Introduction

Background

Sexual intercourse has to take place within the fertile window of the woman’s cycle to make the most of a particular couple’s natural conception potential. For most women, even those with relatively regular menstrual cycles, the time of ovulation and the fertile window vary markedly. More than half of the women in a normal population have a variation in cycle length and fertile window of at least 1 week observed over 1 year [1–4]. This is no problem if couples have intercourse every 1–2 days throughout the whole cycle, as recommended by the ASRM in 2008 [5]. However, this frequency is not reached in reality especially over longer periods of time [6, 7]. This means that couples may be inaccurate in timing sexual intercourse to occur during the woman’s fertile time. Many couples trying for pregnancy believe that they are most fertile around day 14 and target frequent intercourse between days 10 to 16; they are then likely to have a reduced frequency of sexual intercourse from day 17 onwards [1]. But in a 33-day cycle, peak fertility may occur at around day 20. Therefore, inaccurate timing of sexual intercourse may be a reason for delay in conception or ongoing subfertility, indicating the need for accurate fertility awareness education.

The natural family planning (NFP) method called Sensiplan is a fertility awareness method (FAM) that enables a woman to accurately identify her fertile time [8]. Women observe and interpret cycle symptoms, mainly cervical secretion changes and basal body temperature, which have been proven to be reliable indicators of the fertile window [1, 9–13]. The Sensiplan method’s guidelines are evidence based and have been developed following extensive fertility research carried out over the last 25 years [13]. They have been adopted and disseminated by several European NFP groups [1, 8, 14]. This paper describes a study cohort of subfertile couples who were trained to identify the fertile phase of the menstrual cycle using the Sensiplan method.

Correlation studies have shown that estimates of peak fertility and ovulation based on cervical secretions and basal body temperature rise have a high probability of being within 1–2 days of true ovulation (detected by ultrasound and LH peak) [2, 9, 10, 15, 16]. Several probability-of-conception studies have identified the fertile phase as beginning 5 days prior to ovulation, and extending to the day of ovulation [17–20]. Furthermore, these studies found that timing intercourse to occur on days with good cervical secretion quality was more important for achieving pregnancy than planning sexual intercourse to coincide with the time of likely ovulation [17, 21].

There is some evidence that fertility awareness education shortens the time-to-pregnancy (TTP): a prospective cohort TTP study followed up 340 healthy German women using the Sensiplan method from their first cycle trying for pregnancy. The pregnancy rates at 1, 3, 6 and 12 cycles were 38, 68, 81 and 92%, respectively [22]. In their guidelines on “Optimizing natural fertility” the American Society for Reproductive Medicine (ASRM) cites this German study in relation to the good results on the spontaneous achievement of pregnancy following unprotected intercourse [5, 23]. However, it was not explicitly mentioned that those rates were achieved by women who had been trained in fertility awareness methods, i.e., who knew how to identify their fertile window precisely.

Around 9% of couples fail to conceive within 12 months of trying [24, 25]. Increasingly these couples are being referred to assisted reproductive technology (ART) clinics for subfertility treatment. There is a paucity of data related to pregnancy rates in subfertile women who use fertility awareness methods (FAM) [26–28].

Objectives

The primary aim of this study was to determine the cumulative spontaneous conception rate after subfertile couples were trained to identify their fertile window.

A secondary aim of the study was to explore whether the planning and implementation of diagnostic tests for subfertility can be performed more efficiently if the fertile window is identified; the results of this investigation will be presented in another paper.

Materials and methods

The study was conducted between 2004 and 2008 by the Department of Gynecological Endocrinology and Fertility Disorders of the Women’s Hospital of the University of Heidelberg/Germany. The purpose of this exploratory study with high external validity was to estimate the efficiency of the Sensiplan method of fertility awareness in aiding subfertile couples to achieve natural conception.

