Many methods are used to prevent or terminate pregnancy, including methods that prevent fertilization (contraception), prevent implantation of the developing embryo (IUDs), or remove the implanted embryo or fetus (abortion). Many of these techniques are quite effective when done properly and used consistently.

Behavioral Methods

Abstinence, or refraining from sexual intercourse, is a sure way to prevent pregnancy when practiced consistently. It is not an effective method when used only occasionally.

Coitus interruptus is removal of the penis from the vagina just before ejaculation. This is a very unreliable method of preventing pregnancy, since it requires perfect awareness, and willingness to withdraw the penis at the correct time. It also ignores the fact that some sperm cells are found in pre-ejaculatory emissions.

The rhythm method requires abstaining from sexual intercourse near the time of ovulation. A major factor in the success of this method is the ability to predict accurately the time of ovulation. Although the rhythm method provides some protection against becoming pregnant, it has a relatively high rate of failure, resulting from both the inability to produce the time of ovulation and the failure to abstain around the time of ovulation.

Barrier Methods

A condom is a sheath of animal membrane, rubber, or latex. Placed over the erect penis, the condom is a barrier device, because the semen is collected within the condom instead of within the vagina. Condoms also provide protection against sexually transmitted diseases.

A vaginal condom also acts as a barrier device. The vaginal condom can be placed into the vagina by the woman before sexual intercourse.

Methods to prevent sperm cells from reaching the oocyte once they are in the vagina include use of a diaphragm, spermicidal agents, and a vaginal sponge. A diaphragm is a flexible plastic or rubber dome that is placed over the cervix within the vagina, where it prevents passage of sperm cells from the vagina through the cervical canal of the uterus. The most commonly used spermicidal agents are foams or creams that kill the sperm cells. They are inserted into the vagina before sexual intercourse. A sponge, either natural or synthetic, is permeated with spermicidal agents and placed over the cervix, where it acts as a barrier and kills the sperm cells. When used in combination, condoms, foams, creams, and sponges are much more effective than when they are used alone. Spermicidal douches, which consists of injecting stream of fluid, containing a chemical toxic to sperm cells, into the vagina. The stream of fluid removes and kills sperm cells. Spermicidal douches used alone are not very effective.

Lactation

Lactation prevents the menstrual cycle for a few months after childbirth. Action potentials sent to the hypothalamus in response to suckling that cause the release of oxytocin and prolactin also inhibit FSH and LH release from the anterior pituitary. Therefore lactation prevents the development of ovarian follicles and ovulation. Despite continual lactation, the ovarian and uterine cycles eventually resume. Because ovulation occurs before menstruation, relying on lactation to prevent pregnancy is not consistently effective.

Chemical Methods

Synthetic estrogen and progesterone in oral contraceptives (birth control pills) effectively suppress fertility in females. These substances may have more than one action, but they reduce LH and FSH release from the anterior pituitary. Estrogen and progesterone are present in high enough concentrations to have a negative-feedback effect on the pituitary, which prevents the large increase in LH and FSH secretion that triggers ovulation. Over the years, the dose of estrogen and progesterone in birth control pills has been reduced. The current low-dose-birth control pills have fewer side effects than earlier dosages. There is an increased risk of heart attack or stroke in women using oral contraceptives who smoke or have a history of hypertension or coagulation disorders. For most women, the pill is effective and has a minimum frequency of complications, until at least age 35.

Progesterone-like chemicals, such as Depo-Provera, which are injected intramuscularly and slowly released into the circulatory system, can act as effective contraceptives. Injected progesterone-like chemicals can provide protection from pregnancy for approximately a month, depending on the amount injected. A thin silastic tube containing progesterone-like chemicals, such as the Norplant system, can be implanted beneath the skin, usually in the upper arm. The progesterone-like chemicals are slowly released into the circulatory system. The implants can be effective for periods of up to 5 years.

Advantages of the injected and implanted progesterone-like contraceptives over other chemical methods of birth control are that they do not require taking pills on a a daily basis. The long-term effect of the injected and implanted progesterone-like chemicals have not been as thoroughly studied as birth control pills, and they are still being evaluated.

A new drug, RU486, blocks the action of progresterone, causing the endometrium of the uterus to slough off as it does at the time of menstruation. Therefore it can be used to induce menstruation and reduce the possibility of implantation when sexual intercourse has occurred near the time of ovulation. It can also be used to terminate pregnancies.

Surgical Methods

Vasectomy is a common method used to render males permanently incapable of fertilization without affecting the performance of the sex act. Vasectomy is a surgical procedure used to cut and tie the ductus deferens from each testis within the scrotal sac. This procedure prevents sperm cells from passing through the ductus deferens and becoming part of the ejaculate. Because such a small volume of ejaculate comes from the testis and epididymis, vasectomy has little effect on the volume of the ejaculated semen. The sperm cells are reabsorbed in the epididymis.

A common method of permanent birth control in females is tubal ligation, a procedure in which the uterine tubes are tied and cut or clamped through an incision made through the wall of the abdomen. This procedure closes off the pathway between the sperm cells and the oocyte. Laparoscopy, in which a special instrument is inserted into the abdomen through a small incision, is commonly used so that only small openings are required to perform the operation. In some cases, pregnancies are terminated by surgical procedures called abortions. The most common method for performing abortions is the insertion of an instrument through the cervix into the uterus. The instrument scrapes the endometrial surface, and at the same time a strong suction is applied. The endometrium and the embedded embryo are disrupted and sucked out of the uterus. This technique is normally used only in pregnancies that have progressed less than 3 months.

Prevention of Implantation

Intrauterine devices (IUDs) are inserted into the uterus through the cervix, and they prevent normal implantation of the developing embryonic mass within the endometrium. Some early IUD designs produced serious side effects such as perforation of the uterus, and, as a result, many IUDs have been removed from the market. However, data indicate that IUDs are effective in preventing pregnancy.

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