What We Do

/Effectiveness & Satisfaction

Starting a family is a BIG deal! We get it.

Serena’s Sympto-Thermal Method (STM) is effective for achieving or avoiding pregnancy.

Serena participated in an international study1 about the STM to avoid pregnancy. All study participants who used the method correctly and consistently obtained an effectiveness rating of 0.5 unplanned pregnancies in 100 women. In other words, 99.5% of the couples using the STM perfectly achieved their goal of avoiding conception. This rate matches the effectiveness rates published for hormonal contraception.

You’re probably looking for percentages and statistics to compare the effectiveness of NFP with the effectiveness of other more common birth regulation methods. Google and mainstream media will give you all sorts of statistics, but we want to first equip you to understand what it is that you will be looking at because the numbers aren't as straightforward as you may think! 

A small lesson on interpreting effectiveness and statistics:

Effectiveness statistics for birth control methods are expressed in pregnancy rates. Dr. Suzanne Parenteau, Serena’s Medical Advisor, explains reliable statistics cite results of actual research studies. In those studies, the scientific standards categorize unplanned pregnancies in 2 ways:

  • Typical Use: all unplanned pregnancies that occur during an effectiveness study, including those which result from incorrect or inconsistent use of the method
  • Perfect Use: pregnancies that occur even though the method was used correctly and consistently

Pregnancy rates are not simple mathematical percentages which consider only the number of pregnancies and the number of couples involved in a study. They also take into account the number cycles that every participating couple has contributed to the study.

Don't be deceived! Most methods of contraception only ever advertise and publish perfect use statistics when describing the effectiveness of the contraceptive. Do a quick search and see for yourself!

Effectiveness mainly depends on: a.) how well taught and understood the method is,  b.) how it is consistently used as instructed and  c.) the couple's motivation to respect the rules.

If a condom breaks or slips, this has consequences only if intercourse happens during the fertile window of a woman’s cycle. The condom is useless the rest of the time. If you’re using the STM and think to use a condom during the fertile time, you would not actually be reducing your chances of getting pregnant -- you would only be subjecting yourself to the failure rate of the condom. Effectiveness is not just based on the stats, it’s based on the stats and which part of the cycle you are in. Stats matter little if you are in the infertile part of your cycle.

Now, permit us to get a little more technical...

You may find it bizarre that pregnancy rates are used to describe a method's effectiveness for avoiding pregnancy. It is. But remember, reliable statistics cite results of actual research studies. Dr. Suzanne points out that while pregnancies are real and can be counted in these research studies (leading to a pregnancy rate), a particular study's lack of pregnancies may occur as a result of sub-fertility (a very possible reality for some couples) as well as the technical effect of the method used. As such, it is not scientifically correct to subtract any given pregnancy rate from 100% to give an "effectiveness" rate.

For example, if in a study there was one unplanned pregnancy out of 100 participating couples using a particular method (statistically translated as a 1% pregnancy rate), it is not correct to say that the method is 99% effective because some of the 99 couples who did not have a pregnancy would not have had one anyways, using a method or not. Consequently, 99% overvalues the method and is misleading. You can, however, approach the 1% in this way: a couple who follows the rules of the method correctly and consistently has a 99% probability of avoiding pregnancy.

See the difference? THE METHOD is not 99% effective. Rather, A COUPLE has a 99% probability of avoiding pregnancy.

Have we lost you? We admit, effectiveness and stats are not the easiest to grasp. There is more to it than meets the eye. That said, our hope is that you are now adequately equipped to understand the numbers.

Here are the Typical and Perfect Use pregnancy rates2 for some common contraceptives during the first year of use:

Contraceptive Perfect Use Typical Use
Male Condom 3% 15%
"The Pill" (Combined Hormonal Contraceptive) 0.1% 5%
Injectable Depo-Provera (Progestin-only Contraceptive) 0.3% 3%
Intra-uterine Device (IUD) 0.6% (copper) to 0.1% (progestin) 0.8% (copper) to 0.1% (progestin)
Withdrawal (Coitus Interruptus) 4% 27%

Now compare these to Typical and Perfect Use pregnancy rates for the Sympto-Thermal Method in various countries:

Country Perfect Use Typical Use
Belgium3 0% 2%
Canada1 0.5% 5%
France4 1% 6%
Germany5 0.43% 1.79%

Serena has published a document titled Family Planning Methods. In it Dr. Suzanne revised the available research on birth control and comprehensively compares contraceptive methods with NFP methods, not only compiling and explaining their respective use statistics, but also addressing the additional factors we're about to introduce to you. Let us know if you are interested this publication.

Here are a few more factors to consider:

Are there other implications of use? When considering methods of birth control, think of the entire gamut of risks and benefits to you and your spouse. Make an informed choice. Ask yourself:

  • What methods are available?
  • How do they work?
  • Do they affect my health? My spouse’s health? 
  • How much do they cost?
  • Are they convenient?
  • Do they affect future fertility?

When considering methods of birth regulation,what else will impact your well-being and overall satisfaction?

Surely the issue of fertility is not just about avoiding pregnancy! Perhaps there’s more to the equation. Choosing your birth control method is a big decision, a decision that affects your marriage and family, so consider these questions as well:

  • Who bears the responsibility for its use?
  • What is the impact of this method on intimacy in my relationship?
  • What other values are involved in its use?
  • When we’re ready to start a family, will this method help us achieve pregnancy?
  • Will this method positively impact our well-being and our overall degree of satisfaction?

For some answers to these questions, please talk to one of our team members.  

So, what are you to make of all this? Really, there is a lot more involved with birth control than just achieving or avoiding pregnancy. We encourage you to take the time as husband and wife to talk through everything we've shared on effectiveness and satisfaction. Your marriage is worth the time and effort. It's an opportunity for you to draw closer in authentic intimacy.


1.) RICE FJ, LANCTOT CA, GARCIA-DEVESA C. Effectiveness of the Sympto-thermal Method of Natural Family Planning: an International Study. Int. J. Fertil., 26 :222-231, 1981.

2.) TRUSSELL J. The Essentials of Contraception : Efficacy, Safety, and Personal Considerations. Chapter 9 in Contraceptive Technology by HATCHER J, TRUSSELL J et al. Ardent Media, New York, 2004, p. 226.

3.) De LEIAZOLA. Première phase d’une étude prospective d’efficacité du planning familial naturel réalisée en Belgique francophone. J. Gynecol. Obstet. Biol. Reprod., 23 :359-364. 1994

4.) ÉCOCHARD R, PINGUET F, ÉCOCHARD I, DE GOUVELLO R, GUY M, GUY F. Analyse des échecs de la planification familiale naturelle. Contracept. Fertil. Sex. 2, 4 : 291-296.1998.

5.) FRANK-HERRMANN P, HEIL J, GNOTH C, TOLEDO E, BAUR S, PYPER C, JENETZKY E,.STOWITZKI T, FREUNDL G. The effectiveness of a fertility awareness based method to avoid pregnancy in relation to a couple’s sexual behaviour during the fertile time: a prospective longitudinal study. Hum. Reprod, 22, 5 : 1310-1319, 2007.