Inclusion criteria

Participating couples in this prospective cohort study were selected according to the following criteria:

  • at least 1 year of unsuccessfully trying to conceive

  • absence of amenorrhea

  • currently receiving no subfertility treatments

  • willing to learn and use the Sensiplan method of fertility awareness

  • willing to participate for at least two cycles and to complete and deliver two FAM charts

  • willing to fill out three questionnaires over the course of the study. The questionnaires were designed to collect information on prior medical history relating to subfertility as well as user satisfaction and competence in use of the FAM method.

  • no known tubal occlusion

  • no known severe OAT (oligoasthenoteratozoospermia, OAT III).

Study design

During the first study consultation, information was collected about each woman’s previous and current medical and reproductive history, and on their fertility awareness knowledge. The charting and use of the Sensiplan method was also explained. The observation period started with the following menstrual period. After the first cycle, a follow-up consultation was carried out by telephone to enable the women to discuss their first cycle chart. The women were asked to return for diagnostic tests during a subsequent cycle. Basic subfertility investigations were carried out during that cycle, including a day 2–5 basic hormonal profile (blood test). When the patient observed clear, stretchy, and slippery cervical secretions for the first time in that cycle, she underwent a transvaginal ultrasound investigation the following day and blood test was taken to monitor periovulatory hormonal levels. A third blood test was taken 1 week later to monitor the hormonal levels of the luteal phase. 83% of male partners had a basic semen analysis.

All couples were requested to stay in the study until they achieved pregnancy or for up to 8 months. The first chart and the chart of the diagnostic cycle were collected. Some participants had already scheduled ART treatments when they became part of the study, and were observed for a smaller number of cycles before moving on to ART. All study pregnancies were confirmed by temperature charts and by ultrasound.

The fertility awareness method

The Sensiplan method consists of recording the pattern of cervical secretion and changes in basal body temperature. Women are trained to observe the presence and type of cervical secretions from the vulva over the course of the day and record sensation and appearance of the secretions prior to going to bed at night. Basal body temperatures were measured in the morning after waking up. Self-observation of the cervical secretions serves as a predictive marker for ovulation and is confirmed by a temperature rise, which indicates the closing of the fertility window. The beginning and the end of the fertile time are determined in the following way, and can be considered ‘rules’ for couples trying to conceive (The guidelines for achieving pregnancy differ from those for avoiding a pregnancy):

  • The beginning of the fertile time is identified by the first appearance or sensation of cervical secretions on the vulva and lasts until the third day after the peak day of secretions.

  • The end of the fertile time is additionally confirmed by the rise in basal body temperature related to the progesterone surge. The temperature rise is recognized by three higher readings, all three higher than the previous six readings and the last one 0.2 °C higher than the previous six. The elevated temperature retrospectively indicates ovulation has occurred; the temperature remains elevated until the next menstruation [29, 30].

The methodology is described in detail elsewhere [29].

The behavioral advice given to couples who wish to conceive is that conception is likely to be highest on those days when clear, stretchy, and slippery secretions are present, as well as on the two consecutive days following this time. Sexual intercourse should be targeted on days when cervical secretions are present and for 2 days after the peak secretion day, up to the first higher temperature reading, even if secretions are no longer present. Couples are told that they may have intercourse as frequently as they like. It is recommended that intercourse should occur at least every 2 or 3 days during the fertile window.

Statistical analysis

Statistical analyses were performed with SPSS 22 and BiAS for Windows 10. Because the study length of eight cycles precluded calculation of the median cycle rate for becoming pregnant, we report the mean cycle rate. The main results are purely descriptive, with absolute and relative frequencies, Kaplan–Meier curves and stratified life tables. The Hall–Wellner method was used to produce a 95% confidence interval. It should be noted that we use the odds ratio instead of the appropriate term, “relative hazard”, for pregnancy incidence.

