The diaphragm and the cap
These are flexible silicone domes placed high in the vagina to cover the cervix. They form a mechanical barrier, but not a watertight one: they are always used with a spermicide. It is the pairing that gives the effectiveness, not the device alone.
- Insertion: before intercourse, up to two hours ahead. A dose of spermicide goes into the dome.
- Left in place: at least six hours after the last act, and no more than 24 hours in total.
- A further act in that time: add spermicide without removing the device.
- Size: some models are fitted after an examination, others come in one size. Significant weight change, childbirth or pelvic surgery are reasons to recheck the fit.
- Reusable for one to two years, washed with water and mild soap.
The cervical cap follows the same logic, smaller. It is clearly less effective in women who have given birth, the cervix having changed shape.
Spermicides
Creams, pessaries, gels or sponges containing a substance that immobilises and destroys sperm, most often nonoxynol-9. Used alone they are among the least reliable methods. Their place is as a supplement.
Another product, recent and available in only a few countries, works differently: it keeps the vaginal pH acidic during intercourse, which immobilises sperm rather than destroying them. It is applied just before each act and its effectiveness remains that of a local method.
Effectiveness
| Perfect use | Typical use | |
|---|---|---|
| Diaphragm with spermicide | around 16 | around 17 |
| Spermicides alone | around 16 | around 21 |
| Sponge, never given birth | around 9 | around 14 |
| Sponge, has given birth | around 20 | around 27 |
Pregnancies per 100 women per year.
These figures are unambiguous: roughly one woman in five is pregnant within the year on spermicide alone. These methods are chosen with eyes open, usually because no hormonal method is wanted or possible.
Nonoxynol-9: a warning worth knowing
Repeated, frequent use of nonoxynol-9 irritates the vaginal lining and can therefore increase the risk of HIV transmission rather than reduce it. It is not advised for people at high infection risk or having very frequent intercourse. Spermicides protect against no sexually transmitted infection — that belief is old and wrong.
Who they can suit
Someone who refuses or cannot tolerate hormones, wants a method used only when needed and controlled by herself, and accepts the corresponding level of effectiveness. Always adding a condom improves protection substantially, against pregnancy and infection alike.