Each month as long as you have a menstrual cycle, female hormones act within an ovary to stimulate the growth of a Graafian follicle (a small sac that contains an egg). When the follicle is mature, it bursts, producing an egg. The egg is caught by one of the Fallopian tubes, which carries it toward the uterine cavity.

During the sex act, male ejaculation releases millions of sperm, but only one of them will reach the egg. Conception happens when a sperm enters the egg in the Fallopian tube, fertilizing it. The fertilized egg continues its journey into the uterine cavity, implanting itself in the wall of the uterus. This is the start of the embryo's development.

A birth-control method is any method that will impede conception.

In choosing a birth-control method, you should think how it will affect your life.

• Will it diminish the spontaneity of lovemaking?
• Are you comfortable enough to insert birth-control material before having sex?
• What about your partner?
• If the birth-control method must be used each time before intercourse, is it effective in preventing pregnancy?
• Does it also protect against sexually transmitted disease?

Every woman should keep this in mind: Except for abstinence, no birth-control method is 100% effective against pregnancy or against HIV (the AIDS virus) and other types of sexually transmitted disease (STDs).

Hormone-based birth-control methods -- the Pill, the skin implant Norplant and the injection Depo-Provera -- and the IUD (intrauterine device) are the most effective.

They're far more effective than the methods that must be used each time you have intercourse, which include the male condom and the female diaphragm, sponge, spermicides, cervical cap, condom, rhythm method, withdrawal and natural family planning.

The methods that include the use of spermicides, especially those containing Nonoxynol-9, have a better chance of protecting against some forms of STDs (sexually transmitted disease). When condoms are used along with another form of birth control, the chance of avoiding both pregnancy and STDs is higher.

Here are brief descriptions of the many types of birth control, how they work, the situations for which they are most appropriate, and how effective they are in preventing pregnancy.

The Pill
The Pill works by blocking the hormonal signal that causes the release and ripening of the follicle. It also alters mucous secretion from the cervix.

The Pill is designed to produce a natural monthly cycle -- only without the worry of becoming pregnant. Most birth-control pills contain two female hormones, estrogen and progesterone. A few have progesterone only, which makes them slightly less effective.

Once you decide to use the Pill, you should take one pill each day at the same time. If you miss taking your pill one or two days, you may experience irregular bleeding and may even become pregnant. When the Pill is used correctly, it is about 99% effective.

The Pill provides many benefits. You'll lose much less blood during your menstrual period and you're much less likely to have menstrual cramps. The Pill also protects against ovarian cancer, benign (non-cancerous) cystic diseases of the breast, and pelvic inflammatory disease.

The Pill DOES NOT protect against HIV and other STDs. Only "barrier" methods of contraception such as the condom or diaphragm, used in conjunction with s permicide (typically Nonoxynol-9) offer protection against STDs.

STDs are transmitted by penetration of viruses or bacteria through body membranes. A non-porous barrier between the membrane and the bacteria or virus helps prevent this penetration.

If you're still a cigarette smoker, you SHOULD NOT take the Pill. This is especially true if you're 35 or older. Preferably, smokers should quit completely before starting on the Pill.

After age 35, there is a high incidence of heart attacks and stroke in women who take the Pill and smoke. The risk is highest in women whose pills contain the largest amounts of hormones.

So far, however, there's no direct proof that using the Pill by women 35 and older increases their risk of heart attack and stroke.

When the Pill was introduced 40 years ago, the amount of estrogen was about three times higher than in today's Pill, and many women had problems with it.

At that time, women over the age of 35 were no longer able to use the Pill. Today's lower estrogen levels are safe for nonsmoking women over 35.

The birth-control pill is also useful for other medical conditions. Women age 40 or older have an increased risk of irregular bleeding. When tests prove that an irregularity is caused by a hormonal imbalance, a nonsmoking woman can be put on a low-dose pill and continue with it until she reaches 50, the average age of menopause. This procedure has saved many women from having hysterectomies.