As inference statistics we applied Cox regression with difference as contrast for stratified age and time-to-pregnancies. Further, we used Cox regression to adjust for real age in years in the description of women who became pregnant despite secondary subfertility diagnoses such as endometriosis. We stratified our results for duration of childlessness and age of the woman according to the relevance of subfertility co-factors [31].

Due to the study’s exploratory nature, we did not adjust for multiple testing of each subject.

Study population

In total, 194 patients were recruited into the study. One-third of the cohort was recruited via the Subfertility Clinic at the Women’s Hospital of the University of Heidelberg; the other couples were recruited via advertisements in the local newspaper. Seven women (3%) became pregnant during the last cycle before starting Sensiplan and were hence excluded from the study, so that the study population consisted of 187 women who had been trying for pregnancy for at least 1 year before study entry. We did not exclude cases with diminished male fertility (except OAT III if known).

51% of the participants were 35 years or younger (Table 1). Their ages ranged from 21 to 41 years, with a mean of 34.7 (SD = 4.9 years) and a median of 35.

Table 1 Age, education and years seeking to become pregnant (n = 187 women)
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48% of the participants had been trying to conceive for at least 3 years (mean of 3.5 years).

81% of the women had never been pregnant prior to the study. 11% had already given birth to one or more children with the same partner, 4% with another partner, and 9% had undergone one or more abortions.

96% had received no prior instruction on monitoring cervical secretions.

Based on the results of the tests of the diagnostic cycle, the couples were classified according to their subfertility diagnosis (Table 2).

Table 2 Reasons for subfertility (n = 187 women, multiple reasons possible)
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Results

69% (n = 129) of the study participants completed the study, i.e., they either completed 8 months or became pregnant. 31% of the couples discontinued from the study prior to completing eight cycles, primarily due to their commencing subfertility treatments (fertility awareness training was offered to them while they were on the ART waiting list). Only 2% of the women withdrew due to problems related to learning about self-observation of cervical secretions and/or monitoring their basal body temperature. Another 3% of the women discontinued the study because it was identified that pregnancy was no longer possible and a further 3% decided they no longer wished to achieve a pregnancy. The low lost-to-follow-up rate of 1% indicates good study implementation (Table 3).

Table 3 Reasons for study drop-out (n = 187 women)
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Spontaneous pregnancy rate with fertility-focused intercourse

The cumulative spontaneous pregnancy rate with fertility focused intercourse was 38% (95% CI 27–49%) after 8 months of observation (Kaplan–Meier curve with 58 pregnancies) which is above the estimated spontaneous pregnancy rate without fertility awareness training (Fig. 1). The mean time-to-pregnancy was 6.4 cycles.

Fig. 1
figure 1

Cumulative natural conception rate after Sensiplan training (n = 187 subfertile women)

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The 3% spontaneous pregnancy rate during the cycle directly preceding the training cycle may be considered the spontaneous pregnancy rate for one cycle without fertility awareness training. This gives the basic, intrinsic, cumulative pregnancy rate of up to 21.6% during the eight cycles of study duration (p = 1 − (1 − 0.03)8, conservatively calculated; power to basis 0.97 or 0.978 cycle) for statistical comparisons.

Spontaneous pregnancy rate depending on age

The spontaneous pregnancy rate depending on age is presented in Table 4 and Fig. 2. The women were stratified into three age groups (below 36, 36–40 years and above 40 years). Women 35 years or younger achieved significantly more spontaneous pregnancies than women aged 36 and above (log-rank test, p = 0.018). For those under 36 years, the probability of spontaneous conception after 8 cycles was 51%; for 36–40 year-olds it was 25% and 20% for those over 40 years.

Table 4 Cumulative probability of natural conception in different age groups after Sensiplan training (n = 187 subfertile women)
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Fig. 2
figure 2

Cumulative natural conception rate in different age groups after Sensiplan training (n = 187 subfertile women)

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If age is considered as metric variable in a Cox regression model, the chance of becoming pregnant was reduced by about 8% with each passing year [p = 0.001; Odds ratio 0.92 (95% CI 0.87–0.97)].

