Your right to know: Relative Effectiveness

As mentioned previously in my comments about cervical mucus, the US Bishops established the Human Life Foundation in 1968 to support Humanae Vitae and to promote natural family planning.  In the Seventies there was considerable debate about the relative effectiveness of the mucus-only “Ovulation Method” (OM) and the cross-checking “Sympto-Thermal Method” (STM) which uses mucus, temperature and previous cycle history.  The Foundation persuaded the National Institutes of Health to run a scientifically sound study in 1976-1978 to compare the use-effectiveness of the OM and STM.

In the formal study, the investigators found an OM imperfect-use rate of 39.7 and an STM imperfect-use rate of 13.7 pregnancies per 100 years of use.  In other words, the OM had an imperfect-use “avoiding” effectiveness rate of 60.3% and the STM had an imperfect-use “avoiding” rate of 86.3%.  The OM group experienced six perfect-use pregnancies; the STM group experienced zero perfect-use pregnancies.  In the words of the final report, “Results of this study show the STM to be superior to the OM of NFP in terms of use-effectiveness.” (Wade et al., “A randomized prospective study of the use-effectiveness of two methods of natural family planning,” Am. J. Obstet. Gynecol. 141:368, 1981, p.375)

Toward the end of the final report, the authors wrote: “It is of interest that after couples were informed in August, 1978 that a statistically significant trend in the pregnancy rate between the OM and STM groups had been found, almost all of the STM volunteers continued in training, and virtually all of the OM volunteers requested to be, and were, thoroughly trained in STM” (376).

In brief, when the relative effectiveness of the mucus-only “Ovulation Method” and the cross-checking “Sympto-Thermal Method” was hotly contested, the US Bishops sponsored a study which found that the STM approach was superior to the OM approach.  Your have a right to know these things.   

 Still, some or many dioceses seem to ignore that part of the science of NFP and continue to promote the mucus-only approach as if there is no difference.

Another comparison.  In the effectiveness comparisons, not much attention has been paid publicly to the differences in the computation of effectiveness rates, and there is a big difference.  The question is this: “How should we count pregnancies that result from not following the rules?”

The terminology has evolved over the years.  In current terminology, “perfect-use” pregnancies refer to pregnancies of couples who became pregnant while following the rules.  “Imperfect-use” pregnancies refer to pregnancies of couples who became pregnant while not following the rules. That seems rather straightforward, and most people in the NFP movement have accepted that standard.

Most is not all.  Dr. Thomas Hilgers, author of the mucus-only “Creighton Model” and “FertilityCareTM” does not accept that standard.  He argues that when a couple engages in the marriage act at a time defined as fertile or possibly fertile according to the rules, the spouses are engaging in “pregnancy-achieving behavior.”  Well, certainly, but that is true for every method.  The rest of the NFP movement counts such pregnancies as “imperfect-use” pregnancies, but Dr. Hilgers does not.  The result is that there are relatively few “imperfect-use” pregnancies in his calculations, and that makes his system appear to be much more effective than it would be if he used the standard accepted by the rest of the NFP movement.

How can we tell?  In 1985, Joanne Doud, a teacher of the Hilgers system, reported a study in which she claimed a very high imperfect-use rate of 96.2%.  Fortunately, she also listed the number of pregnancies that the couples themselves regarded as unplanned.  Using those numbers, the imperfect-use effectiveness was only 67% (Joanne Doud, “Use-effectiveness of the Creighton Model of NFP,” International Review of Natural Family Planning, Vol IX, No.1, Spring 1985).  You have a right to know these things.

For purposes of comparing apples with apples and for credibility, the rest of the NFP movement accepts the statistical method used by the contraceptive birth control movement.  Few in diocesan administration, however, seem to pay attention to the fact that the Hilgers system calculates its user-effectiveness rates in a way that is not accepted or practiced by anybody else in the NFP movement.  Dioceses have paid thousands of dollars to have a single teacher trained in the Hilgers version of mucus-only without any comparative indication that his system is any better than the original Billings system or the cross-checking Sympto-Thermal Method.

What about seeking pregnancy?  There have been no comparative studies about couples using different NFP systems to achieve pregnancy, and thus there is no evidence that any system of observing and recording the mucus sign is any better for achieving pregnancy than that used in any other system.  Fertile mucus is fertile mucus, no matter how observed and recorded.  Further, certain types of impaired fertility may be successfully resolved simply by improvements in nutrition and lifestyle.

On the other hand, when there is a case of difficult infertility, it is good to know that Hilgers-trained doctors may be able to treat certain defects with surgery or other medical techniques in what he calls NaProTECHNOLOGY.  It is also important to know that there are some couples in which one or both spouses are infertile and whose only morally sound hope for a child is the adoption of a baby who needs their loving care.

JFK, September 15, 2013

Next week: Spacing effectiveness of breastfeeding



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