badanie_heidelberg.pdf

Human Reproduction pp. 1–10, 2007

doi:10.1093/humrep/dem003

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

P.Frank-Herrmann 1,8 † , J.Heil 2,† , C.Gnoth 3 , E.Toledo 4 , S.Baur 5 , C.Pyper 6 , E.Jenetzky 7 ,

T.Strowitzki 1 and G.Freundl 5

1 Department of Gynaecological Endocrinology and Fertility Disorders, University of Heidelberg, Voßstrasse 9, 69115 Heidelberg,

Germany, 2 Department of Obstetrics and Gynaecology, University of Heidelberg, Voßstrasse 9, 69115 Heidelberg, Germany,

3 Department of Obstetrics and Gynaecology, University of Cologne and Centre for Family Planning, Endocrinology and

Reproductive Medicine, Rheydter Straße 143, 41515 Grevenbroich, Germany, 4 Department of Preventive Medicine and Quality

Management. Hospital Virgen del Camino, C/Irunlarrea 4, E-31008 Pamplona, Spain, 5 Section Natural Fertility, German Society for

Gynaecological Endocrinology, Voßstrasse 9, 69115 Heidelberg, Germany, 6 National Perinatal Epidemiology Unit, Department

of Public Health, University of Oxford, Old Road Campus, Oxford, OX3 7LF, Great Britain and

7 Institute of Medical Biometry and

Informatics, University of Heidelberg, Im Neuenheimer Feld 305, 69120 Heidelberg, Germany

8 To whom correspondence should be addressed at: Department of Gynaecological Endocrinology and Fertility disorders, University of

Heidelberg, Voßstrasse 9, 69115 Heidelberg, Germany. E-mail: petra.frank-herrmann@med.uni-heidelberg.de

BACKGROUND: The efﬁcacy of fertility awareness based (FAB) methods of family planning is critically reviewed.

The objective was to investigate the efﬁcacy and the acceptability of the symptothermal method (STM), a FAB method

that uses two indicators of fertility, temperature and cervical secretions observation. This paper will recommend a

more suitable approach to measure the efﬁcacy. METHODS: Since 1985, an ongoing prospective observational longi-

tudinal cohort study has been conducted in Germany. Women are asked to submit their menstrual cycle charts that

record daily basal body temperature, cervical secretion observations and sexual behaviour. A cohort of 900 women

contributed 17 638 cycles that met the inclusion criteria for the effectiveness study. The overall rates of unintended

pregnancies and dropout rates have been estimated with survival curves according to the Kaplan – Meier method.

In order to estimate the true method effectiveness, the pregnancy rates have been calculated in relation to sexual beha-

viour using the ‘perfect/imperfect-use’ model of Trussell and Grummer-Strawn. RESULTS: After 13 cycles, 1.8 per

100 women of the cohort experienced an unintended pregnancy; 9.2 per 100 women dropped out because of dissatis-

faction with the method; the pregnancy rate was 0.6 per 100 women and per 13 cycles when there was no unprotected

intercourse in the fertile time. CONCLUSIONS: The STM is a highly effective family planning method, provided the

appropriate guidelines are consistently adhered to.

Key words: contraception/efﬁcacy/fertility awareness based methods/natural family planning/symptothermal method

Introduction

Background

Fertility awareness based (FAB) methods is a term that

includes all family planning methods that are based on the

identiﬁcation of the fertile time. They are based on the

woman’s observation of physiological signs of the fertile and

infertile phases of the menstrual cycle. This knowledge can

be used to plan or avoid pregnancy. FAB methods depend on

two key variables: ﬁrst the accurate identiﬁcation of the

fertile days of a woman’s menstrual cycle (the fertile time)

and second the modiﬁcation of sexual behaviour either to

plan a pregnancy or to use this knowledge to avoid pregnancy.

When couples use FAB methods of family planning to avoid

pregnancy, they practise different sexual behaviour during

the fertile time. When FAB methods involve sexual abstinence

during the fertile time, this method is called natural family

planning (NFP). When FAB methods involve occasionally

using a barrier method during the fertile time, the method is

called FAB method with barriers. It must also be recognized

that although many couples state they are practising a FAB

method, sometimes they do not adhere to the guidelines and

unprotected intercourse or other kinds of genital contact

† The ﬁrst two authors contributed equally to this work.