The Pill can also help normalize the menstrual cycles of adolescents who have irregular bleeding and ovarian cysts.

Diaphragm
A diaphragm is a cup made of latex in which a spermicidal cream or jelly is placed and then inserted into the vagina, covering the cervix before intercourse. It acts as a barrier, keeping sperm from reaching the egg, and should any sperm get around the diaphragm, the jelly it contains is likely to kill them. If used correctly, a diaphragm can be 94% effective for birth control. It also may protect against STDs.

Diaphragm.

A diaphragm lets you plan ahead for sexual activity, since you can insert it up to six hours before intercourse. Be sure to remove it eight hours after the last act of intercourse. If you want to have intercourse more than once, simply leave the diaphragm in place and inject more jelly or cream into the vagina.

To work effectively, a diaphragm must be the correct size, and should be fitted by a health-care provider. If you've had a baby or if you've gained or lost more than 10 pounds, you should have your diaphragm refitted.

Using a diaphragm has some side effects, mostly because of the spermicide it is used with. Vaginal and penile irritation may occur, and some users have an increased risk of bladder infection.

Cervical Cap
Made of latex, a cervical cap is a smaller version of the diaphragm that is fitted directly to the cervix by the health-care practitioner. It can be placed any time before intercourse and left in place for over 48 hours. A cervical cap is used with spermicidal cream or jelly. It is approximately 94% effective and may protect against some STDs.

Cervical cap.

A user may have some difficulty removing the cervical cap. It may cause irritation of the penis and vagina, and in some cases may injure the cervix.

Spermicide
Spermicides -- chemicals or agents that kill sperm -- come in the form of cream, jelly, foam, film and suppositories. They may contain Nonoxynol-9. Spermicides are introduced in the vagina before sexual intercourse and work by killing sperm before they enter the cervix on their way to the egg.

If used properly on its own, a spermicide can be up to 93% effective. Using a spermicide with a condom is even more effective. Spermicides may also help to protect against HIV and some other STDs.

Spermicides.

Condom
Some condoms are made of latex, others from animal intestine. The animal-material condoms are porous and cannot stop the spreading of STDs. For this reason, only latex condoms should be used. Some come lubricated with spermicide, but others do not.

Condoms work by retaining semen, keeping the sperm from reaching the cervix. They also reduce the risk of transmitting or receiving HIV and other STDs. If correctly used alone, they can be 94% effective. They're even more effective when used with spermicide.

Condoms should be used only once and should always be stored in a cool place. Because latex deteriorates, they should NOT be carried in wallets and left in hot areas such as car glove compartments.

As petroleum-based lubricants such as Vaseline will harm the latex in condoms or diaphragms, use only K-Y Jelly or its pharmaceutical equivalent for lubrication during intercourse.

The effectiveness of condoms depends on their careful application, use and removal.

The man should place the rolled condom at the tip of the erect penis and unroll it toward the base of the penis, leaving the nipple-shaped tip empty. After ejaculation, while the penis is still erect, the penis should be removed from the vagina while holding the ring of the condom. This prevents the condom slipping off and sperm accidentally spilling into the vagina.

Here's an idea: Some couples make placing the condom part of their foreplay.

Condoms can cause vaginal and penile irritation. Unfortunately, many men refuse to use condoms because they alter sensation and satisfaction. Some women do not feel assertive enough to demand their use.

Male condom.

Female Condom
The new female condom may be the answer to women taking charge of their own safety.

The female condom is a polyurethane tube with a closed end and an open end. The closed end is supported by a ring that the user folds (much like a diaphragm) and inserts into the vagina, against the cervix. The open end, also supported by a ring, remains outside the vagina, protecting the surrounding tissues.

The female condom is used with its own lubricant and, like the male condom, is good for one use only. It can be inserted up to eight hours before intercourse, and must be removed immediately afterwards. It is new on the market, available over the counter, and its effectivity rate, when used correctly, is 97%.

