Barrier Methods of Contraception
Barrier methods of contraception act to physically prevent egg and sperm from coming into contact.
Basically, this is attempted by:
The human sperm cell is normally able to swim - propelled by a long tail called a flagellum. When sperm cannot move, they are much less likely to reach the egg. Further, when sperm are not normally motile, that is not swimming strongly, it is often a sign of being more generally impaired, and overall less likely to accomplish fertilization even if they did reach the egg.
Barrier methods include condoms for men, diaphragms, cervical caps, condoms for women, and spermicides.
Condoms for men
Condoms are a thin, strong, non-porous tube of material that fits over the glans and shaft of the erect penis. One name for them that was once popular is "sheaths", and - like that kind of dress, condoms are fairly form fitting and simple in design. Historically, condoms were made from natural materials, such as sheep intestines. However, synthetic materials, such as latex, are more effective for containing semen, and also offer some protection against infective agents that are much smaller than sperm cells, such as viruses.
Condoms have become increasingly available to the public in most parts of the world since the AIDS crisis, and are the only form of contraception that (when used correctly) can both reduce the risk of pregnancy and the transmission of sexually transmitted infections.
Even when condoms are high quality, contain spermicide, and are used appropriately, pregnancy (and venereal disease including AIDS) occur(s) in some women. Why is that? Leakage, breakage and inadvertant technical error are some of the reasons.
Effectiveness of male condoms
Failure rates vary according to relative risk of users. While condoms are said to be 98% effective in preventing both pregnancy and spread of venereal infections, these statistics consider all users, and not just highest risk users. If a woman is having vaginal sexual intercourse (coitus) with a fertile man while ovulating, this 98% statistic may not apply even if the condom is used perfectly; similarly, if over a year's course a hundred HIV-negative women had all intercourse with men who were not only HIV-positive, but had high titers of HIV and were actively shedding virus, it can not be concluded that only 2 of them would become HIV-positive. This 98% effectiveness rate involves the statistical realities that women sometimes have coitus when they are not fertile, and that people sometimes have sex with men who do not have any sexually transmittable diseases. For these reasons, most physicians advise discretion in choosing sexual partners for all men and women as part of the practice of 'safe sex', and awareness of the days of maximal fertility for women using barrier methods for contraception to increase chances of avoiding an unwanted pregnancy.
Protection varies according to compliance: "typical use" is less effective than "perfect use". All that is known about the effectiveness of male condoms has been estimated from retrospective studies in which particpants were asked about their birth control methods. Although condoms do have effectiveness as contraception, and the rates quoted here have been derived from this evidence, the actual rate of effectivenesss among groups of users is not precisely known.
Male condoms, like some other barrier methods, require an act of volition on the part of those who use them in each instance of sexual intercourse. Further, if pregnancy and sexually transmitted disease are to be prevented, the penis cannot touch a womans genital area unless properly covered by a condom. Using a condom - but only after such touching, or allowing such touching after the removal of the condom - when semen is still on the skin of the penis, markedly reduces protection. For these reasons, experts caution that effectiveness is greatest when male condoms are used by a motivated couple. In other circumstances, the failure rate of condoms is certainly not 2%. In one study in the USA, the first-year failure rates for male condom use was between 3% and 6% when the woman was over age 30 but between 8% and 10% when the woman was under age 25.[3] According to a current obstetrics textbook, "Pregnancy rates for the condom are reported to be from 1.6 to 21 per 100 woman-years, depending on the age and motivation of the population studied." [4]
Latex Allergy
Latex allergy causes symptoms which may be very severe for allergic individuals who have skin contact with latex materials. If a man is allergic to latex, he cannot safely use a latex condom without a threat to his health. If his female mate is allergic to latex, and he is not, he cannot use a latex condom without a threat to her health. In either case, latex condoms are ruled out as a method of contraception.
Since the 1990's, an alternative to latex condoms has been marketed. Polyurethane condoms and synthetic elastomer condoms are not allergenic to individuals with sensitivities to latex, and, because they resist oxidation, have a long shelf-life and are compatible with oil-based lubricants. However, the non-latex condoms break more easily than latex condoms and there are no good data, presently, to show whether or not they are as effective for contraception. Some non-latex condoms are not form-fitting, and have been shown to be ineffective contraceptives. [5].
