Are FABMs effective, even during a Zika outbreak?

By: Alison Contreras, PhD and Marguerite Duane, MD, MHA

By now almost everyone has heard about Zika, the mosquito borne virus that is linked to microcephaly, a birth defect in which the baby develops a smaller than normal head. First discovered in Brazil, this virus has now been confirmed in the US.  Although the virus is typically spread through the bite of an infected mosquito, the first US case in Texas is thought to be through sexual contact. As governments recommend couples start delaying pregnancy for the next several months, this leaves many people wondering, just how effective is their birth control?

Are FABMs reliable for preventing pregnancy?

Although there are discrepancies in reported effectiveness rates for fertility awareness based methods (FABMs), the highest quality research studies available reveal that these methods are reliable.  Unfortunately, news sources are continuing to propagate inaccurate information about the effectiveness of FABMs claiming they are only 25% effective for preventing pregnancy, confusing myth with facts.

This misinformation makes it almost impossible for patients to make truly informed decisions.  As physicians and health care educators it is up to us to keep up to date with the best evidence available, so we can share this information with patients.

The following table highlights the highest quality studies for individual FABMs and their typical and correct use rates for preventing pregnancy, reflected in high quality, prospective studies that follow individual methods of fertility awareness.

These figures are a much better reflection of the science than the 25% failure rate most frequently quoted for FABMs. That statistic is wrong on so many levels that we could write  a whole article about it. So we did!

Five reasons why FABMs are more effective than 75%

1. This number comes from patient recall, not prospective studies. The oft quoted 25% failure rate, taken from a 2011 article by James Trussell, is based on estimates of the probability of pregnancy taken from the 1995 and 2002 retrospective National Surveys of Family Growth (NSFG).(²⁾ That is, researchers contacted a few thousand women with unintended pregnancies and asked them to recall which family planning method they were using at the time they got pregnant.  These retrospective surveys based on patient recall(³⁾ are of lower quality than the prospective cohort studies like the ones studied here.
2. Rates for all FABMs or NFP methods were pooled. Quoting a combined typical use effectiveness rate for all FABMs masks important differences between methods. This would be akin to quoting a combined effectiveness rate for all forms of birth control that only contain progesterone, such as the IUD and the mini pill. It is an inaccurate reflection of the effectiveness of individual methods. As seen in the table above, both the correct and typical use rates vary depending on the method since the required observations and guidelines for use differ as well.
3. These rates were adjusted to account for an underreporting of abortion to generate an estimated unintended pregnancy rate. Again, this is the difference between a prospective study, that follows specific users throughout a period of time, and a patient recall study.
   
4. 86% of the users surveyed in the NSFG identified the calendar rhythm method—a much older and less effective method—as their primary form of contraception.(⁴⁾   Again, this “lumping together” of all FABMs including “rhythm” masks important differences in effectiveness among the variety of modern methods(5); a fact acknowledged by the author of this estimate.(5)
5. Intention and motivation are more nuanced for FABMs than for contraception. Contraception can only be used one way: to avoid pregnancy. FABMs can be used to either avoid or achieve pregnancy. If a woman has sex during her fertile days, it is difficult to prospectively assess each month if she was aware that she was using the method knowing the risk of pregnancy, or if she didn’t understand the method.

What are the true effectiveness rates?

We propose it would be more accurate to cite the effectiveness rates for the individual methods based on the best prospective studies available. In 2013, we published a review of studies on fertility awareness based methods (FABMs) that had been published in peer reviewed journals since 1980.(1)

Based on studies with the best evidence (Level 1), we found that for individual FABMs, correct use effectiveness rates ranged from 95.2% – 99.6%. Typical use effectiveness rates ranged from 85.8% – 98.4%. That is, depending on which FABM a couple uses, the unintended pregnancy rate with typical use ranges from as low as 2% for the sympto-thermal method to 14% for the Two Day Method. This range does not reach nearly as high as 25%, which is often quoted by the media and even medical organizations.

Motivation and training are key

Just as with any method of family planning, there is a difference between method effectiveness (perfect use) and typical use. When you have a strong reason to avoid pregnancy, how can you be sure you or your patient is achieving the highest effectiveness rates using of your chosen FABM?

1. Be motivated. This first point can’t be articulated enough. Motivation is crucial to the success of those using a FABM, and what could be more motivating than understanding the risks of a serious birth defect? Similar to how high levels of effectiveness for the Billings Ovulation Method were seen in very motivated populations in the People’s Republic of China, so too can FABMs be very effective for couples who understand the risks of conceiving while the Zika virus is still unknown.
2. Seek accurate training. To use FABMs most effectively, women require accurate information about how to observe their signs of fertility and the guidelines they should follow if they wish to prevent pregnancy.  Likewise, they deserve accurate information about the actual effectiveness of the specific method they choose to use based on the best evidence available.

As you can see, the effectiveness rates of FABMs are comparable to the most commonly used forms of birth control.  Therefore, if you or your patients are interested in using FABMs, please get accurate information.  Also, to make sure women or couples can use these methods most effectively, it is always best to refer them to a trained instructor in the method of their choice.  For more information about the best evidence supporting the use of FABMs, please visit our website: FACTSaboutFertility.org and always encourage your patients to contact their educators in order to achieve the highest effectiveness cited here.

References

1. Manhart MD, Duane M, Lind A, Sinai I, Golden-Tevald J “ Fertility Awareness-Based Methods of Family Planning: A Review of Effectiveness for Avoiding Pregnancy Using SORT. Osteopathic Family Physician 5, 2-8, 2013.
2. Trussell J, “Contraceptive Failure in the United States”   Contraception 83(5): 397-404, 2011.
3. Mosher WD, Jones J: “Use of Contraception in the United Stats: 1982-2008. National Center for Health Statistics.” Vital Health Stat 23 (29), 2010
4. Vaughan B, Trussell J, Kost K, Singh S, Jones R “Discontinuation and resumption of contraceptive use: results from the 2002 National Survey of Family Growth” Contraception 78:271-283, 2008.
5. Lamprecht, V, Trussell, J “Natural family planning effectiveness: Evaluating published reports.” Advances in Contraception 13(2/3): 155-165, 1997.

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