A - female condom, B - female condom in place.

Rhythm Method
Women with regular menstrual cycles are the best candidates for this method. Ovulation occurs 14 days before the menstrual period, regardless of the length of the menstrual cycle. The egg is alive for about 24 hours after ovulation and live sperm remain in the woman's body for more than 48 hours after the last sex act. This method can be up to 93% effective if used properly.

To use the rhythm method, you need to check the time of ovulation by taking your temperature. About 24 to 36 hours before ovulation, you will note a drop in your temperature. Your temperature will climb again one to two days after ovulation, and will remain elevated thereafter.

To avoid pregnancy, you can abstain from intercourse for three days before the expected date of ovulation and three days afterward. ONLY USE THIS METHOD IF YOUR CYCLES ARE EXTREMELY REGULAR.

Douching
In some parts of the world, women have no access to birth control except douching after intercourse with a solution such as vinegar and water. Douching solutions, however, including those available commercially, DO NOT KILL SPERM. Moreover, immediately after ejaculation, sperm are sucked into the cervical canal, quickly traveling to the egg. For this reason, using douching as a method of birth control carries a high risk of pregnancy; nor does it protect against STDs.

A word of caution: "Douching is not that good for you". A study published in the Journal of Obstetrics and Gynecology supports the hypothesis that vaginal douching can predispose women to pelvic inflammatory disease (PID).

The study found that women who had douched during the previous 3 months had a PID risk 2.1 times greater than that of women who reported never having douched. Women who had douched once a week had a risk 3.9 times greater. Some possible reasons for a connection between douching and PID predisposition may be a more favorable environment for the growth of infectious agents and promotion of the upward spread of lower genital tract infection.

Coitus Interruptus or Withdrawal
Coitus interruptus, or withdrawal of the penis from the vagina before ejaculation, is a risky method of trying to avoid pregnancy. Its effectiveness is greatly reduced by the fact that the penile secretion that precedes ejaculation is highly saturated with sperm.

Prolonged Period of Breast Feeding
In Third World countries, many women use prolonged breast-feeding as a method of birth control because it delays the return of ovulation. During the time they breast feed, women don't menstruate.

But since ovulation occurs before menstruation, there's no way to predict when ovulation will resume, since it depends on the woman's size and state of nutrition. This means the woman may become pregnant before she even knows she can.

Five percent of breast-feeding women will ovulate within six weeks after childbirth, 25% will ovulate within three months, and 65% will ovulate after six months.

Natural Family Planning
This method teaches the physical signs that tell you when you can become pregnant, when you cannot become pregnant, and when not to have intercourse. To rely on this method for birth control, being very comfortable with your body and having a regular menstrual period are of the utmost importance.

Your sexual partner needs to learn this method as well, since its success requires real dedication by both of you. If practiced properly, it can be up to 95% effective against pregnancy. However, this method does not protect against STDs.

Norplant
Norplant consists of six soft, flexible, thin capsules implanted just under the skin of the arm in a fanlike patterns. The small capsules contain a type of progesterone that is released in a controlled manner for up to four years.

The capsules cannot be seen, though they can be felt through the skin. Norplant works by inhibiting ovulation and thickening the cervical mucus. The implants can be removed any time the woman wishes to become pregnant, and her fertility is immediately restored. However, removal may be more difficult than insertion.

Both insertion and removal must be done by a health-care provider.

Norplant is over 99% effective in women weighing under 150 pounds, but slightly less so if the woman weighs more. It does not protect against STDs.

Norplant.

Depo-Provera
This birth-control method is given by a health-care provider as an injection and is effective for three months. Depo-Provera works by preventing ovulation. It can even be given to a new mother right after childbirth, before she leaves the hospital. It is more than 99% effective against pregnancy, and does not offer protection against STDs.

