A reduction in the quantity of red blood cells per unit volume of blood to below normal levels.


A protein produced by B lymphocytes in response to contact with an antigen from a foreign microorganism and triggered by T lymphocytes. Antibodies attach themselves to the foreign antigen, and to nothing else. This signals other elements of the immune system, including monocytes and macrophages, to destroy the invading organism.


1. Any substance capable of reacting with the products of an immune response, that is, specific antibodies, or sensitized T-lymphocytes or both. 2. An extruding molecule on the surface of a cell, microorganism, toxin or other foreign body which is capable, under appropriate conditions, of inducing a specific immune response when coming into contact with a lymphocyte or antibody.


Absence of living sperm in semen.


Barrier method

A contraceptive method that establishes a physical or chemical barrier between the sperm and ovum, e.g., condom, diaphragm, foam, sponge, cervical cap. Some of the barrier contraceptives are used in conjunction with a spermicidal agent.


The collection of industrial processes that involve the use of biological systems. For some of these industries, the processes involve the use of genetically engineered organisms.



The process by which sperm become capable of penetrating an egg, which occurs in the female reproductive tract.

Cervical cap

Small latex or plastic cap that covers the cervix. Users of this barrier method of birth control must spread spermicidal cream or jelly inside the cap.


A sexually transmitted disease caused by the Hemophilus ducreyi bacterium and characterized by a soft sore on the genitals which becomes painful and discharges pus.

Chlamydia trachomatis

A microorganism that can cause vaginitis, urethritis, cervitis, pelvic inflammatory disease, and lymphogranuloma venereum (LGV). Women with positive chlamydia cultures are more likely to have the following: cervical discharge (yellow or green), erythema, ectopy, friability, and white blood cells on microscopic evaluation of cervical secretions. Also called chlamydia, mucopurulent cervicitis, and nongonococcal urethritis (in men).


Entry or penetration of the penis into the vagina. Also called intercourse or copulation.


A difficult factor or issue often appearing suddenly or unexpectedly.


Generally the beginning of pregnancy. Conception is usually

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement