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a) Using Fertility Indicators?
Yes. If the couple uses fertility indicators (such as cervical mucus and basal body temperature [BBT]) to identify the fertile time, then ovulation can be predicted and detected despite irregular menstrual cycles. Past cycle lengths do not influence the length of abstinence in the current cycle.
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a) Women with irregular menstrual cycles can still ovulate and be fertile. The fertile period in such women can only be identified by prospective NFP methods such as cervical mucus and BBT. In the presence of irregular cycles, the period of abstinence may be excessively long and unacceptable to some couples.
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b) Using a Calendar method based on a formula?
For a woman with very irregular cycles, a calendar method based on a formula to predict the fertile time may be unacceptable due to the prolonged abstinence required.
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b) In the absence of relatively regular cycles, it is impossible for a woman to predict the fertile days in her current cycle using the calendar method. As cycle length variation increases, the number of days of abstinence increases. The most common "rule" used to predict the fertile time using a formula is subtracting a certain number of days from the shortest cycle (usually subtract 18 to 20 days) and longest cycle (usually subtract eight to 10 days) lengths in the past 6 to 12 months. If, for example, the longest cycle is 45 days and the shortest cycle is 20 days, a couple would have to abstain for more than 30 days in the woman's current cycle.
(NOTE: Cycle length is determined by starting to count on Day 1 of menses, and counting forward until the day before the next menses begins.)
Prolonged abstinence may lead to increased risk taking, and greater risk of pregnancy if intercourse occurs during the fertile time.
- Lamprecht V, Grummer-Strawn L. Development of new formulas to identify the fertile time of the menstrual cycle. Contraception 1996;54(6):339-43.
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c) Using a Calendar method based on a "blanket" rule?
Couples using a "blanket" (calendar) rule may be at increased risk for pregnancy if the woman has a very short or very long cycle.
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c) When the fertile time is predicted using a "blanket" rule - in which a set number of days each cycle is identified as the fertile time - the length of abstinence is not increased if the woman has irregular cycles. An example of a "blanket" rule is if all couples abstain starting on Day 8 of the woman's cycle and resume vaginal intercourse on Day 21. Couples using this rule would abstain for 13 days each cycle, regardless of whether the woman has irregular cycles. However, in the presence of long and irregular cycles, it is very likely that the couple will have intercourse on a fertile day as ovulation usually occurs around two weeks before the next menstruation. Thus a woman with a 39 day cycle would resume intercourse on day 21 and probably ovulate around day 25.
- Lamprecht V, Grummer-Strawn L. Development of new formulas to identify the fertile time of the menstrual cycle. Contraception 1996;54(6):339-43.
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