Tuesday, May 28, 2013

NFP: How Much Abstinence?

A reader asks the following about Natural Family Planning:

I have heard the average of Phase II being 12 to 14 (at least, on the NFP forums I am involved in).

I think 10 days is quite unusual, and quite "lucky" in the NFP world. Or, you are just more "open" to children than others. :)

When I read West or Popcak say "7 to 10", I just shake my head.

How much abstinence?

A common question about Natural Family Planning is how much abstinence should couples expect. Some couples ask "What's so hard about a week off?", while others reply "A week? Try two or more!"

It is also a question that few NFP advocates address. 


This post deals with Phase II abstinence only. Some couples may abstain more during Phase I, but such abstinence is too variable and personal to address in a post. Some couples may be comfortable with sex during menstruation, others may not be. The decision to abstain during menstruation is a personal choice, not one required to avoid pregnancy or follow Church teaching. (Yes, I know the Billings/Creighton rule, but it remains low risk.) Some couples may be strict about the "every other day" rule, while others may feel confident enough about their observations to use every day.

This post only deals with non-postpartum cycles in a healthy, cycling woman. Some cycle disorders, such as PCOS, can cause the fertile period to seem unusually long. In reality, a woman with PCOS is subfertile and these days are simply false-positives. Also, cycles may be unusual postpartum. Extended abstinence is not uncommon in these situations.

Finally, every woman is different and every cycle is different. "Normal" for one woman may not be "normal" for another. Even if a woman usually has "normal" cycles, this is no guarantee that every cycle will be "normal"

The Fertile Window

The actual "fertile window" where sex can lead to conception is only a maximum of 6 days.

Among healthy women trying to conceive, nearly all pregnancies can be attributed to intercourse during a six-day period ending on the day of ovulation.
Ovulation = Day 0


Sperm live for a maximum of five days (in good cervical fluid) and the egg lives for no more than one day. 5 + 1 = 6 days of fertility. Conception is most likely on the day of ovulation and the two days before.

Method Days of Possible Fertility

Every method adds in some "margin of error" to make sure couples trying to avoid don't get pregnant. Additionally, methods must be able to predict ovulation from five days out and sometimes fertile symptoms last for longer than five days.

How many days do each NFP method mark as fertile, on average?

Symptothermal Method
According to one study of the Symptothermal Method, it's 13 days, less when you get more experience.
However, one has to realize that the median fertile time determined by the STM is 13 days a cycle (less days after the first year). The potential fertile time is in fact longer than the actual physiological fertile time.
This particular Symptothermal Method did not have a basic infertile pattern (Yellow Stamp) instruction, instead, it considered the "Last Dry Day" to be the end of Phase I. Common sense says that it may take more time for two fertility signs to coincide than only one. (Our own experience is that the temp shift tends to be later than the mucus dry-up.)

Many couples were aware that the method was conservative and used days of possible fertility at the beginning and end of Phase II without getting pregnant.

Billings Ovulation Method

Another study found an average of 10 days of possible fertility with the Billings Method.

Billings has generally has a higher overall pregnancy rate than STM, which makes sense. (Less abstinence=less margin of error.)

Billings instructor Kristin Putnam claims 6-8 days of possible fertility is normal and anything MORE than this is a sign something may be wrong, such as a hormonal or nutritional issue.

We ended up taking classes from her and were able to reduce our abstinence as a result. We were very pleased with this, but, as always, YMMV.

Rae of No Wealth But Life/Vita Catholic claims a minimum of 9 days of abstinence for women of normal fertility and anything LESS than this is a sign of possible sub-fertility. Many of the commentators had similar experiences.

Rae also notes that fertility declines with age. While it may seem like abstinence lasts forever and an amorous look during Phase II can get you pregnant when you are in your mid 20s, when you are in your 30s, the observed fertile period may be shorter and the likelihood of pregnancy may be reduced.

Creighton Model Fertility Care

I have not been able to find any studies of Creighton Model (please provide studies in the comments if you have them), but because Creighton is a derivative of Billings (the rules are similar, but the observation techniques are different) then they should have about the same amount of abstinence. Anecdotally, this seems to be the case for most women.

A small number of women can use Billings, but not Creighton and a small number can use Creighton, but not Billings. Obviously, for these women, the methods will provide very different results.

