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Pearl Index: Birth Control Effectiveness, Contraception Methods

Pearl Index


The issue of contraception is equally critical for couples who do not want to have a child soon and for couples who consciously plan parenthood. If everything is clear with the former, then the need for contraception in the latter is puzzling.

Why protect yourself if you need a baby? Responsible people should comprehensively examine their reproductive health, treat chronic diseases, eliminate chronic infections and take vaccinations. 

It is extremely important to avoid conception during this period since some medications can have a sharply negative effect on the fetus if fertilization does occur.

The Pearl Index is an indicator that characterizes the chosen contraceptive method’s reliability. It is on him that a couple should be guided in choosing a method of protection from unwanted pregnancy. Its value indicates the likelihood of an unplanned pregnancy when using a particular contraceptive method.

The concept of the Pearl index

The Pearl Index is a numerical indicator that reflects the number of pregnancies in 100 women who continuously use one or another method of contraception during the year. It is named after its creator, the American scientist Raymond Pearl. 

How to calculate it Pearl index?

If the Pearl Index is 5, then this means that out of 100 women who were protected from unwanted pregnancy for 12 months in a strictly defined way (for example, with the help of coitus interruptus), 5 became pregnant. That is, 5 women out of 100 were pregnant.

The higher the Pearl index, the less reliable this contraceptive is. Conversely, the lower it is, the lower the risk of unwanted pregnancy.

It is very important to understand here that we are only considering cases of correct use of the contraceptive method. That is:

  1. When using tablet forms of hormonal contraceptives, the rules of admission reflected in the recommendations are not violated.
  2. If we are talking about coils, they are installed only by specialists in a clinic, their validity period does not exceed the recommended one, and after their expiration, the coils are immediately removed.
  3. When using a condom, it is put on before the onset of sexual intercourse and not before ejaculation since with this option. There is a high probability that the spermatozoa contained in the lubricant will enter the woman’s genital tract.
  4. If we are talking about the calendar or temperature method, menstruation dates are accurately recorded, and temperature measurements are made with a working thermometer.

If the contraceptive method is used incorrectly, then it is obvious that the Pearl index can increase many times over.

Pearl index for different contraceptives

Pearl index Contraception methods
Contraception methods

Now let’s look at contraceptive methods and the Pearl index for each of them. All methods of protection against unwanted pregnancy can be divided into 3 large groups:

  • Biological.
  • Barrier.
  • Hormonal.

Let’s study each group in detail.

Biological methods of contraception

These methods do not imply any means of protection from the outside – only knowledge of the aspects of your body.

Calendar method

Pearl index – up to 25

It is based on clearly managing the menstruation calendar and determining favorable and unfavorable days for conception. The first 10 and the last 8-10 days of the menstrual cycle are considered relatively safe, provided a stable 28-day cycle. 4 days before and 4 days after ovulation (usually on day 14), the probability of pregnancy rises sharply – the so-called fertile window opens.

The method is very unreliable since many external and internal causes (climate change, heavy workloads, illnesses, stresses, and so on) can affect the duration of the cycle.

Billings Ovulation Method, cervical mucus method

Pearl index – about 5

Based on the measurement of basal temperature and the study of the state of cervical mucus. The day before ovulation, the basal temperature decreases slightly, and during ovulation, it rises by 0.3-0.6 degrees. As for the state of the cervical mucus, the ovulatory period is characterized by abundant glassy transparent or white secretions, which are not characteristic of the beginning or end of the cycle.

Withdrawal method, Coitus interruptus

Pearl index – from 5 to 25

Based on the extraction of the penis from the vagina before ejaculation. Control over proper execution is completely entrusted to the man, but even with his correct actions, there is a high probability of sperm in the sperm lubricant.

Lactation Amenorrhea Method (LAM)

Pearl index – up to 3

It is based on the suppression of menstruation and ovulation by the hormone prolactin, which is actively synthesized during breastfeeding. This method works only when the baby does not receive any food and drinks other than breast milk, and the breaks between feedings are no more than 3 hours. If these conditions are not met, there is a high probability that the prolactin level will be insufficient to suppress ovulation, and pregnancy will still occur.

It is important to understand that with breastfeeding, the absence of menstruation does not automatically mean the absence of ovulation, so pregnancy can occur even in the absence of menstruation.

Before introducing complementary foods, this method can be considered relatively effective for the first six months of a child’s life.

Thus, it becomes clear that biological methods of contraception often fail.

Barrier methods of contraception

These include condoms and uterine caps, which create a mechanical barrier to spermatozoa.

Condoms Contraception method


Pearl index – 2, but if used incorrectly then it increases to 18

The only method that protects from unwanted pregnancy and sexually transmitted diseases. To avoid being disappointed in this contraceptive method, it is important to use it correctly. Namely, put on a condom before the onset of sexual intercourse since live spermatozoa and pathogens of infectious diseases can be in the sperm lubricant. Even superficial contact of an unprotected penis with the external genitalia of a healthy woman of reproductive age may be enough to conceive.

Cervical cap/ FemCap

Pearl index – up to 20

The product is similar to condoms. It is put on before sexual intercourse on the cervix, blocking its entrance while maintaining the likelihood of its incorrect location.

Non-hormonal coil (IUD)

Pearl Index – 0.8-1.9

Standing apart in this group of contraceptives is the intrauterine non-hormonal coil. It cannot be called a barrier method in the full sense of the word since it does not create obstacles in the way of spermatozoa. 

Still, its contraceptive effect is also based on forming a mechanical obstacle.

Correctly inserted into the uterus, the coil prevents the fertilized egg from attaching to the endometrium, and the onset of a biological pregnancy becomes impossible.

In addition, the metal that covers the helix changes the pH of the uterine environment and makes it unviable for most spermatozoa. The unambiguous advantages of the coil include ease of use (installed once every few years) and a high contraceptive effect.

Hormonal methods of contraception

These methods of protection against unwanted pregnancy are considered the most reliable when used correctly. The method uses drugs containing analogs of female sex hormones in various combinations. They suppress ovulation and change the consistency of cervical mucus, making it impossible for sperm to pass through the cervix.

Hormonal contraceptives are available in the following forms:

  • Pills (oral contraception).
  • Skin patches.
  • Injections.
  • Hormonal intrauterine device.

Each woman can choose the most suitable one for herself.

Combined hormonal contraceptives and preparations contain only progestin (without estrogen). The latter are recommended for nursing mothers and women with contraindications to taking combined drugs (women who cannot tolerate estrogens).

The Pearl Index of all hormonal contraceptives is less than 1 if used correctly.

The greatest number of failures is possible when taking pills (oral contraceptives), as they require accuracy and care. Missed pills or diseases accompanied by vomiting can significantly increase the risk of an unwanted pregnancy.

The most convenient in this regard is the hormonal coil. A gynecologist installs it for 5 years at once, so a woman does not need to be in constant tension, as when taking pills.

Patches and injections also have a fairly long duration of action – usually several months. This is more convenient than pills but more troublesome than the hormonal coil.

Hormonal contraception is often the choice of women who have sex exclusively with one sexual partner, as they protect against unwanted pregnancy well and do not protect against sexually transmitted diseases (STDs).

For women who do not have a permanent sexual partner, barrier methods of contraception, known as condoms, are unambiguously recommended. It is good if, in addition to them, hormonal contraceptives are also present – this will give the woman additional protection and the opportunity not to worry about her future reproductive health.