# The Author 2007. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology.

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P.Frank-Herrmann et al.

occur during the fertile time. The efﬁcacy of FAB methods to

avoid pregnancy has been critically reviewed by several

authors (Fehring et al., 1994; Frank-Herrmann et al., 1991;

De Leizaola-Cordonnier, 1995; Barbato and Bertolotti, 1988;

Hilgers and Stanford, 1998; Howard and Stanford, 1999;

Kambic, 1999; The European Natural Family Planning Study

Groups, 1999; Grimes et al., 2004). Several issues have been

identiﬁed when attempting to compare the different FAB

methods.

The ﬁrst is that most FAB methods have evolved concur-

rently over the last 40 years in different countries; each has

been lead by pioneers who have developed guidelines for

their respective groups. This has resulted in many cases in a

lack of evidence-based guidelines being developed and

subsequently modiﬁed to conform to best scientiﬁc evidence.

The second issue is that efﬁcacy rates may vary because they

are derived from studies done with volunteers and researchers

from different cultural backgrounds where motivation to avoid

pregnancy and rigour of research methods may vary (World

Health Organization, 1981a,b; Gomes and Congdon, 1988;

Xu et al., 1994; Indian Council of Medical Research Task

Force on Natural Family Planning 1996).

Third, the methods currently used to calculate the method

effectiveness are questionable. Many investigators have recog-

nized the importance of distinguishing between pregnancies

attributable to user failure and method failure (method effec-

tiveness). The standard procedure up to now was to compute

separate method and use-effectiveness rates (pregnancies

divided by exposure). In this procedure, all exposure from

perfect and imperfect use is included in denominator of both

method and user failure rates. The common misinterpretation

is that the resulting method effectiveness rate yields infor-

mation about the inherent efﬁcacy of the method. Inherent

method efﬁcacy can be measured only when the numerator

(method failures) is assessed in relation to the proper risk set,

i.e. the exposure only when the method is used perfectly. For

this reason, method effectiveness rates computed by the stan-

dard procedure are biased downwards to an unknown extent

(Trussell and Grummer-Strawn, 1990).

This problem is further confounded by the different ways an

unintended pregnancy is classiﬁed. Some prospective studies

ensure the couple’s intention to avoid a pregnancy is recorded

at the beginning of each menstrual cycle. Other studies are ret-

rospective and only question the couple’s intention after sexual

intercourse has been recorded during the fertile time.

The fourth issue is that some new FAB methods are simpli-

ﬁed methods that are often used in developing countries and

very relevant for settings where cost of teaching is an issue and

where continuation has a higher priority than efﬁcacy (Thapa

et al., 1990; Jennings and Sinai, 2001; Arevalo et al., 2004).

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 consistently and imperfectly. Trussell

and Grummer-Strawn are critical about how efﬁcacy has

been calculated in previous studies. They argue that previously

published rates of method and user failure for all contraceptive

methods suffer from methodological errors and are biased

downwards. Trussell and Grummer-Strawn (1990, 1991) rec-

ommend a new model of calculating perfect and imperfect

use pregnancy rates which up to now has rarely been applied.

This is likely to be due to the fact that this approach requires

documentation of all sexual behaviour during each cycle.

Description of the method

This paper describes a cohort of couples who used a method

that consisted of recording the cervical secretion pattern,

changes of basal body temperature and the application of a cal-

culation rule. It is called the symptothermal method (STM) of

NFP. The beginning and the end of the fertile time are ident-

iﬁed by two parameters in order to have double-check system.

The following two guidelines are given to each couple to

identify the ﬁrst fertile day – both guidelines are applied and

the ﬁrst fertile day is the earliest day identiﬁed (Figure 1):

(i) Change of cervical secretion: ﬁrst appearance of cervi-

cal secretion.

(ii) Calculation guideline: the ﬁrst fertile day is the sixth

day of the cycle (In NFP methodology, this is called

the ‘ﬁve days rule’ which states that the ﬁrst ﬁve

Figure 1. Determination of the fertile time according to the guidelines of the symptothermal (STM) method.

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Effectiveness of a fertility awareness-based method

days of the cycle are infertile days.) or after a woman

has completed 12 cycles of use this guideline is

replaced by a calculation that takes the earliest temp-

erature rise in the last 12 cycles and subtracts seven

days to identify the ﬁrst fertile day (In NFP method-

ology, this is called the ‘minus eight rule’: earliest

temperature rise in the last 12 cycles minus eight

days to identify the last infertile day.)

The following two guidelines are given to each couple to ident-

ify the last fertile day—both guidelines are applied and the last

fertile day is the latest day identiﬁed (Figure 1):

(i) The evening of the third day after the cervical secretion

peak day (The cervical secretion peak day is only

recognized on the day following peak, when the

secretions have become sticky again.)

