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15.7.3: Birth Control

Mechanical and/or Chemical Barriers

Male Condom

  • a sheath of thin, flexible material (e.g., latex) worn over the penis
  • effective if used carefully
  • also protects against sexually-transmitted disease (STD) agents such as
    • HIV, the cause of AIDs
    • herpes virus
    • human papilloma virus (HPV)
    • chlamydiae
    • Neisseria gonorrhoeae, the cause of gonorrhea

Female Condom

  • a thin-walled pouch inserted into the vagina
  • protects against sexually-transmitted diseases (STDs)
  • less effective than the male condom

Diaphragm

  • rubber dome placed at the upper end of the vagina
  • may be used along with spermicides

Cervical Cap

  • impermeable cap fitted over the cervix
  • best used with spermicides

Spermicides

  • chemicals, such as nonoxynol 9, that inactivate sperm. Inserted into the vagina — often incorporated in a sponge — prior to intercourse.
  • not very effective if used alone

Hormonal Contraception

Oral Contraceptives - the "Pill"

  • Many formulations combining varying amounts of a synthetic estrogen and a synthetic progestin (progesterone-like steroid)
  • taken for 3 weeks, then stopped to allow menstruation
  • most widely-used reversible method

Skin ("Transdermal") Patch

  • The Ortho Evra® patch releases an estrogen and a progestin through the skin.
  • A fresh patch is applied each week for 3 weeks, and then a week without allows menstruation.
  • The failure rate is about 9%.

Vaginal Ring

  • a small plastic ring inserted into the vagina
  • NuvaRing® releases both an estrogen and a progestin.
  • It is left in place for 3 weeks and then removed for a week to allow menstruation.
  • The failure rate is about 9%.

Injectable Contraceptive

  • An injection containing a synthetic progestin (depot medroxyprogesterone acetate or "DMPA")(Depo-Provera®)
  • One injection given every three months inhibits the release of GnRH, thus inhibiting the synthesis of FSH and LH and blocking ovulation.
  • One of the most reliable methods of birth control.

Contraceptive Implant

  • Implanon® and Nexplanon®, each a tiny (40 x 2 mm) flexible plastic rod that releases a synthetic progestin is inserted under the skin (requiring a local anesthetic).
  • Prevents pregnancy for up to 3 years.
  • If pregnancy is desired sooner, is easily removed (again requiring a small incision and a local anesthetic) and normal fertility quickly returns.
  • Although used by only ~1% of U.S. women, implants are among the most effective of the birth control methods.

"Morning After" Pill

The most popular formulation in the U.S., called Plan B One-Step®, contains a high dose of a progestin. If taken within 72 hours after unprotected intercourse, the drug interferes with ovulation and, if ovulation has occurred, with fertilization.

If so many days have elapsed that implantation has occurred, RU-486 may be used. RU-486 is a synthetic steroid related to progesterone. Unlike the progestins discussed above, that mimic the action of progesterone, RU-486 blocks the action of progesterone. (Synthetic molecules that mimic the action of a natural molecule are called agonists; those that oppose it are antagonists.) RU-486 (also known as mifepristone) is a progesterone antagonist. It binds to the progesterone receptor, and in so doing prevents progesterone itself from occupying its receptor. Thus the gene transcription normally turned on by progesterone is blocked, and the proteins necessary to begin and maintain pregnancy are not synthesized. Because RU-486 is used after implantation, it is causing an early abortion and thus has been subjected to controversy.

Intrauterine Devices (IUD)

  • The intrauterine device (IUD) is a device, usually T-shaped, inserted into the uterus by a physician.
  • Two types available in the U.S.:
    • ParaGard®, which is coated with copper wire and can be left in place for 10 years;
    • Mirena®, which releases a progestin and can be left in place for up to 5 years.
  • Although used by only 8.5% of U.S. women, IUDs are among the most effective of the birth control methods. Only about 1 woman in a thousand becomes pregnant during her first year of using Mirena®.