Spontaneous pregnancy rate depending on the duration of subfertility

The participants were also stratified into three groups according to the length of time spent attempting to achieve pregnancy prior to the study (1–2 years, 3–4 years, more than 4 years). For those couples trying to become pregnant over the previous 1 to 2 years, the pregnancy rate increased to 56% 8 months after Sensiplan training (significantly different to the basic pregnancy rate, p < 0.001 in the log-rank test) (Table 5; Fig. 3). Amongst the couples who had tried to achieve pregnancy for between 3 and 4 years, there was a spontaneous pregnancy rate of 20% after 8 months (Kaplan–Meier). Amongst those couples with more than 5 years of subfertility, three pregnancies occurred spontaneously (11%), all shortly after receiving fertility awareness teaching.

Table 5 Cumulative probability of natural conception after Sensiplan training by duration of subfertility (n = 187 women)
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Fig. 3
figure 3

Cumulative natural conception rate after Sensiplan training by duration of subfertility (n = 187 subfertile women)

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The basic, intrinsic pregnancy rate of up to 21.6% without fertility awareness training is estimated from the seven women who became pregnant during the last cycle before starting Sensiplan, 6 of them attempting to achieve pregnancy since 1–2 years and 1 since 3 years.

There is a significant relationship between these two ordinal variables (Kendall’s tau 0.22, p = 0.001). If age and length of time seeking pregnancy are each stratified into three groups and considered together as categorical variables in a Cox regression model (with difference as contrast), seeking pregnancy for more than 2 years seems to be the most important factor [p = 0.006; Odds ratio = 0.38 (95% CIs 0.19–0.97)]. Despite the limitations of our study sample, we observed that seeking pregnancy for more than four years [p = 0.095; Odds ratio = 0.36 (95% CI 0.11–1.19)] and age greater than 35 years [p = 0.069; Odds ratio = 0.57 (95% CI 0.32–1.04)] seemed to reduce the chance of becoming pregnant by half. We saw no reason to stratify below and above 40 years of age (p = 0.672), and hence we present the pregnancy rates of two age groups, up to 35 years of age and above 35 years of age (see Table 4).

Spontaneous pregnancy rate in secondary infertility

No significant difference was found between the pregnancy rates of women with primary vs. secondary infertility: 32.8% (42 of 128) for women who had not previously been pregnant and 31.0% (18 of 58) for women who had already given birth or who had undergone an abortion.

Spontaneous pregnancy rates by diagnostic subgroups

Endometriosis, and diminished male fertility, all significantly reduce the chances of conceiving naturally (Table 6).

Table 6 Natural conception rates after Sensiplan training by diagnostic subgroups adjusted for age (n = 187 women)
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Subjective assessment of the influence of the fertility awareness method on the well-being of the women

A questionnaire on the assessment of the influence of the Sensiplan method on the well-being of the participant was completed at the end of study participation (n = 171, multiple answers possible). 78% of the participants reported that the training in identifying their fertility window positively affected their feelings towards and perceptions of their bodies. 53% reported that this knowledge had had a positive impact on their self-image as a woman. 11% of the women stated that their partnership had been negatively impacted through the observations of the fertile time. 16% of the women reported a negative effect on sexuality. Only 7% of women described the FAM method as bothersome or reported that they did not like to plan intercourse according to their fertile time. At the end of the study, 82% of patients stated that they planned to continue using the Sensiplan method or that they would use the method again if they were planning another pregnancy.

Discussion

38% of subfertile couples (who had been trying for pregnancy since an average of 3.5 years) were successful in achieving a pregnancy after receiving training in the Sensiplan method. In those couples who had been trying to achieve a pregnancy for between 1 and 2 years, the pregnancy rate increased to 56% after 8 months following FAM training. Duration of non-conception for more than 2 years, maternal age above 35, endometriosis and male subfertility significantly reduced the chances of conceiving naturally.