(ii) The evening of third higher temperature reading, all

three higher than the previous six readings, the last

one 0.2 8 C higher than the previous six.

These evidence-based guidelines have been developed follow-

ing extensive research that has been carried out over the last 20

years. They have been adopted widely by FAB groups who

teach the STM method (Raith et al., 1999). Detailed guidelines

of the STM methodology are described elsewhere (Arbeits-

gruppe NFP, 2006).

Table I. Exclusion criteria and number of participants excluded

Category

Number

Percentage

Participants in the whole database

1599

Participants in the effectiveness study

900

Excluded

699

100

Participants excluded by reason

Pregnancy achieving at study entry

356

50.9

Post-pill

125

17.9

Irregular cycles (.35 days)

10.6

Post-partum/breastfeeding

8.5

Experienced users

4.7

Premenopausal women over 45 years

3.9

No sexual partner

1.7

Young women under 19 years

1.1

Post-abortum

0.7

NFP were excluded. The reasons for excluding the women and the

number of women excluded are given in Table I.

Inclusion criteria

The inclusion criteria are given in Table II in accordance with the

recommendations from Tietze and Lewit (1974), Trussell and Kost

(1987) and Potter (1996). A subcohort of 900 women with 17 638

cycles was selected out of the whole database.

The women had to state that they intended to avoid pregnancy and if

they changed their intention they had to be willing to let the

investigator know at once in order to have a clear deﬁnition of

unintended pregnancy (discussed later). The women had to be

willing to record all sexual behaviour, especially the occasional use

of barrier methods to ensure clarity about the deﬁnitions for perfect/

imperfect-use (discussed later). The couples must not use any contra-

ceptive methods other than barrier methods. The study speciﬁcally

only included those couples who were starting to use the STM

method and commencing the ﬁrst STM cycle. To ensure the partici-

pants were likely to have normal fertility, the women had to be

between 19 years at entry into the study and less than 46 years at

the end of the study. To ensure the women could become pregnant

(i.e. were likely to have fertile ovulations), the average cycle length

of the women had to be between 22 and 35 days (20% of the cycles

of each study participant was allowed to deviate outside this range).

Only those women with no previous history of infertility were

included. There was no requirement for proven fertility in terms of

the women already having a history of being pregnant, in order not

to exclude the younger, potentially more fertile and sexually active

women. In a previous data analysis, we found no signiﬁcant difference

in unintended pregnancy rate between those with and without proven

Objectives

Our ﬁrst objective was to analyse the overall use effectiveness

of the STM method and to determine whether the effectiveness

was different for different types of sexual behaviour during the

fertile time according to the ‘perfect/imperfect-use model’

(Trussell and Grummer-Strawn, 1990). In particular, we

speciﬁcally wanted to know if those women who only used

the STM without combining with a barrier method during the

fertile time had fewer unintended pregnancies, regarding the

use-effectiveness rates, than those women who occasionally

used barrier methods during the fertile time.

Our second objective was to investigate the acceptability of

the STM method. We therefore reviewed those couples whose

reasons for discontinuing the STM were due to dissatisfaction

with the method or due to difﬁculties with using the STM.

Materials and methods

The study was conducted by the German NFP study centre in

accordance with the ethical principles of the Declaration of Helsinki.

The study centre is an integral part of the German Society of Gynae-

cological Endocrinology and Reproductive Medicine. Its main aim is

to undertake research studies in the ﬁeld of NFP and to evaluate NFP

services. For the last 20 years, the study centre has coordinated this

prospective, observational longitudinal cohort study. Between 1985

and 2005, the study enrolled 1599 women using the STM in different

situations and collected data from 35 996 menstrual cycles. This data

set has already addressed several questions (Gnoth et al., 1999, 2002,

2003). From this data set, a cohort of 900 women with 17 638 cycles

met the effectiveness study selection criteria.

Table II. Inclusion criteria for the effectiveness study

Inclusion criteria

Age 19 – 45 years

Normal cycle lengths between 22 and 35 days (20% of cycle lengths could

be outside this range)

Willing to record family planning intention at the start of each cycle

Willing to record sexual behaviour, including sexual intercourse, genital

contact, withdrawal, occasional barrier use

Agreement not to use any other forms of contraception

No known history of subfertility or infertility

An established luteal phase of at least 10 days hyperthermic phase and at

least 3 months following breastfeeding, oral contraception, post-partum,

post-abortum

Willing to participate in the study for 12 months

Exclusion criteria

All couples with a reason of potential sub- and infertility, or not being

exposed to risk of conception or trying for pregnancy with the help of

Page 3 of 10

P.Frank-Herrmann et al.

fertility (Frank-Herrmann et al., 1991). Women who had either

delivered a child or breastfed or used oral contraceptives were only

included after 3 months of an established luteal phase, diagnosed by

an elevated temperature phase for at least 10 days. All the women

were asked to agree to participate for at least 12 cycles.

