Birth control methods may be categorized into several groups based on their mode of action: hormonal, chemical and behavioral contraceptive methods, anti-implantation devices, sterilization, and induced abortion.

Contraception

Contraception is the prevention of conception, which is the union of sperm nucleus and ovum nucleus. Contraceptive methods are designed to prevent sperm from reaching and penetrating a secondary oocyte, which leads to the formation of an ovum. There are several types of contraceptives,

including the use of hormones, barriers to sperm, spermicides (chemicals that kill sperm), and behavioral methods.

Hormonal Methods

Hormonal birth control methods use a higher concentration of synthetic progesterone and a lower concentration of synthetic estrogens to prevent ovulation. These hormones provide a negative-feedback control that inhibits the secretion of GnRH by the hypothalamus, which reduces the secretion of FSH and LH by the anterior lobe of the pituitary. This prevents maturation of ovarian follicles so ovulation does not occur. Use of hormonal birth control methods is timed to a woman’s menstrual cycle.

Hormonal birth control methods are very effective, but some women may experience unpleasant side effects, such as headache, irregular menstruation, nausea, and bloating. Women who smoke or have a history of blood clots, stroke, heart disease, liver disease, or uncontrolled diabetes have an elevated health risk when using hormonal birth control methods.

There are several ways to use hormonal birth control. The oral contraceptive, “the pill,” was the first available method of delivery, and it is still widely used. Several types are available, but the combination pill, which contains both synthetic progesterone and estrogens, is most commonly used. One pill is taken each day for three weeks of the menstrual cycle.

Some combination birth control pills may be used in higher dosages as morning after pills (MAPs), for postcoital emergency contraception. When used within 72 hours of unprotected intercourse, the hormone combination disrupts normal hormonal controls and tends to prevent either fertilization or implantation.

A birth control patch is a small adhesive skin patch containing the synthetic hormones. It is applied to the skin, and the hormones are absorbed through the skin. A new patch is used each week for three weeks.

A vaginal ring is a soft plastic ring that is wedged into the superior part of the vagina, where it remains and releases synthetic hormones over a three-week period. It is removed at the start of the fourth week.

Norplant is a set of tiny silicone rods containing synthetic progesterone that are surgically implanted deep to the skin of the arm or over the scapula. The released progesterone acts similarly to an oral contraceptive by inhibiting ovulation, and the implant is effective for up to five years. The implant may be removed to terminate contraception.

Depo-Provera is a synthetic progesterone that is administered by muscular injection at three-month intervals. It protects against pregnancy by preventing ovulation and altering the endometrium to inhibit implantation of a preembryo. Its use often causes weight gain as a side effect, and it can be a considerable health risk, so it must be used under a physician’s care. Women with a personal or strong family history of high blood pressure, asthma, kidney disease, migraine headaches, or breast cancer are at increased risk if using Depo-Provera.

Barriers

There are three types of barriers that are designed to prevent sperm from entering the uterus: condom, diaphragm, and cervical cap.

Condoms act by preventing sperm from being deposited in the vagina. A male condom is a thin sheath of latex rubber that is slipped over the penis prior to sexual intercourse. A female condom is a thin polyurethane bag with a flexible ring at each end. The woman inserts the bag into the vagina prior to sexual intercourse. Condoms reduce but do not eliminate the chance of infection by sexually transmitted diseases (STDs).

A diaphragm is a dome-shaped sheet of rubber supported by a firm but somewhat flexible ring. It is placed in the superior vagina over the cervix prior to intercourse. It prevents sperm from entering the uterus. Spermicidal substances are used along with a diaphragm.

A cervical cap is a thimble-shaped piece of latex rubber that fits snugly over the cervix. Spermicidal substances are used with a cervical cap. Females with abnormal Pap smears or cervical infections should not use a cervical cap.

Spermicides

A variety of spermicides are available, including creams, jellies, and suppositories. These chemicals kill sperm by destroying their plasma membranes.

Behavioral Methods

The rhythm method requires abstinence from sexual intercourse from three days before the day of ovulation to three days after ovulation, for a total of seven days. It is based on the fact that the secondary oocyte may be penetrated by a sperm for only about 24 hours after ovulation. One difficulty with this method is determining the time of ovulation, because few women have perfectly regular cycles. The failure rate is higher in women who have irregular cycles.

Withdrawal, or coitus interruptus, is the removal of the penis from the vagina just prior to ejaculation. Failures of this method result from preejaculatory emission of semen or failure to withdraw before ejaculation.

Anti-Implantation Devices

An intrauterine device (IUD) is a small plastic and copper object that is inserted into the uterus by a physician. The IUD causes inflammation of the endometrium, preventing implantation of a preembryo. An IUD may remain in place for long periods of time, but it should be checked at regular intervals by a physician because an IUD may be spontaneously expelled from the uterus. Undesirable side effects include excessive menstrual bleeding, painful cramps, and an increased risk of pelvic inflammatory disease and infertility.

Sterilization

Sterilization surgeries may be performed on both males and females. In males, a vasectomy is performed by cutting and blocking the vasa deferentia within the scrotum so that sperm do not form part of the semen. The sperm disintegrate and are reabsorbed. In females, a tubal ligation is performed through a small abdominal incision. The uterine tubes are cut and blocked to prevent the transport of a secondary oocyte toward the uterus. The ovulated secondary oocytes disintegrate and are reabsorbed. Vasectomies and tubal ligations do not affect the production of sex hormones or the sexual response.

Induced Abortion

An abortion is the premature expulsion of an embryo or fetus from the uterus. Spontaneous abortions are called miscarriages. They usually result from hormonal disorders or serious abnormalities of the developing embryo. An induced abortion may be used to terminate an unwanted pregnancy. Induced abortion involves dilation of the cervix and removal of the embryo or fetus by suction or surgical means. Possible side effects of induced abortions include prolonged bleeding, perforation of the uterus, and emotional trauma.

The so-called abortion pill, mifepristone (RU 486), is a progesterone antagonist. It causes the endometrium to break down, thereby detaching the embryo or fetus, which is passed from the uterus after administration of prostaglandins to promote uterine contractions. Its use is limited to the first five weeks of pregnancy and requires the supervision and care of a physician.

Effectiveness of Birth Control Methods

Effectiveness values are approximate because they vary with how the birth control methods are used.

Effectiveness is the percentage of women who do not become pregnant in one year while using this method of birth control.

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