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Cervical cap

The cervical cap is form of barrier contraception. A cervical cap fits over the cervix and blocks sperm from entering the uterus through the external orifice of the uterus, called the os. This article includes the Lea's Shield device, which is considered by some sources to be a different type of cervical barrier.

Terminology

The term cervical cap has been used to refer to a number of barrier contraceptives, including in modern times the Prentif, Dumas, Vimule, and Oves devices. In the United States, Prentif was the only brand available for several decades (Prentif was withdrawn from the U.S. market in 2005). During this time, it was common to use the term cervical cap to refer exclusively to the Prentif brand. Currently, some sources use cervical cap to refer to the recently introduced devices FemCap and Lea's Shield. Other sources include FemCap in the term cervical cap, but classify the Lea's Shield as a distinct device.

History

Ancient

The idea of blocking the cervix to prevent pregnancy is thousands of years old. Various cultures have used cervix-shaped devices such as oiled paper cones or lemon halves. Others made sticky mixtures that included honey or cedar rosin, to be applied to the os. The modern idea of a cervical cap as a fitted device that seals itself against the vaginal walls is of more recent origin; it emerged within the past century.

1800s

In 1838, German gynecologist Friedrich Wilde created the first modern cervical cap by making custom-made rubber molds of the cervix for some of his patients. These caps were probably short-lived, as uncured rubber degrades fairly quickly. An important precursor to the invention of more lasting caps was the rubber vulcanization process, patented by Charles Goodyear in 1844.

Over the next several decades, the cervical cap became the most widely used barrier contraceptive method in Western Europe and England. Although the diaphragm was always more popular in the United States than the cervical cap, the cap was also common.

1900s

Many designs were developed in the later nineteenth and early twentieth century. The Vimule cap became available as early as 1927. The Prentif brand cap was introduced in the early 1930s. The Dumas cap was initially made of plastic, and was available by the 1940s. Lamberts (Dalston) Ltd. of the UK manufactured these three cap types. Other types of caps had stems to hold them in place in the cervix; some of the stems actually extended into the uterus. These stem pessaries became precursors to the modern intrauterine device.

Use of all barrier methods, but especially cervical barriers, dropped dramatically after the 1960s introduction of the combined oral contraceptive pill and the intrauterine device. In 1976, the U.S. government enacted the Medical Device Amendment. This law required all manufacturers of medical devices to provide the FDA with data on the safety and efficacy of those devices. Lamberts (Dalston) Ltd., the only manufacturer at that time, failed to provide this information, and the FDA banned the use of cervical caps in the United States.

In the late 1970s, the FDA reclassified the cervical cap as an investigational device, and it regained limited availability. Within a few years, the FDA withdrew investigational status from the Vimule cap, following a study that associated its use with vaginal lacerations. In 1988, the Prentif cap gained FDA approval. The feminist movement played a large role in re-introducing the cervical cap to the United States. One paper called its involvement at all steps of the FDA approval process "unprecedented.

Types

Several brands of caps have been manufactured during the late 1900s and early 2000s. They can be divided into two types: cavity rim caps, and other caps. Cavity rim caps adhere to the cervix, while other caps adhere to the vaginal walls around the cervix.

The cavity rim caps are Prentif, made of latex, and the disposable cap Oves, made of silicone. There are three sizes of Prentif: 22, 25, 28, and 31 mm. There are three sizes of Oves: 26, 28, and 30 mm. Unique among cervical caps, it adheres to the cervix by surface tension, rather than by suction.

The other devices are the latex Dumas and Vimule, and the silicone FemCap and Lea's Shield. There are five sizes of Dumas: 50, 55, 60, 65, and 75 mm. There are three sizes of Vimule: 42, 48, and 52 mm. There are three sizes of FemCap: 22, 26, and 30 mm. Lea's Shield is manufactured in a single size. Unlike the other caps, Lea's Shield has a one-way air valve that helps it seal to the vaginal walls. The valve also allows the passage of cervical mucus. Both Lea's Shield and FemCap have loops to assist in removal.