All the pregnancy charts were reviewed and conﬁrmed by the scienti-

ﬁc committee of the NFP study centre.

Deﬁnition of the unintended pregnancy

Pregnancies were classiﬁed as intended or unintended on the basis of

the statements made by the women before conception. At the end of

each menstrual cycle, the woman was asked to state if she was plan-

ning to become pregnant the following cycle. This was documented

in the completed cycle chart. If she forgot to answer this question,

and if a pregnancy occurred in the next cycle, it was always classiﬁed

as an unintended pregnancy. If charts did not reach the study centre in

time, the last indicated family planning intention held at the study

centre was used to classify a pregnancy as intended or unintended.

Teaching the STM

All the women who participated in the study were taught the STM by

accredited teachers from the ‘Arbeitsgruppe NFP’ which was founded

in 1981 with the aim of promoting NFP in Germany. In collaboration

with the German NFP study centre, the training and the teaching meth-

odology was standardized and adhered to strict guidelines. There were

comprehensive teaching materials that accompanied the personal

small group teaching sessions (Arbeitsgruppe NFP, 2006).

Data analyses

Statistical analyses were carried out using the SAS w package, version

8. We used the non-parametric model of Kaplan – Meier, the survival

curve or actuarial curve, to estimate the rates of unintended pregnancy,

the drop out due to dissatisfaction and the women lost to follow-up

(Kaplan and Meier, 1958; Matthews and Farewell, 1996). We

deﬁned the ‘survival’ of a woman as the duration in the study until

she dropped out for the target event (¼ unintended pregnancy).

Other dropouts are censored. The time unit was the menstrual cycle,

therefore, the estimated rates correspond to the life table approach

of Tietze and Potter, often used in earlier family planning studies

(Potter, 1966; Tietze and Lewit, 1974). In contrast to the Pearl-index,

the actuarial curves according to Kaplan – Meier represent a time-

related hazard estimation. The results at observation cycle 13 can

roughly be compared to the Pearl-index (¼ number of unintended

pregnancies per 100 women years, deﬁning 13 cycles to be one

woman year). To compare the actuarial curves of different parameters,

a logrank test was performed. Chi-squared-test was used for categori-

cal data.

The Kaplan – Meier approach was used to calculate the overall

effectiveness rates. Pregnancies due to both method and user failure

were included.

In order to calculate the method effectiveness, we used a modiﬁed

model of the ‘perfect/imperfect-use’ approach (discussed earlier,

Trussell and Grummer-Strawn, 1990): pregnancy rates were calcu-

lated according to sexual behaviour: all unintended pregnancies that

occurred during a deﬁned mode of sexual behaviour were related to

all cycles of the corresponding type of sexual behaviour,

i. e. unintended pregnancies that occurred in cycles with protected

intercourse during the fertile time were related to only those cycles

with protected intercourse in the fertile time. According to this

approach, we deﬁned the following categories of sexual behaviour

in the fertile time: only abstinence, only protected intercourse,

protected and unprotected intercourse, only unprotected intercourse,

coitus interruptus or genital contact.

Recruitment of study participants

The participants were volunteers who had self-selected to join the

study following given standardized information about the study by

their STM teachers; all women gave their informed consent. Standar-

dized admission questionnaires were used to collect relevant data con-

cerning age, parity, family planning history and socio-demographic

background. All women were asked to send their cycle charts, after

each cycle was completed, that recorded basal body temperature,

quality of cervical secretions, cycle length, family planning intention

and sexual behaviour directly to the study centre. Those women,

whose cycle charts did not reach the study centre, were contacted on

three separate occasions by the study centre via the woman’s personal

teacher. If a woman did not respond to any of the requests for infor-

mation she was then classiﬁed as lost to follow-up.

Discontinuation

We were speciﬁcally investigating the acceptability of the STM.

Therefore, the most important reasons given for discontinuation

were those due to dissatisfaction with the STM, and/or change to

other family planning method.

Table III lists all the reasons for discontinuation.

Data collection

The software used to handle the data was a Microsoft Access w rela-

tional database system called NFP DAT 1.0; it is described in a pre-

vious paper (Gnoth et al., 1999). It has an automated analysis

system that follows-up the participant every 3 months.

