Methods of Natural Family Planning

A (brief) critical overview

As I’ve been saying repeatedly (incessantly?), the week that has now drawn to a close has been National NFP Awareness Week, coinciding with the anniversary of Pope St. Paul VI’s encyclical Humanae vitae. And, as I’ve been saying, it is the clear teaching of the Church, in Humanae vitae and elsewhere, that it is virtuous (prudent, just, and chaste) and holy for couples to make use of natural family planning to avoid procreation when they have a serious reason - health, economic, or social - for doing so. I have mentioned very briefly that natural family planning (NFP) involves ascertaining the fertile time of the woman’s cycle and then, when the couple is trying to avoid pregnancy, abstaining from intercourse during this time. I assume that most of my readers already know this. I have not yet written about how this is done. Now, as it happens, there are many NFP methods - many methods for ascertaining the fertile time of a woman’s cycle. These vary greatly in what they “look at” in order to do so. And while I’m confident that many of my readers are familiar with one or more of these methods, I suspect that some of my readers aren’t, and that most of my readers are not deeply acquainted with the full range of NFP methods. I think that it is good to have some awareness of the variety of methods that are available - of what they are, how they work, and what we do, and don’t, know about their effectiveness - both so that one can make an informed choice about what method to use in one’s own marriage if applicable; and so that one can be confident that the Church’s teaching about the use of NFP - and not contraception - to regulate procreation when there is good reason is not a pure abstraction with no actual applicability. One should, that is, know that there really is such a thing as a workable and effective method of NFP - and indeed should know, concretely, what such a method is.

My goal in this article is to provide an overview of some (not all - there are too many nowadays) representative NFP methods (capturing the main categories, as I will explain). Two caveats are in order. First, I am not going to get deeply into the technical details of any of the methods. Apart from the fact that doing so would be beyond my scope today, this is primarily for the simple reason that I am not qualified to do so. I am not an NFP teacher. If you want to find NFP instruction, the USCCB can help, and I will also mention a couple of other, specific resources along the way. Second, this is going to be - as the subtitle of this article says - a critical overview. That is, I am going to offer some judgments about which methods are better and which are worse, based on both effectiveness and ease of learning/use. I think that this is important in any case, and all the more so because, to be brutally honest, there is some hype surrounding some of the methods. But NFP is health care, and health care should not be driven by hype. I think that it is important to cut through the hype.

I will note, in fact, that St. Paul VI specifically calls on medical scientists to develop good NFP methods (and he is not the only pope to do so). It follows that NFP methods should be scientific. They should be part of science- and evidence-based health care. When proponents of one or another NFP method hype their favored method in a way that does not reflect the scientific evidence, this is at odds with the mind of the Church.

Let me begin, then, by talking about what categories of NFP methods there are. The way that I am going to do this is by enumerating the ways in which the fertile time in a woman’s cycle can be determined. There are three main ways of doing this, and NFP methods can be categorized based on which of these ways they employ. The three ways are as follows.

1. It is possible to arrive at a rough determination of a woman’s fertile period through the use of statistics about when the average woman ovulates during her cycle. The earliest NFP methods made use of these statistics. Such methods are called calendar methods - or, as they were famously termed when they were developed in the 1930s, “rhythm methods.” There are two sub-categories of calendar methods: fixed- or standard-day methods, which assume that all women are fertile on the same range of days in every cycle; and variable-day methods, which employ a formula that an individual woman uses to determine her range of fertile days based on her range of cycle lengths. When a couple using a calendar method want to avoid pregnancy, they abstain from marital intercourse on the days that correspond to the fertile period as determined by the method’s instructions.

2. Later, it was discovered that there are fairly easily observable changes in a woman’s body that reliably correlate with the fertile time, because they are caused by the same hormonal changes that cause fertility. These are referred to as signs of fertility. There are two main signs of fertility: basal body temperature (BBT), and cervical mucus (CM). Taking BBT first: very nearly on the day of ovulation, a woman’s BBT increases slightly but measurably, and so starting a few days after the BBT shift, the woman is likely no longer fertile (the egg is no longer able to be fertilized). With regard to CM, the amount and type that is produced varies during the course of the woman’s cycle, and CM methods teach a woman to determine her fertile time by observing the quantity and quality of her CM each day. In addition to BBT-based methods and CM-based methods of NFP, there are also combination or multiple-indicator methods, which use both.

3. Most recently, electronic fertility monitors have been developed that measure levels of reproductive hormones (or their metabolites), like estrogen (or its metabolite E3G) and luteinizing hormone (LH), in a woman’s urine. Initially, these monitors were developed to help couples achieve pregnancy, and their use for this purpose - to facilitate fertility-focused intercourse - is fairly straightforward. Using them to avoid pregnancy is less straightforward, because (and the reasons for this are more complicated than is within my scope here) even when a monitor indicates low fertility - even when it indicates that a day is one which a couple would not want to make a special point of targeting for intercourse when trying to achieve pregnancy - that does not mean that the woman is not fertile. Therefore, it was necessary for researchers to develop protocols for the use of these fertility monitors to avoid pregnancy. The result has been fertility-monitor based NFP methods.

