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Biology LibreTexts

43.7C: Contraception and Birth Control

  • Page ID
    14137
  • Contraception, also known as birth control, is methods used to prevent pregnancy; some of these methods are more successful than others.

    LEARNING OBJECTIVES

    Describe the various methods of birth control and their associated failure rates

    KEY TAKEAWAYS

    Key Points

    • Barrier methods include those that prevent the sperm from reaching the egg ( condoms, diaphragms, cervical caps, sponges, and spermicides ); these methods have a failure rate of 15-24%.
    • Hormonal methods include those that prevent a woman from ovulating (oral birth control pills, hormone injections, and hormone implants); these have a failure rate of 8%.
    • Sterilization, such as a tubal ligation in a woman or a vasectomy in a man, is an extremely effective (although permanent) method of contraception, with a failure rate of 1%.
    • More “natural” methods of birth control include avoiding intercourse when a woman is ovulating, or withdrawing the penis from the vagina before ejaculation; these methods are much less successful, with a failure rate of around 25%.

    Key Terms

    • condom: a flexible sleeve made of latex or other impermeable material such as sheepskin, worn over an erect penis during intercourse as a contraceptive or as a way to prevent the spread of STDs
    • intrauterine device: a contraceptive device consisting of a spiral or similar shape of plastic or metal inserted through the vagina into the uterus in order to prevent the implantation of a fertilized egg
    • vasectomy: the surgical removal of all or part of the vas deferens, usually as a means of male sterilization
    • contraception: the use of a device or procedure to prevent conception as a result of sexual activity
    • spermicide: a substance used for killing sperm

    Contraception and Birth Control

    Contraception, also known as birth control, is methods or devices used to prevent pregnancy. Strictly speaking, contraception aims to prevent the sperm and egg from joining, while birth control can refer to methods used to prevent a fertilized egg from developing into a fetus. Both terms are, however, frequently used interchangeably.

    There are many methods of birth control, including barriers to sperm, hormones that prevent ovulation, sterilization procedures, and “natural” methods. Each method has an associated “failure rate”, which is the number of pregnancies resulting from the method’s use over a twelve-month period.

    Barrier methods include those that prevent the sperm from reaching the egg. These include condoms, diaphragms, cervical caps, sponges, and spermicides; they have a failure rate of 15-24%. Barrier methods such as condoms, cervical caps, and diaphragms serve to block sperm from entering the uterus, thereby preventing fertilization. Chemicals such as spermicides, which are designed to kill sperm, are often used in conjunction; sponges, for example, are saturated with spermicides and are placed in the vagina at the cervical opening. Combinations of spermicidal chemicals and barrier methods achieve lower failure rates than do the methods when used separately.

    Hormonal methods use synthetic progesterone (sometimes in combination with estrogen) to inhibit the hypothalamus from releasing FSH or LH, preventing an egg from being available for fertilization. The method of administering the hormone affects failure rate, although, in general, hormonal methods have a failure rate of 8%. The most reliable method, with a failure rate of less than 1 percent, is the implantation of the hormone under the skin. The same rate can be achieved through the sterilization procedures of vasectomy in the man or of tubal ligation in the woman, or by using an intrauterine device (IUD). IUDs are inserted into the uterus where they establish an inflammatory condition that prevents fertilized eggs from implanting into the uterine wall.

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    Intrauterine device: An intrauterine device, or IUD, is implanted inside a woman’s uterus, causing the uterus to respond with slight inflammation. This inflammation prevents a fertilized egg from implanting in the uterine wall.

    Sterilization is a one-time, permanent, surgical procedure. In a vasectomy, the vasa deferentia of a male are severed and then tied/sealed in a manner that prevents sperm from entering into the seminal stream (ejaculate). Tubal ligation or tubectomy is a surgical procedure for sterilization in which a woman’s fallopian tubes are clamped and blocked, or severed and sealed; either method prevents eggs from reaching the uterus for fertilization. Both of these procedures have a less than 1% failure rate.

    Natural methods include avoiding intercourse when ovulation is occurring (“natural family planning) or withdrawing the penis from the vagina before ejaculation. Nearly 25% of the couples using natural family planning or withdrawal can expect a failure of the method. Natural family planning is based on the monitoring of the menstrual cycle and having intercourse only during times when the egg is not available. A woman’s body temperature may rise a degree Celsius at ovulation and the cervical mucus may increase in volume, becoming more pliable. These changes give a general indication of when intercourse is more or less likely to result in fertilization. Withdrawal involves the removal of the penis from the vagina during intercourse, before ejaculation occurs; it has a failure rate of 27%. This is, therefore, a risky method. The high failure rate is due to the possible presence of sperm in the bulbourethral gland’s secretion, which may enter the vagina prior to removing the penis.

    Termination of an existing pregnancy can be spontaneous or voluntary. Spontaneous termination in the first trimester is referred to as spontaneous abortion, while in the second and third trimesters is referred to as a miscarriage. Spontaneous abortion usually occurs very early in the pregnancy (typically within the first few weeks). Pregnancy loss occurs when the embryo/fetus cannot develop properly so the gestation is naturally terminated. Voluntary termination of a pregnancy is called an elective abortion. Laws regulating elective abortion vary between states; the laws tend to view fetal viability as the criteria for allowing or preventing the procedure.