47

The Creighton Method of natural family planning claims to have a 3.2% failure rate for typical use, and a failure rate of 0.5% for perfect use. However, my primary care doctor said that Natural Family Planning in general has a low success rate. This has immediately raised a red flag for me about the veracity of the Creighton Method's claim. Thus my question is:

Question

If used perfectly (or "typically"), does the Creighton Method of Natural Family Planning fail only 0.5% - 3.2% of the time?

85

In 2018, my colleagues and I published a comprehensive systematic review examining the extent and quality of evidence on all fertility awareness based methods (FABMs) for pregnancy prevention for which effectiveness studies have been published. That systematic review is available here: https://journals.lww.com/greenjournal/Abstract/2018/09000/Effectiveness_of_Fertility_Awareness_Based_Methods.8.aspx. We identified 53 relevant studies. Of them, 0 were ranked high quality, 21 were ranked moderate quality, and 32 were ranked low quality for our question of interest. The systematic review focuses on estimates from moderate quality studies, since no high quality studies on this topic were identified at the time of the review.

A few months ago, I also co-authored a summary piece in BMJ, which provides an infographic summarizing results of the systematic review. The BMJ piece/infographic can be found here: https://www.bmj.com/content/366/bmj.l4245.

Regarding your question on the Creighton method, I'd refer you to this paragraph in our systematic review:

We identified three mucus-based Creighton Model studies and one meta-analysis, all conducted in the United States and Canada. Two studies and the meta-analysis did not provide standard typical use pregnancy estimates. Instead, in these three analyses, pregnancies occurring as a result of intercourse on a day identified by the woman or the couple as fertile were classified by investigators as caused by “achieving [pregnancy]-related behavior.” Achieving-related pregnancies thus included both intended or planned and unintended or unplanned pregnancies, and all these pregnancies were excluded from the effectiveness estimates. By excluding most unintended or unplanned pregnancies from effectiveness calculations, these studies underestimate pregnancy probabilities relative to standard typical use calculations, potentially quite substantially. We considered this type of calculation low quality evidence related to the question of typical use effectiveness. One additional Creighton study provided a standard typical use pregnancy estimate in addition to the described approach but was ranked low for other reasons. In addition, perfect use pregnancy probabilities were incorrectly calculated in these studies (eg, using all cycles in the denominator rather than only perfect use cycles).

I hope that helps to answer your question.

  • 24
    Thanks for clarifying. So, if I'm understanding right; the Creighton studies excluded unplanned pregnancies from their "effectiveness" statistic when they were due to couples having sex when they were fertile?? Isn't that... kind of the point of a "typical use" estimate? Just like "typical use" for condoms includes all the times you didn't have one or didn't bother? – BradC Sep 30 at 21:00
  • 23
    Yes, the approach used in most Creighton studies is highly unusual, and not reflective of how effectiveness estimates are calculated for other methods of pregnancy prevention. This is part of the reason why we considered estimates from the Creighton studies to be "low quality" for our question of interest in our systematic review. – cpolis Sep 30 at 21:08
  • 1
    Very nice infographic on BMJ! For that chart, is "Creighton" grouped as a variation of the "Billings Ovulation Method"? Or is not included, due to the lack of quality studies for that method? – BradC Sep 30 at 21:27
  • 8
    So glad you found the infographic useful! We really enjoyed working with the talented interactive data graphics designer (Will Stahl-Timmins) at BMJ on it! To your question, Creighton studies are excluded from the infographic (and summary results of our systematic review, upon which the infographic is based), since all Creighton studies we identified were ranked "low quality". We describe this in the systematic review - a pdf is freely available here if of interest: replyobgyn.com/wp-content/uploads/2019/01/…. – cpolis Sep 30 at 21:59
  • 7
    Contraceptive effectiveness is calculated using two measures: perfect use and typical use. Typical use estimates incorporate method failures AND pregnancies stemming from users not using the method correctly and consistently (like pregnancies from forgetting to put a condom on). For perfect use, only pregnancies stemming from correct and consistent use are counted. The difference between typical and perfect use estimates reveals the consequences of imperfect use, and depends on how unforgiving a method is of imperfect use and how hard it is to use that method perfectly. – cpolis Oct 2 at 2:48
32

3.2% sounds somewhat good, but notice that the quoted failure rates are per year, not per couple.

