ScienceDaily (Feb. 21, 2007)
— Researchers have found that a method of natural family planning that
uses two indicators to identify the fertile phase in a woman's menstrual
cycle is as effective as the contraceptive pill for avoiding unplanned
pregnancies if used correctly, according to a report published online in
Europe's leading reproductive medicine journal Human Reproduction today
(21 February). [1]
The symptothermal method (STM) is a form of natural family planning
(NFP) that enables couples to identify accurately the time of the
woman's fertile phase by measuring her temperature and observing
cervical secretions. In the largest, prospective study of STM, the
researchers found that if the couples then either abstained from sex or
used a barrier method during the fertile period, the rate of unplanned
pregnancies per year was 0.4% and 0.6% respectively. Out of all the 900
women who took part in the study, including those who had unprotected
sex during their fertile period, 1.8 per 100 became unintentionally
pregnant.
The lead author of the report, Petra Frank-Herrmann, assistant
professor and managing director of the natural fertility section in the
Department of Gynaecological Endocrinology at the University of
Heidelberg, Germany, said: "For a contraceptive method to be rated as
highly efficient as the hormonal pill, there should be less than one
pregnancy per 100 women per year when the method is used correctly. The
pregnancy rate for women who used the STM method correctly in our study
was 0.4%, which can be interpreted as one pregnancy occurring per 250
women per year. Therefore, we maintain that the effectiveness of STM is
comparable to the effectiveness of modern contraceptive methods such as
oral contraceptives, and is an effective and acceptable method of family
planning."
A number of fertility awareness based (FAB) methods of family
planning have been advocated over the years, but comparisons between
different methods and studies of their effectiveness have been limited
and hampered by problems such as differences in cultural backgrounds,
different ways to measure the effectiveness of a FAB method, different
ways of classifying unintended pregnancies and other methodological
problems.
"To be able to make an informed choice when selecting a family
planning method, couples need to know the efficacy of a method when used
both perfectly and imperfectly," said Prof Frank-Herrmann. "We believe
that this is a significant prospective cohort study that clearly defines
STM and perfect and imperfect use, and which defines intended and
unintended pregnancies, classifying them according to the couples'
intentions before conception."
The researchers selected data from a cohort of 900 women who were
part of a much larger study of 1,599 women using STM, which was
conducted by the German Natural Family Planning study centre between
1985 and 2005. The 900 women provided data on 17,638 cycles to Prof
Frank-Herrmann and her colleagues.
STM identifies the beginning and end of a woman's fertile period
using two measurements (body temperature and cervical secretions) in
order to have a double-check system. The first fertile day is when the
woman first identifies either: 1) first appearance or change of
appearance of cervical secretion, or 2) the sixth day of the cycle.
After 12 cycles, this second guideline is replaced by a calculation that
subtracts seven days from the earliest day to show a temperature rise
in the preceding 12 cycles, in order to identify the first fertile day.
The woman is then in her fertile period. The fertile phase ends after
the woman has identified: 1) the evening of the third day after the
cervical secretion peak day, and 2) the evening when the woman measures
the third higher temperature reading, with all three being higher than
the previous six readings and the last one being 0.2 degrees C higher
than the previous six.
Prof Frank-Herrmann said: "The women or couples who want to learn the
method have to buy a book, or attend an NFP course, or get some
teaching by a qualified NFP teacher. Learning STM is usually no problem.
There are precise rules that work. However, in contrast to the oral
contraceptive pill or other family planning methods, STM needs more
engagement and time to learn it."
Every month the women in the study sent charts to the researchers
that showed their cycles, their observations of temperature and cervical
secretions, and that recorded their sexual behaviour and family
planning intentions for the next cycle.
Of the 900 women, 322 used only STM and 509 women used STM with
occasional barriers during the fertile time. Sixty-nine women did not
document their sexual behaviour. Out of the women who documented their
sexual behaviour and abstained from sex during their fertile period
("perfect use") the unintended pregnancy rate was 0.4 per 100 women and
13 cycles [2], and 0.6 for women who used STM plus a barrier if they had
sex during their fertile period. For cycles in which couples had
unprotected sex during the fertile phase, the pregnancy rates rose to
7.5 per 100 women and 13 cycles. The drop-out rate from using STM for
reasons such as dissatisfaction or difficulties with the method was 9.2
per 100 women and 13 cycles, and compared well with the drop-out rates
from other methods of family planning, which can be as high as 30%,
although direct comparisons are difficult due to methodological
problems. "This demonstrates a fairly good acceptability for this
particular FAB method," said Prof Frank-Herrmann.
The authors were surprised by the relatively low rate of unintended
pregnancies (7.5%) among women who had unprotected sex during their
fertile period. "If people are trying for pregnancy you expect a
pregnancy rate of 28% per cycle," said Prof Frank-Herrmann. "Therefore,
we think that some of the couples were practising conscious, intelligent
risk-taking, and were having no unprotected sex during the few highly
fertile days, but had unprotected intercourse on the days at the margins
of the fertile time when the risk of pregnancy was lower."
Some studies have suggested that women's libido is higher during
their fertile period, and this could be one of the reasons why NFP
methods traditionally have had a reputation for being less effective
than other methods of family planning. However, Prof Frank-Herrmann
said: "There are studies that suggest that this is only the case for a
small proportion of women, and that, in fact, women also identify other
parts of their cycle with increased sexual desire. Most women who use
FAB do not find this a problem. It's possible that the increased libido
may be one of the reasons that some of the couples in our study used a
barrier, such as a condom, in the fertile phase.
"This is the first time that a large, prospective STM database has
been established with sufficient detailed information on sexual
behaviour. It enables the true method effectiveness for STM to be
calculated and we found this was 0.4% per year when there was no
intercourse during the fertile phase. The user-effectiveness of STM, in
other words the total number of unintended pregnancies that were due to
both method and user failure, was 1.8% after 13 cycles of use, and this
compares very well with results from other European studies of FAB
methods of family planning. The markedly good user-effectiveness rate
may be explained partly by the motivation of the couples and their
teachers who agreed to participate in the study," she concluded.
[1] The effectiveness of a fertility awareness based method to avoid
pregnancy in relation to a couple's sexual behaviour during the fertile
time: a prospective longitudinal study. Human Reproduction.
doi:10.1093/humrep/dem003. [2] This assumes a woman has 13 cycles in a
year.
Editor's Note: This article is not intended to provide medical advice, diagnosis or treatment.
Story Source: The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by European Society for Human Reproduction and Embryology. European Society for Human Reproduction and Embryology (2007, February
21). Natural Family Planning Method As Effective As Contraceptive Pill,
New Research Finds. ScienceDaily.
Источник: http://www.sciencedaily.com/releases/2007/02/070221065200.htm |