According to the more dominant interpretations of the doctrine or dogma of the Catholic Church, birth control is not completely forbidden. For as long as the method chosen does not impede, block, or alter natural human physiological processes, then the chosen form of birth control is perfectly acceptable. This means that things like condoms, the pill, herbal tinctures, and vasectomies are all out the window for the average, devout Catholic couple.
However, while the afore-cited methods effectively removes all of the more conventional (and some of the more unusual) forms of birth control that are publicly known, it does not eliminate something known as “natural family planning” or NFP. Incidentally, NFP techniques are “officially” supported by the Catholic Church, so there is technically no violation of dogma by using them. This, of course, is only the general consensus and may be challenged, depending on interpretation of the appropriate scriptures and teachings.
One trait that all NFP birth control tactics use is observation of the female. Working on the assumption that the male is generally fertile at all times and, thus, nothing can be done about that, NFP focuses on reading the signs of the female body. Science and ancient lore has shown that the physiology of the female body gives off certain signs during periods of fertility and infertility. According to most NFP manuals, reading these signs is a relatively low-risk way of determining whether or not there is a risk of pregnancy if the couple engages in sexual activity during a particular time. Among the signs observed are body temperature and certain features of the cervical area.
Others refer to statistics and average scientific data, such as the popular Rhythm Method. These forms of NFP rely on the established cyclical nature of fertility in the female. Working on the assumption that female fertility follows a cycle that is generally similar for all women, it is therefore possible to estimate the days of low risk for pregnancy through careful observation of the cycle. However, this method is flawed because it does not adequately measure certain factors that might affect the cycle, such as whether or not the female has a regular menstrual period. It also does not make adjustments based on hormonal changes, which can also have an effect on the menstrual cycle.
The question of whether or not NFP methods actually work can be difficult to answer, for a variety of reasons. The first is that not everyone agrees on what falls under the classification of NFP and what doesn’t. For example, the rhythm method summarized above is generally seen by the public as NFP, but it is not recognized as such by the United States Conference of Catholic Bishops. It should be noted that the Catholic Bishops Conference of the Philippines not only recognizes the rhythm method, but actually has officially backed it in the past. Statistics that show the use of NFP methods tend to vary from country to country, though it has been consistently portrayed as being a relatively unpopular choice, even among Catholic populations. It is notable, though, that very little data on the use of NFP has been found in countries that are predominantly Catholic.