This is the most accurate of thes; as the name implies it combines the temperature and the mucus methods. This means that the user gains the benefits of each; ideally she can recognize when ovulation is approaching by observing changes in her mucus and external os, and can also determine that ovulation has taken place by taking her temperature. This also means combining the disciplines of both methods; she must take her BBT every day, and also examine her mucus several times every day for the unsafe period.
For accuracy in interpretation, the temperature must be charted along with the quality, quantity and appearance of the vaginal mucus, position and appearance of the external os, midpain, spotting (slight bleeding at the time of ovulation), and menstrual bleeding. The greater the woman’s diligence in observing and plotting these factors accurately, the safer the method.
Of all the methods of, the s suffer most from the discrepancy between the theoretical failure rate and the actual failure rate. This is directly related to the complexity of the method. If a woman just has to take a pill every day and nothing else she is fairly unlikely to get the process wrong (although it does happen), but the more detail and interpretation that is necessary for a contraceptive method the more chance there is for human error. This can work against the efficiency of the rhythm methods.
Ironically it is the mucus method, theoretically the most accurate of the three basic rhythm methods, which has the greatest discrepancy between theoretical rate and actual rate, because it is more complex and women find it more difficult to interpret the signs. Although the theoretical failure rate is only 2 per 100 women in a year, the actual failure rate is 25— one in four women become pregnant over a year. The calendar method, which is known to be hit-and-miss, has a theoretical failure rate of 13 per 100 women in a year; in fact the actual rate is 21 — lower than that of the mucus method! The temperature method has a theoretical failure rate of 7 per 100 women in a year, with an actual rate of 20 — making all three methods much of a muchness.
Themethod poses some controversy over failure rates. When Ingrid Trobisch’s book The Joy of Being a Woman was published it gave this method’s failure rate as up to 0.7% — less than it gave to the pill! This seems optimistic by any standards. In An Experience of Love, in answer to a charge of exaggeration on this point, Dr Roetzer (who pioneered this method) remarks that he feels this is accurate provided that all the detailed principles he lays down are observed. These take the form of rules regarding where the temperature rise occurs, its extent, and its relationship to changes in the cervical mucus. The Which? Guide to Birth Control states that: ‘The most reliable study comparing the cervical mucus method with the method suggested very little difference in pregnancy rates, which were around 20-24 per 100 women in a year.’ It then goes on to say that ‘some very enthusiastic users claim much better results’.
There is certainly an enormous discrepancy in these suggested failure rates, but one conclusion does seem to arise from all the discussions of the sympto-thermal method. Basically, the more dedicated you are to the method and the more conscientious your observations, then the lower your chances of becoming pregnant.
Advantages and disadvantages
All rhythm methods have several advantages in common. None of them uses anything hormonal or chemical, and none of them uses anything mechanical at the time of intercourse. Both partners can be fully involved in implementing the method together, and for some couples this can lead to a deepening of their commitment. No previous preparations are needed for sex on the ‘safe’ days, and some couples also find that the ‘unsafe’ times encourage them to develop other ways of showing their love for one another. No medical complications or side effects occur to either partner except in some cases of accidental pregnancy. Used rigorously, the sympto-thermal method in particular has an acceptably high theoretical success rate. There are no problems with re-establishing fertility after using this method.
Some of the disadvantages are also common to all the methods. The woman’s cycles have to be plotted for at least six months before the method begins (a year for the calendar method) so that she can learn to interpret them correctly. The most obvious disadvantage is that the couple have to abstain from sex for a certain time every month, which can be more than a fortnight in some cases. The longest periods of abstention are required by the calendar method. Some couples, or individual partners, find the required abstention ethically, emotionally or practically undesirable or unacceptable. All of the methods can be upset by illness, tiredness or. None of the methods is good for couples where one partner is away for long periods, for instance in the forces, as they may find that the time when they are together is ‘unsafe’. The main potential risks of the method occur with unplanned pregnancies, where in some cases the pregnancy can be endangered or the child damaged.
It is often easy to say definitely that ovulation has taken place in a woman’s menstrual cycle. The more factors that are observed, the more definitely this can be said, taking into account midpain, mucus changes, alterations in the position and appearance of the external os, temperature
changes, and spotting. It is then easy to avoid sex for a few days. What is not so easy is predicting when ovulation is going to take place, and avoiding sex for four days before that time. Research in rhythm methods is constantly trying to find a way of predicting ovulation; if this can be found, the time of abstinence would be reduced and might make the rhythm methods more acceptable and more accurate for more couples.