Sterility is the inability to create offspring (children), possibly as a result of a procedure—such as tubal ligation, hysterectomy, or vasectomy. This is different from infertility, which is defined as the trying to conceive with appropriate, timed, and unprotected intercourse for twelve months without success. The duration of time is shortened to six months if the woman is 35 years or older. Other reasons the duration may be shortened are anovulation (when the female partner is not ovulating) or male factors (low sperm count or motility).