Marquette Method

I am not aware of any studies on the length of the fertile window under the Marquette Method. (Please provide studies in the comments if you have them.)

The materials provided on Marquette's website note that the actual fertile window is 6 days.

In the charts provided in the user manual, however, the fertile window appears to be closer to 13 days. This is unsurprising because the official rules of the Marquette Method are very similar to the rules of Symptothermal in the Frank-Herrmann study cited above.

That being said, the fertility monitor gives many couples the confidence to days marked as fertile by the method, but not by the monitor, although this does increase the risk of pregnancy.


A recent study from Poland compared the Billings Method, Creighton Model, the Two-Day Method, various Symptothermal Methods, Rhythm, and Phase III BBT only. (Marquette Method was not included.) They also proposed a new symptothermal method (DBN) with the beginning of Phase II calculated by a computer algorithm.

They looked for the number of days available in a cycle and the number of "false negatives", that is, days in the 6-day fertile window that were marked as infertile. The results were as follows:

Not surprisingly, Billings (BO) and Creighton (CM) had the most available days and the highest percentage of false negatives (highest risk). Billings and Creighton supporters would counter that pregnancies resulting from intercourse on a day marked infertile within 6 days of ovulation are rare due to poor quality cervical fluid or poor follicular development, although they are certainly possible.

The various Symptothermal methods all had fewer false negatives, but fewer available days (more false positives).

To demonstrate the differences between methods, the following charts are for the same woman on the same cycle. (Intercourse markings have been removed):

Billings Ovulation Method = 8 days (CD 8-15)

Symptothermal Method (Fertility Awareness Method) = 13 days (CD 5-17)


Multiple studies have shown that the "fertile window" during which intercourse may lead to pregnancy is no more than six days long. Due to the difficulty in predicting and detecting ovulation,  methods of Natural Family Planning often consider days beyond those in the fertile window to be potentially fertile. Different methods take different approaches to calculating the potentially fertile window. Generally, methods that mark the least number of days as potentially fertile expose couples to the greatest amount of risk of possible pregnancy. Although all methods claim a low perfect-use failure rate when used to avoid pregnancy, the "actual use" pregnancy rate can vary widely. Methods with a shorter average abstinence period leave couples who want to avoid pregnancy with less of a margin of error.

In choosing a method of Natural Family Planning, couples should weigh their need to avoid pregnancy against the strain that extended abstinence will put on their marriage. A couple who does not have a very serious reasons to avoid pregnancy would be well-served by choosing a method with less abstinence or by using a more conservative method, like Marquette, less strictly. A couple who has a very serious need to avoid pregnancy can gain peace of mind by choosing a method designed for maximum security.


  1. An honest overview of the abstinence involved in using NFP! Every time I hear the 'only a week of abstinence' line I want to deck someone.

    It's also good to hear someone say that which is obvious but is not often said. Methods with a larger margin of error (more abstinence) will most likely be more effective.

    I like what you said about maybe being less conservative than a method officially calls for. There is a big difference between taking the risk of having sex during the wife's period, and having sex on her peak day, yet some methods simply say that if a couple is not diligently following every rule they are trying to conceive. I don't understand that all or nothing kind of thinking.

    1. I see you've read Rae's commentary on that. The all-or-nothing is mostly a Creighton thing.


      Some of the older CCL material takes a somewhat similar tone.

      I think this sort of all-or-nothing thinking is a carryover from older Church documents on the rhythm method. Rhythm was something you either used or you didn't, it had no use other than achieving or avoiding pregnancy, it gave women very little information about their bodies, and it was infamously frustrating and unreliable.

      Now that we have modern NFP, I think the ideal is to make the observations, get the information, then prayerfully decide how to act on it. (Chance of pregnancy vs. abstinence) In the Catholic context, NFP supposed to be more about self-awareness than a method of birth control.

  2. Great post on this! I think a lot of people want to follow their method to the letter and sometimes wonder why they don't get many days so its nice to have a fair overview of all the methods. I think the goal of any NFP method should be efficiency in having the most days available AND being effective in identifying fertile days. Sometimes it feels theres only emphasis on avoiding pregnancy in some methods.

    1. Thank you! Yes, available days are VERY IMPORTANT!

      As is ease of use. Better to have a simple method that couples can understand and will actually use than a more accurate, but complicated, method that is burdensome or confusing.