n.
Inability of a couple to conceive and reproduce.
It is defined as failure to conceive after one year of regular intercourse without contraception . Inability to conceive when desired can result from a defect at any of the stages required for fertility (see reproductive system ). About one in every eight couples is infertile. Most cases involve the female partner, 3040% involve the male, and 10% are caused by unknown factors. In women, causes include ovulation or hormone problems, fallopian-tube disorders, and a chemical balance that is hostile to sperm ; in men, causes include impotence , low sperm count, and sperm abnormalities. Either partner can have a blockage of the pathways the sperm must travel, often treatable by surgery. Emotional factors may contribute; return of normal fertility may require only counseling. Fertility drugs can stimulate the release of egg s (often more than one, leading to multiple birth s). Low sperm count may be overcome by limiting intercourse to the time of ovulation, the most fertile period. If these methods are unsuccessful, couples may try artificial insemination , in vitro fertilization , or surrogate motherhood , or they may choose adoption instead.