The reader will note that I am repeatedly speaking of “methods” - plural. Not only are there multiple categories of NFP methods, there are multiple methods in each category, and, in some cases, in each subcategory (especially those using signs of fertility: BBT, CM, and multiple-indictor). So, just for example, CM methods include the Billings Ovulation Method and the Creighton Model.

How effective are the various methods? Happily, a 2018 systematic review of peer-reviewed effectiveness studies of NFP methods was published in the journal Obstetrics & Gynecology, thus saving us all the work of having to do a literature search for ourselves to find out what is really known - not hyped, but known - about how well the methods work. As you’ll see if you click on the above link, the full text of the article is behind a paywall. You can find a very brief summary of the review’s findings in the section that is displayed on the linked page (prior to the paywall). However, this summary collapses multiple studies of some methods into one effectiveness number (or rather range of numbers). So, I’m including here screenshots of two key figures from the body of the article (I have the article on my drive), which show the findings of individual studies. Figure 2, as indicated by the caption, shows “typical use” effectiveness; figure 3 shows “perfect use” effectiveness.

I’m not going to go through these findings and comment in detail on each and every one of them, but I am going to point out several things, perhaps somewhat at random.

First, I want to note that one well-known method is not represented here, namely, the Creighton Model. This is because the published effectiveness study of the Creighton Model uses a statistical methodology that is, to put it kindly, idiosyncratic. To put it less kindly, I would go so far as to say that it fudges things to make the method look more effective than it really is. It “counts” what any other researcher would call attempts to avoid pregnancy as attempts to achieve pregnancy, so that when pregnancies occur in such cases, this is counted toward rather than against the method’s effectiveness. In any case, whatever one thinks of this as a matter of science or ethics, the result is that trying to compare the Creighton Model study with any study of the effectiveness of any other NFP method would be like comparing apples and oranges. Therefore, the authors of the systematic review had to leave the Creighton Model out. Additionally, I will note, the Creighton Model is quite onerous to learn and to teach. I have seen the worksheet that details what cervical mucus observations women using the Creighton Model have to make - multiple times a day. And when I say “details,” I mean details (the woman has to categorize her cervical mucus in literally a couple of dozen ways each time). Yet, we simply don’t know whether this results in good effectiveness. For all that we know, the Creighton Model involves a lot of work for, at best, no more reward than other methods. To be blunt, I think it should be declared obsolete at best. Those who want to learn - or teach - a scientific method should look elsewhere.

Second, there are also, it seems, no effectiveness studies of the variable-day method. So, is it better than the standard-day method? We simply don’t know.

Third, the Billings Method, popular and heavily promoted as it sometimes has been, simply doesn’t work very well.

Fourth, interestingly, the standard-day method - the simplest possible NFP method - is about 85% effective with typical use and about 95% effective with perfect use! This is the method that many people think of when they think of NFP, when they are wholly unaware of methods that use signs of fertility or fertility monitors - and that has sometimes been dismissed as very ineffective, even called names like “Vatican roulette.” Now, is 85-95% effectiveness “enough” for all couples needing to avoid pregnancy? No. It is very important that scientists have sought to develop more effective methods - and, as we’ll see, have succeeded in doing so. There are couples - for example, those with health reasons for avoiding pregnancy - for whom another pregnancy “now” would cause major problems, and who therefore need these newer and better methods. However, there are also couples whose serious reason for avoiding pregnancy is of a different sort, such that, while it is important that they have fewer total babies during their reproductive years than they would likely have if they didn’t use NFP - put differently, that the average spacing of their pregnancies be greater than it would be without NFP - nevertheless, having a baby sooner than intended once or twice during their reproductive years would not be catastrophic. I am thinking, for example, of some of those couples whose serious reasons for NFP use are economic ones. For such couples, a very simple method - one that can literally be learned in minutes and requires only a calendar and a pencil to use - and that is 85-95% effective might be just right. I will also note that, for those who don’t want to bother with a calendar and a pencil, none other than the Georgetown University Institute for Reproductive Health has developed a version of the standard-day model called CycleBeads.

Fifth, the two most effective methods are the Marquette Method (formerly Marquette Model) and Sensiplan. The Marquette Method was developed at my three-times alma mater, Marquette University, specifically at its College of Nursing Institute for Natural Family Planning. Full disclosure: I am on its board of advisors, and also on the board of directors of the related Marquette Method Professionals Association; additionally, the founding director of the Institute is an old and dear friend. The Marquette Method is primarily a fertility-monitor method, though users can learn to incorporate observation about signs of fertility as well. The researchers at the Institute are working on developing protocols for situations in which other NFP methods can be very difficult to use, such as the postpartum/post-breastfeeding transition, and perimenopause. Sensiplan was developed in Germany, at the request of the German bishops, and is a multiple-indicator method, combining BBT and CM observations. I recommend that couples who need a highly effective NFP method use either the Marquette Method or Sensiplan - and that those who want to teach an NFP method that has the best peer-reviewed research validation pursue training in one of these methods. I will note that in order to become a Marquette Method teacher, one must be a health-care professional - nurse, physician assistant, physician, pharmacist, …

This concludes my series of articles for NFP Week 2024. My prayer for all the married people among my readers is that they will find happiness and holiness in their vocation. And ask me about NFP!

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Ceterum autem censeo Putin et Cyrillum esse deponendos.