interferon, interleukin-2, antibodies, retinoic acid, and prostoglandin-E. It is thought that NK cells may produce TNF (Tumor Necrosis Factor)

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.

Non-obstructive Azoospermia -- Severely impaired or non-existent sperm production. See Azoospermia.

Non-stimulated Oocyte Retrieval In (office) Fertilization (NORIF) -- No ovulation induction hormones are used for this process (unlike SCORIF). The egg is removed by ultrasound aspiration from the ovaries. This procedure is done in the doctor's office. The egg is mixed with sperm and placed in a small plastic dish and left in the incubator for 2 days. The fertilized egg is then transferred to the uterus through a small plastic catheter.

Nonsurgical Embryonic Selective Thinning (NEST) -- A form of assisted hatching using a chemical to thin the outer membrane of the zona pellucida rather than scraping.

Non-surgical Sperm Aspiration (NSA) -- 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.

NORIF -- See Non-stimulated Oocyte Retrieval In (office) Fertilization.

NSA -- see Nonsurgical Sperm Aspiration.