For this week’s Featured Research we have a double review of “A Prospective Multicentre Trial of the Ovulation Method of Natural Family Planning II The Effectiveness Phase” and “Further Analysis of Contraceptive Failure of the Ovulation Method”.  As always, click through to the articles for a complete description of the original studies.

by Molly Marie Daley

A Five-Country Ovulation Method Study

How effective is your family planning method? If you use the Ovulation Method to avoid pregnancy, you are in luck. The World Health Organization (WHO) organized a task force to conduct the first international study of the ovulation method.[1] Two groups analyzed the data collected from this study; although these groups used different approaches when analyzing the data, both concluded that the ovulation method is an effective way to space or limit pregnancies.

The study included women from five countries: New Zealand (Auckland), India (Bangalore), Ireland (Dublin), Philippines (Manila), and El Salvador (San Miguel).[2] Seven hundred twenty-five women from these five countries successfully completed the study through the effectiveness phase.[3] During the study, these women learned and used the Ovulation Method, a natural family planning method “based on self-observation by the woman of a sequence of changes in the quality of cervical mucus.”[4] The women recorded their mucus or fluid symptoms and participated in monthly interviews with their teachers about their cycles, comprehension of and attitude towards the method, and their intentions regarding future pregnancies.[5] Almost all of the women participating were able to correctly identify the fertile period based on their self-observation, and only 2.2% of women discontinued the method because of dissatisfaction.[6]

User-Error/Method-Error Analysis: Finds OM Effective

The WHO task force analyzed the Ovulation Method’s effectiveness by calculating method and user failure. The method failure rate (the rate of pregnancies that resulted despite the couple observing all of the Ovulation Method rules) was 2.8. The user error rate (the rate of pregnancies that resulted when, for different reasons, the couple did not observe all of the Ovulation Method rules) was 19.5.[7] It’s important to note that user error includes, not only the pregnancies that resulted from inadequate teaching or inaccurate application of the Ovulation Method rules, but also the pregnancies that resulted from couples’ conscious decisions to break those rules to achieve pregnancy. There is a big difference between getting pregnant because you intentionally broke the Ovulation Method rules and getting pregnant despite trying to follow the Ovulation Method rules. Significantly, the user failure rate when couples chose to depart from the Ovulation Method rules was 15.4, while the user failure rate when couples intended to follow the rules was only 4.4. Essentially, the method was more than 95% effective even when couple were using it to avoid pregnancy

This task force concluded, not only that advocates of natural family planning methods will be encouraged by their findings, but also that even skeptics may be interested to learn more about the relative success of the method in the developing country centers.[8]

Perfect/Imperfect Use Analysis: Finds Ovulation Method Effective

The second group that analyzed the WHO data believes it is more accurate to analyze effectiveness rates by calculating perfect use and imperfect use. Because this second analysis was a patient recall/retroactive study, it is of lower quality and as such, it is classified as a “Sort Level 2.” This group concluded that the Ovulation Method is impressively effective when used perfectly, and very ineffective when used imperfectly.[9]


You might be wondering what constitutes “imperfect use.” The authors calculated imperfect use only for those cycles in which a couple disregarded one or more of the Ovulation Method rules. Why are these Ovulation Method rules important? The Ovulation Method rules are the family planning method itself. The Ovulation Method does not use any devices, pills, substances, inserts, or barriers; it is simply a list of instructions that the couple must follow when trying to avoid pregnancy. Therefore, calculating imperfect use based only on the cycles when couples did not follow the rules is akin to calculating the effectiveness rates for an artificial method when the couple did not use the method. (Instructions differ when the couple is trying to achieve pregnancy.) The list of Ovulation Method rules is basically a list of the times when a couple who wants to prevent pregnancy should avoid intercourse because the woman’s biomarkers have indicated that she is in a fertile phase of her cycle. When a couple has intercourse during this fertile phase, they are very likely to get pregnant. For example, if they have intercourse within 3 days after the peak, on the peak day, or around a second peak, there is a 95% chance that the woman will become pregnant within one year.[10]

Interestingly, the researchers themselves did not “follow the rules” when calculating the effectiveness rates. Specifically, in Ovulation Method a couple is instructed not to have sex in the initial cycle, so a woman can learn to make accurate observations of her cervical fluid without interference from semen. However, the researchers excluded cycle one from their analysis because women would not have “exposure” to potential pregnancy.  This shows that the researchers themselves completely ignore this rule that is used in teaching the method.

Final thoughts

One of the strengths of the Ovulation Method (like that of all fertility awareness-based methods of family planning) is the ease with which couples can switch their intentions from avoiding pregnancy to achieving pregnancy, or vice versa. (This is why it is not accurate to simply categorize FABMs as birth control.) If a couple says they are trying to avoid pregnancy but knowingly has intercourse on a day when they know the woman is fertile, they are saying one thing while doing the opposite. If you don’t follow the rules, you aren’t using the method. As the old adage goes, actions speak louder than words!

Molly Marie Daley received her bachelors degree in Religious Studies and Arabic from The College of William and Mary, and holds a Juris Doctor from The University of Maryland School of Law. Molly works as an advocate for fertility awareness and she now lives in the San Francisco Bay Area with her husband Nick.  She can be reached at, on Facebook (Molly Daley), or on Twitter (@mollymdaley).


A prospective multicentre trial of the ovulation method of natural family planning. II. The effectiveness phase. Fertil Steril. 1981 Nov;36(5):591-8.

Trussel and Grummer-Strawn. Further analysis of contraceptive failure of the ovulation method. Am J Obstet Gynecol. 1991 Dec;165(6 Pt 2):2054-9.

[1] Effectiveness Phase, 597; “No previous study of the OM has attempted a cross-cultural assessment of the effectiveness of the OM, although a number of prospective studies have done so in individual countries.” (See Effectiveness Phase footnotes 5-9)

[2] Further Analysis, 2055; of the 869 women entered the teaching phase, 83% were Catholic, 44%-66% had at least 6 to 12 years of schooling, 60% had been in their present union for more than 5 years, nearly all were housewives, and 36% had never used any type of family planning method (Effectiveness Phase, 593).

[3] Effectiveness Phase, 592

[4] Effectiveness Phase, 591

[5] Effectiveness Phase, 592; interestingly, 6.8% of women who had stated that they desired more children became pregnant, compared with only 3.8% of women who had stated they did not. (Effectiveness Phase 593)

[6] Effectiveness Phase, 595-597

[7] Effectiveness Phase, 591

[8] Effectiveness, 597

[9] Further Analysis, 2059

[10] Further Analysis, 2057

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