The word 'spermicide' is usually used to refer to a product that is applied specifically for its spermicidal qualities. Spermicides are often used with, or incorporated into, other medical means of contraception. Technically, a spermicide is any material that is toxic to sperm, and, despite the "-cide" suffix, may not kill sperm so much as disable them sufficiently to halt their mobility. Some chemical spermicides are applied to condoms, or locally applied inside the vagina. However, the action of some medical contraceptives that are not ordinarily considered to be spermicides is, in fact, spermicidal. For example, the copper-containing IUDs primarily prevent fertilization by their toxic actions on sperm. Spermicides change the cell membrane of sperm and therefore make sperm inactive. Nonoxynol-9, a widely used spermicide, can cause epithelial damage to the lining of the vagina and rectum, and this damage can increase the risk of transmission of HIV. Nonoxynol-9 is the only spermicide approved for use in the USA. "In general, when used alone, spermicides have a failure rate of approximately 15% per year with perfect use but double that rate with typical use." [6]
Since the increased risk of HIV transmission was reported by the World Health Organization in 2001, spermicides have been considered potentially problematic as contraceptives for monogomous women whose mates may be bisexual or using intravenous drugs, and for women who have many sexual partners, especially if not used in conjunction with male condoms, which offer some protection from the virus.
Female Barriers: Diaphragm, Others
Some of the female barrier methods have been in use for decades, and rates of effectiveness are fairly well known. Others, such as the female condom, are much newer and there is relatively little clinical evidence for how effective these methods are in actual use.
Condoms for women
The female condom has theoretical advanatges. However, the device has not been used widely enough or long enough to have its clinical efficacy tested. It may or may not offer as much protection as the male condom.
The female condom is a loose tube of thin material (polyethelene) that extends between two rings, one which fits in the vagina and the other which fits over the external genitalia. It is not made out of latex, and therefore is not a problem for those with latex allergy. Since it completely covers the genital contact area between men and women during coitus, it should help reduce the transmission of some STIs, particularly genital herpes as well as the rate of pregnancy, and -unlike the male condom, which is worn over the penis- is more completely controlled by the woman who uses it. However, the female condom is not nearly as well studied as the male condom, and the actual failure rates and effectiveness in preventing disease transmission are not known at this time.
There are other differences which may be helpful in some circumstances, the female condom is inserted before beginning sexual activity and can be left in place for a longer time after ejaculation.
The cervical cap requires skill for proper use. Even in skilled hands, and with good compliance reported, it is at best only 95% effective as a contraceptive.
The cervical cap is a flexible rubber (or plastic) cup-like dome placed over the cervix, that has been in use for several decades — mostly in Europe. A spermicide is placed in the cap before use and is an important component for effectiveness. The flexible cap is depressed while being positioned over the cervix by the user and is then held in place by suction, once released.
Cervical caps are not sold over the counter but must be carefully sized by health care providers. Caps require office or clinic visits for fitting, and personal instruction for use. Proper technique involves considerable skill on the part of the user. Even with consistent use, technical errors lead to pregnancy in 5% or more of women using this method.
Failure rates with the cervical cap are similar to those with the diaphragm. In one large, randomized clinical trial, 1-year pregnancy rates were 17.4% for the cap and 16.7% for the diaphragm.[3]
There has been speculation that the cap may help reduce sexually transmitted infections, but this device still allows the kind of genital contact that ordinarily transmits herpes simplex and genital warts, and there have been no studies that prove any reduction in sexually transmitted infections.
Diaphragms are circles of synthetic material held by a flexible ring. These are folded and placed in the vagina by the user. When inserted properly, the device unfolds when released, covering the cervix. Diaphrams must be carefully fitted by a health care provider in the office or clinic in order for a woman to receive the correct size. The proper size is the largest size that fits without putting pressure on the surrounding vaginal mucosa. Devices that are too large or left in place for too long can ulcerate the vaginal mucosa (the lining of the vagina). Women whose uterus makes a sharp angle with the vagina, or who have short vaginas, cannot ordinarily use diaphragms effectively.
Spermicides are recommended for use with the diaphragm. Jellies or creams of spermicides are placed on the device before it is inserted, on the side that will be facing the cervix. The diaphragm should be left in place for at least 8 hours after the last episode of sexual intercourse. If there is more than one episode, then additional spermicide is to be placed in the vagina before each, leaving the diaphragm in place. There are some variations in the details of recommended use depending on individual experts.
Diaphragms have been in use for decades, predating the AIDS era. There is no good evidence that diaphragms prevent sexually transmitted disease. Although in some cases the diaphragm may act as a barrier that reduces infection, the use of spermicides and the possibility of ulceration with poorly fitting devices make the overall benefit doubtful. As with the genital cap, use of this device allows (essentially) full contact between the penis and vaginal mucosa, and offers no protection of surrounding areas, so that there is no reason to expect protection from transmission of venereal warts or herpes. Failure rates with the diaphragm (as a contraceptive) range from about 5%, for experienced long-time users who are part of a motivated couple, to 20%, for general use. [3]
Diaphragm use is associated with an increased number of urinary tract infections in the women who use them.