How does a diaphragm work in the body?

As a barrier: The diaphragm acts as a barrier to prevent sperm from getting into the uterus and joining with eggs to prevent pregnancy. Diaphragms should be used with a spermacide gel or cream to make them more effective.

Barrier method: A diaphragm is a physical barrier to the passage of sperm from the vagina to the cervix. If, as recommended, a spermicide is added to the inside cup of the diaphragm, it is also chemical barrier as well with a combined efficacy of the 90th percentile.