Just How Effective is Natural Family Planning, Anyway?

One of the major arguments surrounding natural family planning is on its effectiveness. Critics of NFP claim isn’t all that effective at family planning. In part, this misconception is due to two things:

Charles Auguste Romain Lobbedez, Family Time (1876)

that, despite its name, it

1. There are a wide variety of practices thrown together under the name “NFP.” If you threw every means of contraception together (from sterilization to withdrawal), you would end up with accurate-but-virtually-meaningless statistics. So it is with NFP: the “Standard Days” method is far less accurate than the sympothermal method. By far less accurate, I mean that even when used perfectly, it results in more than ten times the number of unplanned pregnancies (5% v. 0.4%). So when you hear a generic number about “NFP effectiveness,” realize that it might be including some fairly unreliable methods.
   
   
2. Couples that practice NFP tend to want, or at least be open, to large families. In other words, the overlap between “couples who use NFP” and “couples who don’t think of children as diseases to be prevented” is substantial. So unsurprisingly, NFP-practicing couples tend to have large families. That looks like a bug, but is a feature (after all, many couples use NFP to have more children, not fewer).

Because of reason # 1, there are misleading (and imprecise) statistics on NFP effectiveness. Because of reason # 2, there’s a lot of anecdotal evidence leading people to think that NFP means large families, and therefore (the assumption goes), NFP mean lots of unplanned pregnancies.

So what are the real statistics?

Lets turn to two sources. First, “Contraceptive Failure in the United States” by James Trussell of the Office of Population Research at Princeton University. Trussell has a helpful chart (page 398 of this PDF) showing the unplanned pregnancy rate per year of a wide variety of family-planning methods, including all sorts of contraception and NFP.

From this chart, we see that sympto-thermal NFP, when used perfectly, was about as effective as the the Pill (0.4% and 0.3% unplanned pregnancy rate, respectively), and far more effective than either male (2%) or female (5%) condoms.

The only shortcoming to Trussell’s work is that it only lists the “perfect-use” percentages for each specific form of NFP. So while he tells us that typical use for the Pill involves 9% of women getting pregnant within a year, along with 18-21% of women relying on condoms, we don’t have a way to directly compare that with typical use symptothermal.

Fortunately, he cites to a large-scale study examining the topic. This study found that symptothermal NFP, when used perfectly, resulted in an annual 0.4% pregnancy rate. Overall, the typical-use rate was 1.8%. Even for women who had “unprotected” sex during their fertile period, the pregnancy rate was only 7.8% (since these couples tended to avoid the earliest, and most fertile, part of the woman’s fertile period). [Here is the study, and a very-readable summary of it.]

Comparing NFP to the major forms of contraception directly, here’s what we see:

“% of women experiencing an unintended pregnancy within the first year of use”
	“Typical Use”	“Perfect Use”
Combined pill and progestin-only pill	9%	0.3%
Female condoms	21%	5%
Male condoms	18%	2%
Withdrawal	22%	4%
Symptothermal NFP	1.8%	0.4%

Other studies appear to confirm similar effectiveness for the Creighton Method (1.2% perfect use; 2.0% typical use). The statistics paint a clear picture. When it comes to family planning, symptothermal NFP typically is far more reliable than condoms or the Pill.

So even apart from moral justifications, NFP produces the same results or better, without the risk of horrible side effects accompanying many forms of contraception. For example, many contraceptives carry the risk of preventing pregnancy for years after use: in short, they work too well at inhibiting fertility.

To take another case, the European Union has called for a $47 billion clean-up plan to purify the water system in the United Kingdom, after it was revealed that ethinyl estradiol (the primary ingredient used in birth control pills) was leading to intersex fish, and collapsing fish populations. So these drugs are unhealthy and unsafe for a fish to ingest, yet our culture has convinced women to poison their bodies with them. As a result, everyone who drinks the water is at risk. Given that these pills aren’t substantially better at preventing pregnancies than NFP (in theory or in practice), this is all the more tragic.

The Other Implications of NFP Effectiveness

Ary Scheffer,
Faust and Marguerite in the Garden (1846)

So NFP advocates are right: natural family planning really does work at family planning. But that only accentuates the need for NFP not to turn into the “Catholic-friendly contraception” that its critics claim.  Certainly, there’s nothing wrong with being responsibility about your sexuality. On the contrary, all human actions demand prudence, and a life-changing action like sexual intercourse calls for far more prudence than preparing dinner or determining the shortest route to the bank.

There is no virtue in treating your sexuality in an animalistic way. As Pope Paul VI noted in paragraph 10 of Humanae Vitae: “With regard to man's innate drives and emotions, responsible parenthood means that man's reason and will must exert control over them.” And Pope Pius XI, back in 1930, acknowledged that this “virtuous continence” was permitted in matrimony, as long as both parties consent. So being responsible about your sexuality is virtuous, and even necessary.

But a virtue is the mean between two extremes: and just as you can be reckless about your sexuality, you can also be obsessively controlling. An over-reliance on NFP to space or prevent the creation of new life can close its practitioners off to life. Worse, it can be symptomatic of an unhealthy approach to life in general: a need for more control than is warranted.

In the discussion of why NFP is okay when contraception is not, in paragraph 16 of Humanae Vitae, Paul VI explained that it was to be used only for good reason:

If therefore there are well-grounded reasons for spacing births, arising from the physical or psychological condition of husband or wife, or from external circumstances, the Church teaches that married people may then take advantage of the natural cycles immanent in the reproductive system and engage in marital intercourse only during those times that are infertile, thus controlling birth in a way which does not in the least offend the moral principles which We have just explained.

NFP was never intended to be the normal or ideal way that Catholics engaged in the marital act. It’s not healthy, virtuous or wise to obsess over NFP, particularly when one has the resources to welcome another child.

My concern is that NFP seems to be presented as the normal or ideal way that Catholics should approach their sexuality. And without a doubt, it’s far better than contraception. Back in 1880, the Sacred Penintentiary confirmed that “a confessor may, with due caution, suggest this proposal [avoiding intercourse during fertile periods] to spouses if his other attempts to lead them away from the detestable crime of onanism [that is, the “withdrawal” method] have proved fruitless.” So if the choice is between contraception (which is sinful), and NFP (which isn’t), easy choice.

But if the choice is between NFP and simply being open to new life without trying to make a plan, the latter is even more ideal. NFP has never been the ideal way to approach human sexuality, and if you find that you’re over-reliant on it (particularly if you have the resources to welcome another child), it might be time to take a step out in faith, and trust God not to give you more than you can handle.

Update: The second section above is intended to refer to using NFP to prevent pregnancy. I’ve modified one of the sentences to eliminate ambiguity on this point.