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Effectiveness
of Natural Family Planning Methods
University of Heidelberg Study (published February 2007)
99.6% Method Effectiveness
This study involving 900 women, who were
observed over a 20 year period (1985-2005),
was published in the journal, Human
Reproduction, and found that the correct
use of the Sympto-Thermal Method (STM) to
postpone pregnancy led to a rate of 0.4
pregnancies per 100 women per year. The
lowest pregnancy rate was found among women
who abstained from sex during their most
fertile period identified through STM.
In contrast, women who used STM but (in
violation of Church teaching) used a barrier
method, such as a condom, during their
fertile period (instead of abstaining) had a
higher pregnancy rate (.6 pregnancies per
100 women per year).
In addition, the study found that women
who had sex (without contraception) during
the fertile period had a pregnancy rate of
only 7.5 pregnancies per 100 women per year,
which researchers noted was a quarter of the
rate one would usually expect. They
attributed this statistic to the greater
awareness couples practicing STM have of
their personal fertility cycle.
British Medical Journal Study
99.8% Method Effectiveness
The largest natural family planning study
combined effective teaching with high
motivation and showed that natural family
planning can be extremely effective in the
Third World. The study was of 19,843
pre-dominantly poor women in Calcutta, 52%
Hindu, 27% Muslim, and 21% Christian.
Because of poverty motivation was high both
among the users and among the well trained
teachers of natural family planning. The
failure rate was similar to that with the
combined contraceptive pill - 0.2
pregnancy/100 women users yearly.
The World Health Organization Study
99.996% Method Effectiveness
A total of 869 women of proved fertility
and widely varying cultural, educational,
and economic backgrounds were studied in
five centers (Auckland, Bangalore, Dublin,
Manila, and San Miguel, El Salvador).
Regardless of culture and education, 93% of
the women recorded an interpretable
ovulatory mucus pattern. Of the El Salvador
women, 48.1% were illiterate and yet
recognized the mucus symptoms.
Detailed analysis in the WHO study
confirmed the effectiveness of mucus symptom
observation as a means of family planning.
The probability of conception from
intercourse outside the period of fertility
defined by cervical mucus observation was
0.004. Intercourse on days designated as
fertile by cervical mucus observation
resulted in conception with increasing
frequency the nearer to ovulation that
intercourse occurred. Intercourse on the
peak day of cervical mucus secretion
resulted in a probability of conception of
0.667.
Thus it is clear that women of all
cultures and educational backgrounds can
learn to recognize when they ovulate and are
potentially fertile, and that if intercourse
is avoided on potentially fertile days,
pregnancies will not occur.
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.
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.)
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.
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. 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. 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. 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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