Natural Family Planning - Rhythm Methods

  • An egg must be fertilized on the day of ovulation.
  • Sperm can live in the female reproductive tract for up to 6 days.
  • So copulation that takes place more than 5 days before or a day after ovulation is unlikely to lead to pregnancy.
  • Abstinence during this period is called natural family planning or the rhythm method.
  • Its success (which is low) depends upon being able to determine accurately just when ovulation occurs.
  • Highly-motivated women can do this by
    • monitoring their body temperature (which rises slightly at ovulation)
    • the amount and consistency of the mucus secreted by their uterus, and more recently
    • measuring the concentration of estrogen and/or progesterone in the urine (which mirrors the level in the blood).
  • It is favored by those who do not currently want a baby, but do not wish to use contraceptive devices (about 1% of U.S. couples).

Abortion

  • the deliberate removal of the embryo or fetus before it is ready for birth
  • Done
    • mechanically
      • using a suction device (during the first 3 months of pregnancy)
      • using surgery (later in pregnancy)
      or
    • chemically (using RU-486 and prostaglandins) during the first 7 weeks of pregnancy

All methods of birth control have been the subject of controversy (except for natural family planning).

  • In general, the controversy over a given method is proportional to the lateness of the stage of the reproductive process.
  • So not surprisingly abortion is a particularly controversial procedure especially when it is induced in the later stages of pregnancy.
  • Nevertheless, worldwide some 46 million pregnancies are terminated each year by induced abortion.

Sterilization

Roughly one-third of U.S. couples still in their reproductive years have chosen for one or the other to be sterilized.

Tubal Ligation

Fig. 15.7.3.1 Tubal ligation

  • Both fallopian tubes (oviducts) are cut and tied so that no egg can be fertilized.
  • Requires incision(s) and so must be done under anesthesia.

Vasectomy

  • Each vas deferens is cut near the top of the scrotum.
  • Can be done in the doctor's office, with a local anesthetic, in 30-40 minutes.
  • Testosterone secretion by the testes is not inhibited.
  • Does not stop the production of the various glandular secretions that make up the bulk of the semen.
  • Copulation and ejaculation proceed normally.
  • Sometimes the operation can be reversed, but don't count on it.

Quinacrine Sterilization (QS)

  • Pellets of the antimalarial drug quinicrine are placed (by a physician) in the uterus
  • Done twice, a month apart.
  • Causes scarring of the fallopian tubes
  • Clinical trials are in progress in the U.S.

Summary

Popularity (% using the method) and relative effectiveness of several methods of birth control among U. S. women using contraceptives. The pregnancy rate is the number of pregnancies per 100 women in the first year of using the method.
Method Popularity Pregnancy Rate
Natural family planning (rhythm) 1% 25
Male condom 16% 17
Oral contraceptives ("the pill") 28% 0.3–8.7*
Intrauterine devices (IUD) 8.5% 0.1–1.0*
Implants, e.g., Implanon® ~1% 0.05–1.0*
DMPA injections ~3.5% 6.7
Male + Female Sterilization 37% <<1%
None   85
* The lower value is found under ideal conditions; i.e., among highly-motivated women receiving good medical care.

The bottom line: The failure rate of the pill, patch, and vaginal ring, as they are commonly used, is 20 times that in women using an IUD, or implant.

Future Prospects

  • Not too bright because pharmaceutical houses are reluctant to invest the huge amounts of money and time needed to develop products that expose them to controversy, put them at risk of lawsuits and whose largest market is in countries too poor to afford them.
  • Research on possible male birth control pills is going on. However, it is not yet easy to see how spermatogenesis can be blocked without causing undesirable side-effects.
  • Some research is proceeding on contraceptive vaccines; that is, using the immune system to block one or another step in the process (e.g. fertilization). Examples: vaccines to raise antibodies
    • against gonadotropin-releasing hormone, GnRH (for males)
    • against human chorionic gonadotropin, HCG (for females)
    • to immobilize sperm (also for females)
    But, what risks such antibodies might present is not at all clear.

Contributors