3 Artificial contraception

3.4 Natural methods of contraception

Many people with particular religious beliefs are fundamentally opposed to the use of artificial methods of contraception. In the developing world, where, as you saw above, the population is frequently increasing at an unsustainable rate, this is a particular problem. For Muslims and Roman Catholics (and others), who may nonetheless wish to limit their families, the preferred option is to use natural family planning methods. The most commonplace method, which involves estimating the ‘fertile period’ (the time when sperm and egg could meet and result in a pregnancy) from the date of the last menstrual period, only stands a chance of working if the woman has regular menstrual periods. Many women do not, so this method is extremely unreliable. Indeed, in a very short menstrual cycle, it is possible that ovulation may occur immediately after menstruation, and so, because sperm can live for up to five days inside a woman, intercourse within five days of this time – from the start of menstruation – is risky. Other natural methods are based on a close observation of the physical changes that women experience throughout their menstrual cycles, and avoidance of intercourse during the fertile period. In particular, two parameters are most often used: body temperature, and the consistency of mucus secreted from the cervix.

A woman's body temperature rises just after ovulation, and remains elevated for three days. The egg will live for only about two days, so the third day of high temperature marks the end of the fertile period. However, it is not true to say that the beginning of the high-temperature phase corresponds with the start of the fertile period; because of sperm survival, intercourse on any of the five days preceding ovulation might result in pregnancy. Again, because this method cannot pinpoint the start of the fertile period, it is necessary to abstain from intercourse from the First day of menstruation, and resume only after the end of the fertile period. This effectively rules out intercourse for more than half the woman's menstrual cycle. It is also prone to error since other factors, such as illness and some drugs, can also raise body temperature.

The other common natural method of contraception, the cervical mucus method, relies on the fact that the cervical mucus changes in consistency before ovulation. Cervical mucus is one of the body's natural defences, as it helps to prevent infection by presenting a thick, sticky barrier which pathogens cannot easily cross (see Section 3.1). For most of the menstrual cycle the mucus is present in only small amounts, but is very viscous. However, about five days before ovulation, more is produced, and it is ‘wetter’ and more slippery.

Q Can you suggest what the advantage of this might be?

A It will be easier for sperm to penetrate into the uterus and Fallopian tubes at a time when an egg might be there to be fertilized.

The change in cervical mucus therefore defines the start of the fertile period. However, once again the method is not foolproof, and many women find it difficult to distinguish between ‘wet’ and ‘dry’ days.

In contrast to the artificial contraceptive methods mentioned above, which are all fairly easy to use, natural methods require very careful observation, counselling and instruction by a trained practitioner, and are generally not very suitable for many women who have irregular cycles or naturally variable cervical mucus. Failure rates are high: as many as 20% of women using these methods will become pregnant each year. There are no side-effects caused by physical intervention, although the requirement to be aware of one's body temperature can sometimes take away the spontaneity of a sexual encounter.

However, new techniques are on the horizon. If you look at Figure 7, you will see that another hormone, luteinizing hormone (LH) has a production pattern that varies throughout the menstrual cycle. (LH is made by the pituitary gland, a part of the brain.) The interesting thing about this hormone is the peak it shows around the time of ovulation. Recently a test has been produced to monitor LH levels in urine, and give a colour change when levels are rising or high. By avoiding intercourse on the ‘high LH’ days, it is believed that fertilization can be avoided. There is not yet any evidence to suggest how effective this test is, although the technology it uses – which space prevents us from discussing here – suggests that it will be very sensitive.

Figure 7, Pattern of production of luteinizing hormone (LH) through the menstrual cycle. The downward-pointing arrow denotes the time of ovulation.

The choice of whether or not to practise contraception, and if so, which method to adopt, is a complex one. There are physical and emotional advantages and drawbacks to all the methods; religious, economic and cultural pressures also play a very important part in the decision. Most individuals will have to make some kind of choice about the matter at some time in their lives, however, so it is important that the relevant information be freely available to all who need it. In this country there is widespread availability of family planning clinics, which are a good source of advice about suitable methods for particular individuals.