Typical Use Effectiveness of the Creighton Model: A Review of Research
By: Daniel Smith, DO
Director’s Note: Last week, we shared an excellent overview of the medical and surgical applications of the Creighton Model via NaProTechnology. This week, we continue our discussion of the Creighton Model with research  summarized by Dr. Daniel Smith. The study followed more than 700 couples learning the Creighton Model to explore typical use effectiveness rates, the teaching process, and patient adherence to the method.
Fertility awareness-based methods (FABMs) or natural family planning (NFP) is a growing field in modern medicine as more women and couples seek alternatives to avoid and achieve pregnancy. While there are other methods to avoid pregnancy, such as hormonal and barrier methods, these may not always be good options depending on a woman or couple’s preferences, beliefs, and health. In the early days of NFP, much of the data on method effectiveness to avoid pregnancy was controversial due a lack of standardization. The Creighton Model Fertility Care System (CrM) was developed as a cervical mucus-only method similar to the Billings Ovulation Method. However, the Creighton Model incorporates a standard process to monitor and record cervical fluid observations and to train professionals to properly teach patients how to use the system.
With the Creighton Model, a standardized method entered the field of natural family planning. The study by Howard et al  summarized below is titled, “Pregnancy Probabilities During Use of the Creighton Model Fertility Care System.” Published in 1999, the research focused on the pregnancy probabilities with typical use of the CrM. With the science of NaProTechnology now available, the method evolved beyond effective family planning to provide ways for women to monitor their health, while physicians apply its principles to diagnose and treat common women’s health conditions.
“With the science of NaProTechnology now available, the method evolved beyond effective family planning to provide ways for women to monitor their health, while physicians apply its principles to diagnose and treat common women’s health conditions.”
This study was conducted at St. Joseph Hospital in Houston, Texas from 1983 to 1989. It consisted of 701 primarily affluent couples that were mostly white (83%), college educated (58%), and between the ages of 20 and 34 (88%). Approximately 75% of participants were of Roman Catholic faith. Participants were enrolled in the study as they began to chart their cycles.
All women were given introductory teaching of CrM and were asked to track their cycles by charting menstruation and vaginal discharge. All participants were instructed to wipe across the vulva each time they used the bathroom to look for vaginal discharge and, if present, to chart its stretch, color, and lubricative feel. After the initial teaching and cycle tracking, participants attended multiple follow-up visits with an NFP professional who evaluated their charts and verified understanding of the CrM method and teachings.
If pregnancy occurred, a thorough evaluation was done during the first 3 months of pregnancy to assess the intentions and circumstances surrounding the pregnancy (proper documentation, intent to achieve pregnancy, failure of proper CrM use, failure of proper CrM teaching, or unrelated).
The 701 couples enrolled in this study were followed for 18 months. At 12 months, the net pregnancy probability was 17.12 per 100 couples, and 21.26 at 18 months. The probability of leaving the study for non-pregnancy reasons was 27.39 out of 100 couples at 12 months and 34.09 at 18 months. Therefore, the total probability of leaving the study for any reason was 44.51 at 12 months and 55.35 at 18 months. Leaving the study was primarily due to loss to follow up (17.40 at 18 months); other causes included moving from the area (7.28 at 18 months), switching to non-NFP contraception (5.14 at 18 months) or switching to another method of NFP (0.71 at 18 months).
Most pregnancies in the study (12.84 at 12 months; 16.83 at 18 months) resulted from couples engaging in achieving-pregnancy-related behavior (intercourse or genital contact during a time known or suspected to be fertile). In less than 3 per 100 couples, pregnancy resulted from user error, teacher error or a combination of both. The intentions behind a few of the pregnancies were unresolved due to a lack of data. There was only 1 method-related pregnancy recorded in the study.
“In less than 3 per 100 couples, pregnancy resulted from user error, teacher error or a combination of both.”
When compiling the data, the following subgroups were organized based on reproductive characteristics at the start of the study: uncomplicated regular cycles, long cycles, recent discontinuation of OCPs, currently/weaning breastfeeding, and others (combination of 40+ years old, postpartum but not breastfeeding, and 1 cycle after abortion). The data was fairly consistent, with the lowest overall probability of pregnancy per 100 couples in the uncomplicated regular cycles category (13.98) and the highest in the breastfeeding category (23.81). All other categories were similar, ranging from 17.65 to 18.40. Total probability per 100 couples was 17.12 at 12 months. This is important because it indicates similar effectiveness of the method across different reproductive situations.
This study followed use of the CrM in the real world. Beyond assessing the method for pregnancy prevention, the unique study design enabled the researchers to assess behaviors leading to pregnancy. For example, couples who engaged in intercourse on known days of high fertility were classified as engaging in “achieving-pregnancy-related behavior” whether or not they were “planning a pregnancy.” Aware of the high probability of pregnancy on highly fertile days (or sometimes days of unknown fertility because of incomplete tracking), these couples risked pregnancy by choosing to engage in intercourse that particular day.
This design is largely a departure from other studies which seek to document the efficacy of contraception methods to prevent pregnancy, as it makes room for such “informed departure of the rules” in real life to be included in the study. This is both a pro and a con: it allows for a more generalized observation of the method as it applies to the general public but also adds complexity when trying to define its true effectiveness or trying to compare to other methods. Some, but not all “achieving-related pregnancies” would also be “planned pregnancies” if intentions had been assessed in a traditional manner. Since these “achieving-pregnancy-related behavior” pregnancies are not excluded from the data as “planned pregnancies,” the total pregnancy rate per 100 couples in this study is artificially high when compared to “unplanned pregnancy rate” of other studies of other contraceptive methods (many of those studies would have excluded planned pregnancies from the pregnancy rates). Thus, comparing this data to that of most studies assessing the efficacy of contraceptive methods is difficult. Furthermore, this article was published in 1999 and the study was completed in the ‘80s with a non-diverse group of subjects, making it difficult to apply to a modern general public.
“Since these “achieving-pregnancy-related behavior” pregnancies are not excluded from the data as “planned pregnancies,” the total pregnancy rate per 100 couples in this study is artificially high when compared to “unplanned pregnancy rate” of other studies of other contraceptive methods.”
When identifying the causes of pregnancy, this study classifies pregnancies resulting from forgetfulness or misunderstanding as separate from method-related pregnancies. Yet, in counseling couples about pregnancy rates, it is important to keep the pregnancies due to user/teacher error in mind in addition to solely method-related pregnancies. Many NFP methods can be complex, require frequent log keeping, and have some level of subjectivity. For example, seminal fluid or lubricants can interfere with the evaluation of cervical mucus. When choosing the best method for them, it is important for couples to learn how to avoid these mistakes.
Despite its limitations, this study established the Creighton Model as a viable method of family planning, provided a basis for further research, and contributed to the development of future NFP methods.
 Howard MP. Pregnancy probabilities during use of the Creighton Model Fertility Care System. Archives of Family Medicine. 1999;8(5):391-402. doi:10.1001/archfami.8.5.391.
ABOUT THE AUTHOR
Daniel Smith, DO
Daniel Smith, DO is a PGY-1 internal medicine resident at Harris Methodist Hospital in Fort Worth, TX. He completed his medical education at Des Moines University in Des Moines, IA and undergraduate education at Texas A&M University in College Station, TX. Dr. Smith enrolled in the FACTS elective to gain a better understanding of natural family planning methods, as he did not believe he would have the opportunity after starting residency.