As of 2008, many of these devices are no longer being manufactured: Lea's Shield, Oves, Prentif, Vimule, and Dumas have been discontinued.

Fitting

Individuals who wish to use a cervical cap are screened by a health care provider to determine if a cervical cap, or one brand of cap, is appropriate for them. If a cap is determined to be appropriate, the provider will determine the proper size. The user must be refitted after any duration of pregnancy, whether the pregnancy is aborted, miscarried, or carried to term through vaginal childbirth or caesarean section.

Several factors may make a cap inappropriate for a particular woman. Women who have given birth may have scar tissue or irregularly shaped cervixes that interfere with the cap forming a good seal. For some women, available sizes of cervical caps do not provide a correct fit. Also, cavity rim caps are not recommended for women with an anteflexed uterus.

Obtaining a fitting appointment may be difficult for some women. A 1997 survey in the United States found that most family medicine residents had no experience with prescription methods of birth control other than oral contraceptives. In some countries, some devices (such as the Lea's Shield) are available without a prescription.

Use

The first step in inserting or removing a cervical cap is handwashing, to avoid introducing harmful bacteria into the vaginal canal. The cap is inserted prior to sexual intercourse; some sources state that insertion prior to sexual arousal decreases the risk of incorrect placement. Most sources recommend the use of spermicide with the cap, but some sources say spermicide use is optional.

The cap remains in the vagina for a minimum of 6 or 8 hours after the last intravaginal ejaculation. It is recommended the cap be removed within 72 hours (within 48 hours recommended in the U.S.) Other than the disposable Oves cap, after use cervical caps are washed and stored for reuse. Silicone devices may be boiled to sterilize them. Reusable caps may last for one or two years.

Effectiveness

The effectiveness of cervical caps, as of most forms of contraception, can be assessed two ways: method effectiveness and actual effectiveness. The method effectiveness is the proportion of couples correctly and consistently using the method who do not become pregnant. Actual effectiveness is the proportion of couples who intended that method as their sole form of birth control and do not become pregnant; it includes couples who sometimes use the method incorrectly, or sometimes not at all. Rates are generally presented for the first year of use. Most commonly the Pearl Index is used to calculate effectiveness rates, but some studies use decrement tables.

Contraceptive Technology reports that the method failure rate of the Prentif cervical cap with spermicide is 9% per year for nulliparous women (women who have never given birth), and 26% per year for parous women. The actual pregnancy rates among Prentif users vary depending on the population being studied, with yearly rates of 11% to 32% being reported.

Little data is available on the effectiveness of the Oves cap and Femcap. The Oves manufacturer cites one small study of 17 users. The Femcap website does not cite any data on the current version of the Femcap; but lists data for an older version which is no longer approved by the FDA.

The only effectiveness trial of Lea's Shield was too small to determine method effectiveness. The actual pregnancy rate was 15% per year. Of the women in the trial, 85% were parous (had given birth). The study authors estimate that for nulliparous women (those who have never given birth) the pregnancy rate in typical use may be lower, around 5% per year.

Acceptability

The Oves cap and the new version of the Femcap performed poorly in user acceptability studies. The study on the Femcap concluded that the modifications to the FemCap significantly increased pain and discomfort among female users and their male sex partners, and that the modifications decreased acceptability of the device compared with the earlier version. The study of the Oves cap reported that few women indicated that they would use the cap in the future.

A pilot study conducted in Britain prior to the Lea's Shield's approval concluded that the Lea's Shield "may be acceptable to a highly select minority of women".

As of 2002, the cervical cap was one of the least common methods of contraception in the United States. A 2002 study indicated that of sexually active American women, 0.6% are currently using either the cervical cap, contraceptive sponge, or female condom as their primary method of contraception, and fewer than 1% have ever used a cervical cap.