Hormones and their effects
Natural effect of hormones
The hypothalamus in the brain and the pituitary gland control the hormone production that is responsible for the processes of the menstrual cycle. They make sure that the ovaries produce estrogens (female sex hormones) during the first phase of the cycle. Several ova ripen under the influence of estrogen, although usually only one ovum (egg) matures fully. Estrogens also stimulate the thickening of the uterine lining, so that if it were to be fertilized, an ovum could be implanted.
After the mature ovum has migrated from the ovary to the opening of the Fallopian tube, the protective layer (follicle) surrounding it bursts. The empty follicle is now transformed into the so-called corpus luteum (yellow body). Three to four days later, the corpus luteum starts producing the sex hormone progesterone. The synthetically produced hormone that acts like progesterone and is also contained in the Pill belongs to a class of hormones called progestins. Progesterone, too, influences the uterus in its preparation for the implantation of a fertilized ovum. If the ovum is not fertilized, the corpus luteum dries out and stops producing hormones. This reduces the hormone levels in the blood, with the result that the thickened uterine lining detaches itself and is shed with the onset of menstrual bleeding. The hormone-controlled cycle starts again.
Hormonal effects caused by the combined pill
The most common form of the Pill contains a combination of synthetically produced estrogen and progestin ("combined pill"). The only exception is the so-called minipill, which consists of progestin only. Although the various kinds of combined pill differ in their dosage and composition, their basic modes of action are comparable.
The hormonal substances in the combined pill have several effects in the course of the cycle. The hormones introduced into the body with the combined pill fool the hypothalamus into 'thinking' that the body is pregnant, whereupon it reduces its own hormone production. Maturation of the ovum and ovulation are suppressed – and in turn estrogen production in the ovaries is reduced. Furthermore, progestins ensure that the formation of mucus in the neck of the womb is stimulated, forming a natural barrier to sperm. In turn, the addition of a synthetic estrogen supports estrogen-dependent functions such as cycle stability.
Reliability
The Pearl Index has become established as a way of comparing the reliability of different contraception methods. It states in statistical terms the number of women who have become pregnant despite using a certain method of contraception over a twelve-month period. For example, the Pearl Index for contraception using condoms is between 2 and 12, meaning that out of every 100 women who only use condoms for contraception over twelve months between two and twelve become pregnant. Typical figures for the combined pill, by contrast, lie between 0.1 and 1.0 if the possibility of intake errors is taken into account. One reason for the variation between the two figures is that a woman can become pregnant as a result of usage or intake errors – e.g. forgetting to take the Pill.
The Pearl Indices of all currently available contraceptive methods show that the combined pill is one of the most reliable methods. It is also easily reversible, i.e. a woman's ability to conceive returns quickly after she stops taking it. This is not the case with other very reliable methods, such as sterilization. As with all methods of contraception, however, when taking the Pill it is crucial to avoid usage and intake errors. The package insert contains information on what action must be taken if a pill is missed. Any unanswered questions should be discussed with a physician.
Manufacturers recommend that women should also be careful if they suffer from diarrhea or vomiting within three to four hours after taking the Pill, since in such a case it cannot be guaranteed that the active ingredients will have already been absorbed by the body. Women should therefore use non-hormonal contraceptive methods in addition until they start taking the next cycle of pills.
Furthermore, certain medications, such as antibiotics or psychopharmaceuticals, can affect the Pill's efficacy. The prescribing physician can inform you about possible interactions.
No protection against sexually transmitted diseases
It is important to know that the Pill does not provide any protection against sexually transmitted diseases such as AIDS or venereal diseases. In case of doubt, you should definitely also use a condom for contraception.
The combined pill
Click here for more information about the combined pill.