For a couple using this method, over a ten year period, there is a 28% chance of at least one pregnancy, over twenty years it is 48%, and over twenty-five years it is 56%.

100% - (100%-3.2%)¹⁰,   100% - (100%-3.2%)²⁰,   and 100% - (100%-3.2%)²⁵

So, even if the 3.2% value is reliable, the method itself isn't a reliable means of preventing pregnancy.

It is a reliable way of reducing pregnancies though, for couples that want to have small families.

  • 14
    This is nice additional information, but I think a full answer to the question should check if the 3.2%/0.5% are reliable in the first place. – tim Sep 30 at 14:50
  • 12
    And if we are looking at context, it would be helpful to look at failure rate of other birth control. Condoms eg have a "perfect use" failure rate of 2%, and a "typical use" failure rate of 18% (though afaik "typical use" here also includes not using a condom; the cdc where the data is from puts "typical use" failure rate of "fertility-awareness based methods" at 24%; given this data, even 3.2% seems rather low) – tim Sep 30 at 14:51
  • 7
    See response below regarding concerns about the Creighton estimates. Also, best to avoid the assumption that 12-month typical use failure rates are consistent over longer time periods (as done above). This likely results in overestimates of typical use failure rates, since the most fertile & least adherent users become pregnant, leaving behind a group that over time is less likely to fail. Regarding CDC FABM rates, they recently updated this (see cdc.gov/reproductivehealth/contraception/index.htm). They cite a systematic review I described below & Contraceptive Technology book. – cpolis Sep 30 at 23:03
  • 3
    The calculations are based on implicit assumptions that are unreferenced (and, in fact, wrong). – Oddthinking Oct 2 at 1:11
  • 2
    This similar question addresses how the simplistic modelling done in this answer does not map to reality. – Oddthinking Oct 2 at 21:45
17

The Creighton Method of NFP is fairly effective, but in lab research not quite as effective as the market copy with perfect use.

Use effectiveness of the Creighton model ovulation method of natural family planning

RESULTS:
At 12 months of use, the Creighton model was 98.8% method effective and 98.0% use effective in avoiding pregnancy. It was 24.4% use effective in achieving pregnancy. The continuation rate for the sample at 12 months of use was 78.0%.

CONCLUSION:
The Creighton model is an effective method of family planning when used to avoid or achieve pregnancy. However, its effectiveness depends on its being taught by qualified teachers. The effectiveness rate of the Creighton model is based on the assumption that if couples knowingly use the female partner's days of fertility for genital intercourse, they are using the method to achieve pregnancy.

My wife and I use the Creighton method. We asked our teacher about the disparity between the two figures, and were told that part of it is the same problem that most birth control methods have, that one or both parties might intentionally or unintentionally fudge the results. The Creighton Institute adjusts their figures based on data from the teachers, who are more likely to be told by one of the users that the intentionally misread a chart because they want a child, or that they'd been following the method exactly except for that one vacation where they filled it in afterwards and might have shaded towards assuming that they were not fertile even though the signs were there.

For what it is worth, the Creighton Institute's figures are available in a chart here.

"Creighton Model Method and Use Effectiveness to Avoid Pregnancy by Center, 5-Study Composite and Ordinal Month of Use"

Regrettably, it doesn't look like anyone has published results of a study of efficacy since the late 1990s. And, of course, you run into the same issues as in Does natural family planning decrease divorce rates? where the demographic who uses the method are heavily skewed toward one end.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .