Final answer:
A diaphragm should be inserted before intercourse with spermicide and left in place for at least six hours post-intercourse. It has about a 12% failure rate and does not protect against STIs.
Step-by-step explanation:
A diaphragm should be inserted vaginally before sexual intercourse, and it must be placed over the cervix to effectively prevent pregnancy. It is recommended to cover the diaphragm with spermicide before insertion for additional protection against pregnancy. The diaphragm should be left in place for at least six hours after intercourse to ensure its effectiveness. While the failure rate of diaphragms with typical use is approximately 12 percent, it is important to note that they do not offer protection against sexually transmitted infections (STIs) and could be associated with an increased risk of urinary tract infections.