Depo-Provera causes menstrual changes. When a woman first uses it, her menstrual cycles become irregular. After about a year, some women stop menstruating completely. After stopping the injections, there is a delay before fertility resumes.

Intrauterine Device (IUD)
An IUD is a piece of plastic partially covered with copper wires that is placed in the uterine cavity by a health-care provider. If you are fitted with an IUD, a string attached to it is left hanging from the cervix. This is meant to help you when you press on your cervix to make sure the IUD is in place.

The exact way an IUD prevents pregnancy is unknown. It could be by preventing implantation of the fertilized egg. The IUD is over 99% effective, and does not protect against STDs.

IUD in place.

An IUD can cause heavy menstrual flow and increases menstrual cramps in some women. Because of the risk of pelvic inflammatory disease, which in turn can cause sterility, the IUD is appropriate mainly for the woman who is in a monogamous relationship, has had at least two children, and has no history of pelvic inflammatory disease.

Some women's sexual partners have complained of discomfort caused by the IUD string.

Sterilization
Both men and women can be sterilized. In the man, a vasectomy is performed by localizing and cutting the vas deferens, the tubes that carry sperm from the testes. A vasectomy is a simple procedure performed by a physician under local anesthesia.

Vasectomy.

The procedure performed on women is a tubal sterilization, in which the Fallopian tubes are closed off by burning (cauterizing), cutting or clamping. This must be performed by a physician under general, epidural or spinal anesthesia.

Tubal ligation.

Tubal fulguration.

Sterilization is more than 99% effective in women. Sometimes, although rarely, a fistula or tiny hole develops in the severed tube and sperm will travel to the waiting egg, or, more rarely, the egg can descend into the uterus and be fertilized. Sterilization does not protect against STDs.

Remember that for both men and women, sterilization should be considered a permanent decision. Reversal is very often unsuccessful in men and [not possible ? in women]. You should only consider the prospect of sterilization if you are certain you do not want any more children.

Abstinence
Abstaining from sexual intercourse of any kind is 100% effective against pregnancy and STDs.

"Morning After" Treatment
What if your birth-control method has failed or you're not sure it was used properly? Three medications and procedures are available for preventing maturation of the fertilized egg.

• Two pills of combined hormones -- ethinyl estradiol (50 micrograms) and norgestrel progestin (0.5 mg) -- are taken as soon as possible after the sexual activity, but no later than 72 hours afterward. The same dose is given again 12 hours later.
  
  This is equivalent to two pills of Ovral or four pills of Lo-ovral, Nordette, Triphasil yellow pills or Trilevlen yellow pills, given each time.
  
  
• A high dose of ethinyl estradiol or conjugated estrogen taken daily for five days.
  
  
• Copper IUD inserted up to five to seven days after the sexual activity. This procedure is recommended only for women who have had one child and are at low risk for contracting STDs.

Abortion
Unfortunately, some women rely on abortion as a type of birth control. It is also relied on when a birth-control method has failed. Types of abortion performed depend on the length of the pregnancy.

In the first trimester (the first 12 weeks after the last menstrual period), the most-used procedure is vacuum aspiration, in which a suction instrument removes the embryo or fetus and the placenta.

RU 486, an abortion-inducing pill, is used during the first six weeks after the last menstrual period. This treatment is not generally available in the United States, but is fully available in France, the United Kingdom and some other nations.

In the second trimester several procedures are used.

If the pregnancy is already 13-16 weeks, dilation and evacuation can be used. This procedure is similar to vacuum aspiration.

If the pregnancy is 16-24 weeks, the more commonly done procedure is induction of labor by injection of a fluid -- salt (saline) solution or prostaglandin hormones -- into the amniotic sac. Hysterotomy (incision into the uterus) and in extreme cases, hysterectomy can also be performed.

Abortion SHOULD NOT be considered a form of birth control. It is an invasive procedure which, sometimes years later, may have serious emotional and physical repercussions, including sterility. It is not to be taken lightly.