Evaluating Pregnancy Rates in Fertility Awareness-Based Methods for Family Planning: Simulated Comparison of Correct Use to Avoid, Method-Related, and Total Pregnancy Rates
Marguerite Duane , Rebecca G Simmons, Joseph B Stanford
Fertility awareness-based methods (FABMs), also known as natural family planning (NFP), enable couples to identify the days of the menstrual cycle when intercourse may result in pregnancy ("fertile days"), and to avoid intercourse on fertile days if they wish to avoid pregnancy. Thus, these methods are fully dependent on user behavior for effectiveness to avoid pregnancy. For couples and clinicians considering the use of an FABM, one important metric to consider is the highest expected effectiveness (lowest possible pregnancy rate) during the correct use of the method to avoid pregnancy. To assess this, most studies of FABMs have reported a method-related pregnancy rate (a cumulative proportion), which is calculated based on all cycles (or months) in the study. In contrast, the correct use to avoid pregnancy rate (also a cumulative proportion) has the denominator of cycles with the correct use of the FABM to avoid pregnancy. The relationship between these measures has not been evaluated quantitatively. We conducted a series of simulations demonstrating that the method-related pregnancy rate is artificially decreased in direct proportion to the proportion of cycles with intermediate use (any use other than correct use to avoid or targeted use to conceive), which also increases the total pregnancy rate. Thus, as the total pregnancy rate rises (related to intermediate use), the method-related pregnancy rate falls artificially while the correct use pregnancy rate remains constant. For practical application, we propose the core elements needed to assess correct use cycles in FABM studies.
Summary
Fertility awareness-based methods (FABMs) can be used by couples to avoid pregnancy, by avoiding intercourse on fertile days. Users want to know what the highest effectiveness (lowest pregnancy rate) would be if they use an FABM correctly and consistently to avoid pregnancy. In this simulation study, we compare two different
Measures
(1) the method-related pregnancy rate; and (2) the correct use pregnancy rate. We show that the method-related pregnancy rate is biased too low if some users in the study are not using the method consistently to avoid pregnancy, while the correct use pregnancy rate obtains an accurate estimate. SHORT
Summary
In FABM studies, the method-related pregnancy rate is biased too low, but the correct use pregnancy rate is unbiased.
fertility awareness-based methods pregnancy rates simulation, FABM correct use typical use pregnancy rate comparison, Stanford Duane Simmons FABM effectiveness simulation, natural family planning correct use effectiveness evaluation, simulated comparison fertility awareness pregnancy rates, Linacre Quarterly FABM effectiveness simulation 2024, billings symptothermal Creighton Marquette effectiveness, fertility awareness method unintended pregnancy rate, FABM typical use correct use rate methodology
PMID 39104463 39104463 DOI 10.1177/00243639231212440 10.1177/00243639231212440 Stanford et al. 2024, Stanford 2024
Cite this article
Stanford, J. B., Duane, M., & Simmons, R. (2024). Evaluating Pregnancy Rates in Fertility Awareness-Based Methods for Family Planning: Simulated Comparison of Correct Use to Avoid, Method-Related, and Total Pregnancy Rates. The Linacre Quarterly, 91(3), 315-328. https://doi.org/10.1177/00243639231212440
Stanford JB, Duane M, Simmons R. Evaluating Pregnancy Rates in Fertility Awareness-Based Methods for Family Planning: Simulated Comparison of Correct Use to Avoid, Method-Related, and Total Pregnancy Rates. Linacre Q. 2024;91(3):315-328. doi:10.1177/00243639231212440
Stanford, J. B., et al. "Evaluating Pregnancy Rates in Fertility Awareness-Based Methods for Family Planning: Simulated Comparison of Correct Use to Avoid, Method-Related, and Total Pregnancy Rates." The Linacre Quarterly, vol. 91, no. 3, 2024, pp. 315-328.
Stanford JB, 2004·The Medical and Surgical Practice of NaProTECHNOLOGY
Methodologically rigorous effectiveness data for the CrMS are presented, including method-effectiveness and use-effectiveness rates for pregnancy avoidance drawn from prospective cohort studies, demonstrating rates comparable to or exceeding hormonal contraception. Standardized outcome measurement is necessary to establish the CrMS's scientific credibility and to provide practitioners and patients with accurate, evidence-based counseling on system performance.