Does fertility awareness knowledge increase the spontaneous pregnancy rate in subfertile couples: more than just expectant management?

This observational cohort study lacks a control group. The intrinsic, basic, natural conception potential without fertility awareness training can be estimated, however. We consider the rate of 3% spontaneous pregnancies (n = 7) in the cycle directly preceding study entry to be the spontaneous pregnancy rate per cycle without fertility awareness training, yielding a cumulative estimated pregnancy rate of up to 21.6% (maximum) after 8 months.

An observational study by Snick et al. on spontaneous pregnancy rates in 726 couples attempting pregnancy for 1 year showed a live birth rate of around 25% after another 12 months and 52.45% after 36 months [32], confirming computational prognostic models [33]. Our comparatively higher pregnancy rates amongst couples using Sensiplan suggest that couples benefit from training in how to identify the fertile time through self-observation.

There are three randomized controlled studies on the effect of timed intercourse in the fertile window on pregnancy rates. Robinson et al. observed 305 subfertile women with and 348 without use of a fertility monitor, which measures urine E1G and LH levels [34]. After two cycles the pregnancy rate amongst women able to identify their fertile time was significantly higher (23 vs. 14%) than amongst the controls. The second randomly controlled trial is the Oxford conception study, which has not yet published final results [35]. In a randomized trial with 143 couples with proven fertility, Stanford et al. found no significant impact of the respective FAM vs. frequent intercourse [36]. Further randomized controlled trials studying the effect of fertility awareness training with self-observation methods are needed [37].

Moreover, several probability-of-conception studies have shown that the phase of peak fertility is rather narrow (2–3 days per cycle), and that conception probabilities quickly decline even within the fertile window [11, 20, 38, 39]. This physiological fact represents a further reason for targeted intercourse.

There is already considerable evidence suggesting that awareness of the fertile window is an effective method for enhancing the probability of conception in couples starting to try for pregnancy, and is likely to be more effective than expectant management [21, 22, 25, 40]. Evers analyzed a Cochrane database of hypothetical cumulative spontaneous pregnancy rates without controlled knowledge of the time of peak fertility, reporting that the time-to-pregnancy for 20% of women who were able to become pregnant was 1 month and for 74% of that group was 6 months [31]. In comparison, 42% of women who became pregnant while using the Sensiplan method were pregnant in 1 month and 75% were pregnant within 3 months, suggesting that women conceive more rapidly with fertility awareness knowledge [22].

However, further randomized trials on FAM in subfertile couples are needed: The Cochrane review undertaken by Grimes et al. in 2004 only addressed the contraceptive effectiveness of FAMs [41]. Furthermore, it was based on three old, low-quality studies.

Stress related to timing intercourse

As timed intercourse may cause stress, it is not recommended in several medical guidelines [5, 42]. These recommendations are based on one study only, a mail survey with 27 participants that has been criticized because of its poor quality [43]. Instead, the guidelines recommend intercourse every other day throughout the whole cycle. The impact of the stress caused by recommending continuous intercourse throughout the whole cycle has not been investigated to date either.

The argument for withholding knowledge about the fertile time for that reason is only theoretical, since most couples in the situation of seeking to become pregnant try to detect their fertile window in some fashion, but not all methods practiced provide useful and accurate information. An Australian study that followed 282 patients seeking subfertility care from ART clinics found that 87% actively tried to improve their fertility awareness knowledge using one or more information resources, and that most believed that they had targeted sexual intercourse during their fertile window. In fact, only 13% of the participants were able to correctly identify the fertile time [43, 44]. A further study involving 80 subfertile women seeking fertility care found that 76% could not accurately identify the fertile window [45]. These results suggest that poor fertility awareness knowledge may be one of the factors preventing couples from achieving their conception potential.

