The Effectiveness Of Natural Family Planning
by John Kippley
Part 2 — METHOD EFFECTIVENESS
Part 1: Introduction: The Effectiveness of NFP
Part 2: Method Effectiveness
Part 3: User Effectiveness
Part 4: The Ethics of FDA and ACOG Regarding NFP
Part 5: References
The Los Angeles Study
100% Method Effectiveness
Between 1976 and 1978, the U.S. Department of Health, Education, and Welfare conducted a prospective study to determine the relative user effectiveness of two different systems of Natural Family Planning.1 Participants were randomly assigned to either the Sympto-Thermal Method (STM) or Ovulation Method (OM) sides of the study. However, they were first screened to eliminate any couples who had a serious health, economic, or social reason to avoid pregnancy. The resulting group of 1257 couples had an average age of 28 and had only one child per family.
In the STM side of the Los Angeles study, couples determined the end of Phase I by using a calculation based on the woman's previous cycle history (short cycle minus 21 equals the last day of Phase I) and cross-checked that with the continued absence of mucus. They determined the start of Phase III by cross-checking three days of well elevated temperatures with four days of the disappearance of the cervical mucus which characterizes the fertile time.
The couples who followed these simple rules achieved a 100% effectiveness rate in avoiding pregnancy, i.e., zero unplanned pregnancies. (The couples who used the OM rules had 5.67 unplanned pregnancies per 100 woman years of exposure, i.e., about a 94% method effectiveness rate. Better OM results were achieved in a five nation World Health Organization study: a standard Pearl rate of 2.6; i.e. a 97.4% effectiveness rate.)2
A 100% effectiveness rate cannot be sustained in a large population and thus claims made for the STM state "99% method effectiveness."
The Fairfield Study
99% Method Effectiveness
Between 1970 and 1972, 1022 couples participated in a five nation (Canada, Colombia, France, Mauritius, U.S.A.) study called the Fairfield Study after the university of the principal investigator.3 The calculation used to determine the end of Phase I (short cycle minus 19 or 20) was more liberal than that used in the later Los Angeles Study; a three day temperature-only rule was used to determine the start of Phase III without cross-checking for the disappearance of cervical mucus. The couples who followed these more liberal rules achieved a method effectiveness rate of 99% according to the Pearl formula (9 unplanned pregnancies in 14,416 months of exposure).
The Roetzer Studies
99% and 100% Method Effectiveness
Dr. Roetzer has distinguished between the method effectiveness of Phase I and Phase II according to his rules.4 In his 1978 study, he reported that coitus during the first six days of the fertility/menstrual cycle yielded one pregnancy in 8,532 cycles, a Pearl rate of less than 0.2 per 100 woman years of exposure, i.e., well within a 99% effectiveness. Using a combination of three days of well elevated temperatures cross-checked by three days of the disappearance of more fertile mucus to determine the start of Phase III, couples experienced zero unplanned pregnancies in 17,000 cycles, i.e. a 100% method effectiveness rate.
The Doring Temperature-Only Study
99% and 100% Method Effectiveness
Dr. Gerhardt K. Doring tested the only pure temperature-only system reported in the literature--using a temperature based calculation for determining the end of Phase I as well as the start of Phase III.5 With the formula "earliest day (in previous cycles) of thermal shift minus 7 yields the last day of Phase I," there were 13 unplanned pregnancies among 37,035 cycles, a Pearl rate of 0.42 per 100 woman years, well within the 99% level of effectiveness. Among 307 couples using a three day very strong thermal shift pattern for the start of Phase III and confining intercourse only to Phase III, there were zero unplanned pregnancies in 11,352 cycles, another 100% method effectiveness rate with a limited population.
The Vincent Study
99% Method Effectiveness
Similar results were achieved in a French study published in 1967.6 Couples in this study had intercourse only in Phase III as determined by a rule similar to that of Dr. Doring., There was one unplanned pregnancy in 17,500 cycles yielding a Pearl rate of 0.07 per 100 woman years of exposure, well within the 99% level of effectiveness.
Conclusion 1. Studies conducted in Canada, Colombia, France, Germany, Mauritius and the United States have demonstrated a 99% method effectiveness for the Sympto-Thermal and Temperature-Only Methods. These studies were conducted under a variety of conditions and demonstrate beyond any reasonable question of a doubt that this extremely high effectiveness can be achieved by ordinary couples who receive adequate instruction and follow the relatively simple rules of these methods.
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