Natural Family Planning International, Inc. (NFPI)
Home NFP Resources Spiritual Resources Blog Contact


Question. I have a question about this contraception method called NFP. I don't understand: if this method REALLY works, then how come not many people know or use NFP? I heard that people in less developed countries such as Mexico, India, or Africa use this type of contraception, but that means NFP does not work. I heard that Pearl-Index of NFP shows a 98% effectiveness rate, but some claim that this is not a reliable data. I really need a source material that proves this contraception DOES work.
-MTC, Japan

Response. First, we do not consider NFP to be a method of contraception-against conception-because it does nothing to prevent conception from the normal sexual act. Systematic NFP is a system for determining the limits of the fertile time. Couples seeking to achieve pregnancy thus know the best time to engage in the marriage act. Couples wanting to avoid pregnancy know the days on which they need to abstain from the marriage act.

The effectiveness of natural family planning as a method for avoiding pregnancy is related to the type of NFP that is used, how well it is taught, and how well the couples follow the rules. The most recent study of the Sympto-Thermal Method was published in February, 2007 ("The effectiveness of a fertility awareness based method to avoid pregnancy in relation to a couple's sexual behavior during the fertile time: a prospective longitudinal study" by Petra Frank-Herrmann and others, Human Reproduction, advance notice on February 21, 2007). Here the German researchers found a "perfect-use" effectiveness rate of 99.6%. "Perfect-use" means that the couples followed the rules in every cycle. Those who cheated by using condoms during the fertile time had a slightly lower effectiveness rate of 99.4%, but that's not NFP. Another rate-the overall user-effectiveness rate-includes all the pregnancies from all the participants whether they used the method properly or not, whether they abstained during the fertile time or not. That rate was 98.2%. Such a high overall user rate is unusual, but in this study the couples who engaged in the marriage act during the fertile time abstained during the most-fertile days and had relations only at the margins of the fertile time.

The bottom line is that modern systematic NFP methods are highly effective when couples follow the rules. In almost every study, a certain number of couples apparently decide they really don't have any serious reason to avoid pregnancy, so they don't follow the rules and thus reduce the "typical" or "overall user" rates of effectiveness.

I have no knowledge about the teaching of natural family planning in Japan. Your English is good; I think you can teach yourself how to use NFP from the NFP-How-to manual on our website. -JFK

Q. The German study by Frank-Herrmann and others published in February 2007 found a 99.6% "perfect-use" effectiveness rate for their version of the Sympto-Thermal Method. How do their rules compare to the rules in your online manual, Natural Family Planning: The Question-Answer Book?

R. To determine the End of Phase One, the Frank-Herrmann study used what we call the Day 5 Rule for the first 12 cycles. Our online manual also uses a Day 6 rule. After 12 cycles, they used a conservative variation of what we call the Doering Rule. They said to subtract eight days from the earliest day of temperature rise in the preceding 12 cycles and to call that day the last day of Phase One. Our manual says to subtract seven days. Both of their rules are subordinate to the presence of cervical mucus. Our manual also provides the Last Dry Day Rule; their study did not allow this rule. In fact, they noted that in another study, all of the unplanned pregnancies (very few) resulted from the use of the Last Dry Day Rule. Thus this study used more conservative End-of-Phase-One rules than we have used for years and have published in the online manual. To determine the First Day of Phase Three, the time of post-ovulation infertility, the Frank-Herrmann study used a rule very similar to what we call Rule R with one exception. Both rules call for the third day of higher temperature readings to be at least 0.2 degrees C. (0.4 degrees F) above the six readings that make up what we call the Low Temperature Level. However, their rule does not state any minimum amount of elevation for the first two rising temperatures, while Rule R states that all the readings must be at least 0.2 degrees F above the Low Temperature Level.. Thus, compared to our online manual, this study used a slightly more liberal rule for the start of Phase Three.

Q. We took a chance and became pregnant. I have a history of long cycles and thought I hadn't ovulated before Day 17 in previous cycles. On Day 12, I had just started having thick mucus that I hoped was infertile mucus. The cervix was still low and just starting to open. So we took a chance and bet we were still infertile.

R. Your experience is not unique. We do not use the term "infertile" mucus. Instead, we use the terms "less fertile" and "more fertile" to describe different kinds of mucus. Your mucus is "infertile" only if you are in Phase Three, the time of post-ovulation infertility, and that does not apply when you are in a pre-ovulation phase of the cycle. Our conviction has long been that if the mucus is fluid enough to flow out of the cervix, it is also fluid enough to admit sperm migration. Also, if the cervix is starting to open, that's a sign that your ovulation-causing hormones are at work.

Sometimes improved nutrition can help produce cycle patterns that are closer to the "normal" cycle of around 26 to 30 days. We recommend Marilyn Shannon's book, Fertility, Cycles and Nutrition. It's featured in Books.