Deﬁnition of the pregnancy

The deﬁnition of pregnancy was an elevated temperature of longer

than 18 days and clinical pregnancy test conﬁrmed by the researcher.

Table III. Reasons for discontinuation during the effectiveness study

Results

To evaluate the overall use-effectiveness as well as the

method-related discontinuation and lost to follow-up, we

studied the following groups:

(i) Out of the whole cohort of 900 women and 17 638

cycles, we calculated the overall use-effectiveness as

well as the method-related discontinuation, the lost to

follow-up and the overall duration of study

participation.

(ii) This whole cohort was divided into two subgroups: 322

women used only the STM (‘STM only’-group) and

Reasons for discontinuation

Desire to get pregnant

Unintended pregnancy

Discontinuation because the couple was dissatisﬁed with the method:

discomfort with the method, problems with observing the indicators of

fertility, feeling of insecurity, ﬁnding the fertile time too long, ﬁnding it

difﬁcult to abstain during this time

Change to other family planning method

The woman does not want to be part of the study any longer; however, she

will continue practising the symptothesmal (STM) method

Medical or surgical reasons (e.g. Hysterectomy)

Separation from partner

Page 4 of 10

Effectiveness of a fertility awareness-based method

509 women used the STM with occasional use of bar-

riers in the fertile time (‘STM mix’-group). The ‘STM

mix’-group used a barrier method in 53% of their

cycles. Life table pregnancy rates have been analysed

separately for these two groups. Sixty-nine women

did not document their sexual behaviour and were

therefore excluded from that analysis.

To analyse the pregnancies according to the modiﬁed ‘perfect/

imperfect-use’ model, we formed different categories as

described earlier.

a univariate point of view, we calculated slightly different

rates of 1.62 (1/2 0.89) for the STM only-group versus

2.02 (1/2 0.72) for the ‘STM mix’ group at 13 cycles –

which corresponds approximately to 1 year. At 24 cycles the

differences were inversed. These differences were not found

to be statistically signiﬁcant at any time (Logrank test:

x 2 , 0.31, hence P . 0.60).

Figure 2 illustrates the overlapping standard errors.

Pregnancy rates in relation to sexual behaviour

in the fertile time

In order to accurately estimate the true method effectiveness

according to the ‘perfect/imperfect-use’ approach, every type

of sexual behaviour had to be documented. Charting of

sexual behaviour occurred in 85% of the cycles; analyses of

these cycles showed that in more than a third the STM was

used with abstinence during the fertile time, which reﬂects

the ‘perfect-use’ scenario and true method effectiveness. For

perfect use, the unintended pregnancy rate was 0.43 per 100

women and 13 cycles (Table VII).

In contrast, the rate of unintended pregnancies in cycles with

unprotected intercourse during the fertile time the unintended

pregnancy rate was signiﬁcantly higher with 7.47 per 13

cycles (P , 0.00001) and 100 women (Table VII and

Figure 3). In 16 of the 22 pregnancy cycles, there was unpro-

tected intercourse in the fertile time.

Client proﬁle

The socio-demographic characteristics of the study population

are shown in Table IV More than 60% of the women were

between 19 and 29 years old. Nearly two-thirds of the

women had a medium educational level (German baccalaureate

or equivalent without a university degree), 52% were nulligra-

vidas; about 20% had reached their desired family size and

nearly 60% of the women wanted a further child in the future

but not during the year of the study.

Overall unintended pregnancy rates (use-effectiveness)

For the whole cohort, we calculated an unintended pregnancy

rate of 1.79 ( þ /2 0.52 standard error) per 100 women after

13 months of use (Table V); all unintended pregnancies due

to method and user failure were included. There was no differ-

ence between the learning phase (ﬁrst 3 months of use) and the

subsequent months of use.

We compared the rates of unintended pregnancies between

the two groups ‘STM only’ and ‘STM mix’ (Table VI). From

Discontinuation

Discontinuation for dissatisfaction or difﬁculties with the

method, including change to another family planning method

was an important parameter of acceptability. The overall dis-

continuation rate for this category was 9.2 per 100 women at

13 cycles of method-use (Table VIII).

The overall rate of lost to follow up was 6.7% after 13 cycles

(Table VIII).

Other reasons for discontinuation before cycle 13 given by

34% of the couples included: desire to achieve a pregnancy

(8%); separation from partner (2%); medical reasons (4%)

and most frequently (22%) because they wished to discontinue

participating in the study, although they wished to continue to

use the STM.

Table IV. Socio-demographic characteristics of the cohort at study entry

(n ¼ 900)

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