postpartum/return-of-fertility/postpartum-chartingfertility-awareness/effectiveness/typical-and-perfect-usecontraception/comparative-studies/contraception-versus-fertility-awareness
Open Access
The uses of cervical mucus and basal body temperature as indicators of return to fertility postpartum have resulted in high unintended pregnancy rates. In 2013, a study found that when women used urine hormone signs in a postpartum/breastfeeding protocol this resulted in fewer pregnancies. To improve the original protocol's effectiveness, three revisions were made: (1) women were to increase the number of days tested with the Clearblue Fertility Monitor, (2) an optional second luteinizing hormone test could be done in the evening, and (3) instructions were given to manage the beginning of the fertile window for the first six cycles postpartum. The purpose of this study was to determine the correct and typical use effectiveness rates to avoid pregnancy in women who used a revised postpartum/breastfeeding protocol. A cohort review of an established data set from 207 postpartum breastfeeding women who used the protocol to avoid pregnancy was completed using Kaplan-Meier survival analysis. Total pregnancy rates that included correct and incorrect use pregnancies were eighteen per one hundred women over twelve cycles of use. For the pregnancies that met a priori criteria, the correct use pregnancy rates were two per one hundred over twelve months and twelve cycles of use and typical use rates were four per one hundred women at twelve cycles of use. The protocol had fewer unplanned pregnancies than the original, however, the cost of the method increased.
fertility-awareness/effectiveness/typical-and-perfect-usecontraception/comparative-studies/contraception-versus-fertility-awareness
Open Access
Women of reproductive age need reliable and effective family planning methods to manage their fertility. Natural family planning (NFP) methods or fertility awareness-based methods (FABMs) have been increasingly used by women due to their health benefits. Nevertheless, effectiveness of these natural methods remains inconsistent, and these methods are difficult for healthcare providers to implement in their clinical practice. The purpose of this study is to evaluate the effectiveness of the Marquette Model NFP system to avoid pregnancy for women at multiple teaching sites using twelve months of retrospectively collected teaching data. Survival analysis (Kaplan-Meier) was used to determine typical unintended pregnancy rates for a total of 1,221 women. There were forty-two unintended pregnancies which provided a typical use unintended pregnancy rate of 6.7 per 100 women over twelve months of use. Eleven of the forty-two unintended pregnancies were associated with correct use of the method. The total unintended pregnancy rate over twelve months of use was 2.8 per 100 for women with regular cycles, 8.0 per 100 women for the postpartum and breastfeeding women, and 4.3 per 100 for women with irregular menstrual cycles. The Marquette Model system of NFP was effective when provided by health professionals who completed the Marquette Model NFP teacher training program.
This study involved determining whether healthcare professionals at ten sites across the United States and Canada trained to provide the Marquette Method NFP services can replicate the effectiveness demonstrated in previous studies of the method. We found a high level of effectiveness (i.e., very low pregnancy rates) in using the Marquette Method among women from various regions across North America with diverse reproductive backgrounds and in particular when using hormonal fertility marker. Healthcare providers who have been trained to teach NFP can successfully incorporate NFP services in their practice and assist their clients in choosing appropriate family planning methods.
fertility-awareness/effectiveness/typical-and-perfect-usecontraception/comparative-studies/contraception-versus-fertility-awareness
Open Access
Knowledge of the fertile and infertile phases of the menstrual cycle can be applied to conceive or to avoid pregnancy. Fertility intentions and sexual behaviors during the fertile time may influence whether and when pregnancy occurs. The Creighton Model FertilityCare System (CrMS) is a specific system of fertility appreciation used to conceive or to avoid pregnancy. The objective of this paper is to report intentions, behaviors, and pregnancy rates during use of the CrMS among couples who initially intended to avoid pregnancy.Data and methodsWe analyzed a prospective cohort study conducted in 17 CrMS centers across the USA and Canada, following 296 couples for up to one year after onset of initial use of the CrMS to avoid pregnancy. Baseline data included demographics, motivations, and pregnancy intentions for each partner. Couples contributed 2894 menstrual cycles, most of which had data collected (by questionnaires and daily diary) on cycle-specific pregnancy intentions, days of potential fertility, and fertility behaviors. Pregnancies were prospectively actively ascertained. We found a high concordance (91%) in cycle pregnancy intentions between partners. However, 44% of cycles with strong intentions to avoid pregnancy included intercourse on potentially fertile days or days of undetermined fertility status. Across all sensitivity scenarios, cumulative 13-cycle pregnancy rates with cycle intention to conceive ranged from 88.0% to 89.8%, and cumulative 13-cycle pregnancy rates with cycle intention to avoid ranged from 29.1% to 35.3%. In multivariate analysis, baseline motivations and intentions for pregnancy within 2 years were strongly correlated with the likelihood of pregnancy, more so than cycle intentions. The findings suggest that in some populations using natural family planning, baseline motivations and intentions may be more strongly related to pregnancy rates than cycle intentions. Our findings also highlight essential elements for evaluating correct use, including complete recording of intercourse and its timing.