These misconceptions arise from a lack of understanding of the physiology of the menstrual cycle. Four hormones control the menstrual cycle. They are follicle stimulating hormone (FSH), estrogen, luteinizing hormone (LH), and progesterone. The delicate balance of these hormones in the blood regulates the sequence of events leading to ovulation and, if the egg is not fertilized, menstruation. Menstruation occurs at more or less regular intervals (monthly) although there are great variations in cycle length between women and also variations in the same woman at different times in her life due to age, stress, and other factors.
Since the egg can be fertilized for approximately 12-24 hours after ovulation (perhaps more) and sperm maintain their capacity to fertilize the egg for up to 48 hours after ejaculation, an unsafe period of at least 3 days occurs at the time of ovulation - 2 days prior to ovulation and 1 day after.
The next problem is to pinpoint the time of ovulation. It is possible to do this with a reasonable degree of accuracy, given sufficient motivation and intelligence. It requires the daily recording and interpretation of body temperature, by noting the appearance of certain physical symptoms (which don't appear in some women), and by a prediction of the time of ovulation based on the length of previous menstrual cycles.
In summary, fertilization can occur only around the time of ovulation. Ovulation occurs in response to changes in the hormonal balance regulating the menstrual cycle. The hormonal balance itself is easily affected by external factors. Therefore, ovulation doesn't necessarily occur "towards the end of the menstrual cycle" or "on the 14th day of the cycle" or "during a menstrual period" etc., although it may occur then. There is no way of predicting the exact time, and the best estimates are often in error.
"Rhythm methods are not effective."
The rhythm methods of birth control are effective in certain cases.
To use rhythm effectively, couples are required to have sufficient intelligence, motivation and self-discipline to restrict intercourse to the defined "safe period" of each menstrual cycle. The most effective use of rhythm does entail a failure rate and the definition of the "safe period" of each cycle varies according to which method is used.
The calendar rhythm method is the least effective of the three rhythm methods. Estimating when ovulation will occur in the present menstrual cycle solely by basing the calculations on the length of past menstrual cycles is unsatisfactory. Each cycle is subject to variations caused by a number of external factors not related to the length of previous cycles. In addition, if the woman's cycles vary in length by 10 or more days the method is impractical. According to the World Health Organization (WHO), the calendar rhythm method has a failure rate of 14 to 40 per hundred woman-years.
The most effective rhythm method is the basal body temperature (BBT) method. The strict application of BBT is associated with a failure rate of 0.8 to 1.4 per 100 woman-years (WHO figures). Combining observation of certain physical symptoms of ovulation with daily temperature records is called the "sympto-thermal" method. Another variation, the "Billings method", determines the time of ovulation by observing changes in the cervical mucus during a woman's cycle. These methods are not acceptable to many couples because they restrict intercourse to the post ovulatory safe time.
The third method is a combination of BBT and calendar rhythm. Calendar calculations are used to determine the approximate beginning of the pre-ovulatory unsafe time and BBT helps to determine the beginning of the post-ovulatory safe time. It is associated with a failure rate of 3.2 to 8.0 per 100 woman-years (WHO figures).
As is readily apparent, the lowest pregnancy rates are obtainable only by intelligent, highly-motivated couples. Failures occur because of variations in length of the menstrual cycle, misunderstanding of the method, and/or unwillingness to abstain from intercourse during the unsafe time.
"A woman ovulates twice or more during her cycle and at different times."
"A woman ovulates each time she has intercourse."
A woman can ovulate more than once per cycle (as in cases of fraternal twins) but this will usually occur within the same 24 hour period. Hormones regulating the menstrual cycle suppress ovulation at other times.
Intercourse does not induce ovulation since it does not change the natural progression of the woman's hormonal cycle. Some doctors, however, claim that intercourse will induce ovulation especially in very young women. This is difficult to substantiate and, in any event, rhythm methods of birth control cannot be recommended for young women whose menstrual cycles are still irregular and not well established.
"An increase in vaginal mucus discharge signifies the onset of the safe period."
Increases in vaginal mucus discharge generally have nothing to do with fertility. The nature of vaginal mucus changes and the quantity increases during normal sexual excitement and in cases of inflammation and infection.
The changes associated with ovulation occur in the cervical, not vaginal, mucus. For most of the menstrual cycle, the cervical mucus is thick, scant and impenetrable to sperm. During the four to five days around the time of ovulation, the mucus changes to become copious, watery, thin and readily penetrable to sperm. This change in cervical mucus is usually not apparent to the woman and so cannot be relied upon to ascertain the time of ovulation and the subsequent "safe period".
A method of detecting changes in cervical mucus signifying ovulation is presently being studied. Liquification of the cervical mucus liberates quantities of sugar previously bound up in the solid state. A tape has been developed which changes colour on contact with sugar. This method has certain drawbacks. One is that it is difficult to test the cervical mucus without contamination by the surrounding vaginal secretions, which, itself, may show typical "sugar changes".
Used with permission from Health and Welfare Canada
Myths and Misconceptions about Birth
ControlHealth Sexuality