Final answer:
The diaphragm should remain in place for at least 6 hours after intercourse to be effective in preventing pregnancy, should be used with spermicide, and does not prevent STIs.
Step-by-step explanation:
After sexual intercourse, the diaphragm should remain in place for at least 6 hours to ensure effectiveness in preventing pregnancy. Diaphragms act as a barrier, preventing sperm from passing through the cervical canal into the uterus. For optimal use, it should be covered with spermicide before insertion. While diaphragms are effective in contraception with a failure rate of about 12 percent, they do not prevent the spread of sexually transmitted infections (STIs) and may increase the risk of urinary tract infections.