In addition, as any fertility investigation and treatment may cause stress, it is up to each couple to decide the suitable way to deal with their subfertility.

The accuracy of existing fertility awareness knowledge

While many women believe that they know when they are fertile, this has been shown to be inaccurate [43, 46, 47]. Sievert et al. interviewed 53 women who thought that they could identify their fertile window. Participants were asked to identify their fertile days over a period of 87 cycles [48]. Sievert et al. found that the women relied on the common knowledge on the fertile days which was obviously poor. They concluded that “for most women, ovulation is concealed” even if they think they know it. This supports our suggestion that women should be taught how to identify the fertile time correctly.

80% of women who were having trouble conceiving and who had attended a course led by a trained teacher of fertility awareness methods could identify the fertile time during their menstrual cycle [45]. The authors, therefore, propose that fertility awareness knowledge should be integrated into routine preconception consultations and into teaching of health professionals.

The observation of cervical secretions: an accurate predictor of the fertile time

A considerable amount of data suggests that observation of cervical mucus changes can closely approximate the day of ovulation, is easy to learn and suitable for a large cross-section of women [2, 9, 10, 15, 18, 49]. Scarpa et al. found in a time-to-pregnancy study with 193 women that the presence of cervical secretions accurately predicts the fertile time, and that the presence of cervical secretions on the day of intercourse is a better predictor of the likelihood of conception than targeted intercourse at likely time of ovulation [38].

The ASRM guidelines state that “the fertile time is a 6-day interval that ends on the day of ovulation and correlates with the volume and character of cervical secretions.” The guidelines additionally state that determining or predicting the time of ovulation may be useful for couples trying to conceive [5, 23].

Dunson et al. found that the presence of cervical secretions is an even better fertility marker than LH kits. Cervical secretions identify the whole fertile window more accurately, because they indicate more days when sexual intercourse may result in pregnancy. In their probability-of-conception analysis of a large European database of cycles, they identified that those couples with a single episode of sexual intercourse during the fertile time needed a larger number of cycles to achieve conception [50], see also [51, 52]. These findings indicate that the observation and monitoring of cervical secretions to identify the fertile time is a useful way to identify days when there is a high probability of conception if intercourse takes place.

The psychological impact of teaching fertility awareness to subfertile couples

Klann et al. noted a positive impact on self-awareness when the FAM is used to avoid pregnancy [7]. The present study is the first one that has investigated the psychological impact of the use of the Sensiplan fertility awareness method on a population of subfertile women based on a personal assessment. The results were that 78% of women assessed the effect of the method on their own body awareness as a positive one and 53% positively rated the influence on their self-image as a woman. While a minority of couples experienced a negative effect on their relationship (11%) and sexuality (16%) when taught fertility awareness methods, this is not the case for the majority of couples.

Providing fertility awareness as an integral part of the management of subfertility

As most pregnancies are likely to occur during the first few cycles of using the Sensiplan method, subfertile couples should be given a chance of achieving pregnancy for at least six cycles prior to any intervention. After receiving basic investigations for subfertility, couples could be encouraged to observe their fertile window to optimize their chances of achieving a pregnancy spontaneously, especially in those cases of unidentified or minor reasons for subfertility and for those women who are known to have sufficient ovarian reserve [53–55]. According to Evers, two important questions need to be addressed before any treatment for subfertility is offered [31]: Has sufficient exposure to the chance of conception taken place? Are cost-effective, safe, and reliable treatments available?

The authors believe that the integration of fertility awareness into subfertility care is likely to lead to significant cost savings in subfertility management. Further studies on the acceptability of learning fertility awareness in the condition of subfertility are recommended.

Conclusion

Training women to identify their fertile window in the menstrual cycle seems to be a reasonable, non-invasive and safe first-line therapy in the management of subfertility. Sensiplan is a standardized fertility awareness method that has the potential to improve spontaneous pregnancy rates in subfertile couples.