Monday, November 25, 2013
Article Review: NFP Effectivness to Avoid Pregnancy
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. (2007) 22 (5): 1310-1319. doi: 10.1093/humrep/dem003
Link to free access of article:
Summary (Excerpted from abstract with some modifications)
A study was conducted in Germany with a cohort of 900 women who charted data from 17,638 menstrual cycles using a version of the sympto-thermal method to avoid pregnancy. The symptom-thermal method uses a daily temperature readings, cervical discharge, and optional cervix checks. The results showed 99.4% effectiveness when used “perfectly” (no unprotected sex during the fertile window) and showed 98.2% effectiveness when used “imperfectly” (some sexual relations took place during the fertile period.)
Some Background Information
Warning, biology primer, please skip this if you already know basic human sexual biology: Men are, generally speaking, always fertile from the time they hit puberty, although fertility does decline with age. Women however, are infertile most of the time, with a limited window during which conception takes place. Obviously, for conception to take place, the egg (ovum) needs to be released from the ovary (ovulation), and usually this only happens once a cycle. The egg usually only lives for about 12 hours, and then dies if it is not fertilized. So technically speaking, the fertility window is a matter of hours, not days. However, sperm can live for days in the woman’s reproductive tract! Say sexual intercourse occurs two days before ovulation, the sperm is actually nourished and aided by the woman’s mucus in this time to survive and reach the egg. Thus although 48 hours passed between intercourse and ovulation, a woman may well become pregnant. In fact the most fertile time in a woman’s cycle is the few days preceding ovulation, and the chance of pregnancy rapidly declines once ovulation occurs. Thus it is not simply enough to find out when a woman ovulations, but to plan for, or avoid, pregnancy, a couple should ideally be able to forecast and predict about when ovulation will occur. However, the old-school biology textbook notion of a 28 day cycle with ovulation on day 14, is far from the reality of most women. Thus simply counting days after the commencement of a new cycle is ineffective at planning and avoiding pregnancies. (This is the old rhythm method that is rightfully discredited.) /biology primer
The symptom-thermal method (STM) is based on two primary signs of fertility in a woman: basal body temperature and mucus discharge. For most women there is a spike in temperature on the day of ovulation, and the body temperature will remain raised until the end of the cycle. There will also be an increase in mucus in the days approaching ovulation, typically with the maximum discharge associated with the day of ovulation. (Of course this is ascertained only after the mucus has decreased again.) The reality of this method is slightly more complicated, and can involve also cervical checks and other changes a woman may notice.
Please do not use this summary an effective way to learn STM! In fact one of the keys to success in this study, the authors claimed, was the excellent quality of the teachers and distributed materials that were used in training women and couples in STM. Usually women and couples are taught this method together in a series of classes with an instructor. In the case of this research the instructors were the only ones to know the identity of the participants of the study, and had to form a relationship of trust with participants in order to facilitate honesty and consistency in report back data of a very personal nature, including details of sexual intimacy.
Key Points & Highlights
I am going to use this section to point out what was most interesting or relevant to me. I will not be summarizing the full methods of the research. If you want to dig that deep, I encourage you to refer to the original article using the above link.
First of all, when I read this article I was fairly new to NFP and what was meant by the symptom-thermal method (STM). What constitutes STM can vary by region and teacher as well. The method used in this study is nicely summed up by the following graphic:
I am finding that the main way different NFP methods differ, is in how one identifies the “fertile” time. The median length of the fertile time by the above calculations was 13 days a cycle. With all women in the study having an average cycle length between 22 and 35 days, 13 days may seem like a long time to abstinent. This is a legitimate criticism of the method. In fact, as I will demonstrate in my discussion of another paper, 13 fertile days is very conservative window. By that I mean that the probability of getting pregnant outside that window is in fact extremely low (0.4%), and some couples may choose to engage in some intelligent risk-taking by having intercourse on the “edges” of this fertile window.
In fact that is precisely what some couples in this study did. Those couples engaging in unprotected sex during the “fertile” time had pregnancy rates of around 7.5%. One could make the point that this is a nearly 19 fold increase, however one would expect the pregnancy rate to in fact be much higher if couples are engaging in sexual intercourse when a woman is “fertile.” 7.5% is shockingly low, and the authors of the paper attribute it to the fact that couples, although failing to adhere to the advice of abstaining from unprotected sex during the fertile window, are still using their knowledge of fertility awareness to avoid the few most fertile days of a woman’s cycle.
Interestingly, there was no significant difference in unintended pregnancies in those couples choosing to use barrier methods of contraception during the “fertile” window and those choosing abstinence.
Conclusions and Contentions
The high success rate of avoiding unintended pregnancies is remarkable. The pregnancy rate was 0.4 (per 100 women) for those adhering to the guidelines, and 1.8 (per 100 women) overall, including those using the method imperfectly over the course of a 13 cycle (approximately one year) period.
How does this compare to other forms of birth control? Well, I did what most teenage girls across America would do (although I am no longer a teenager) and went to PlannedParenthood.org for some reliable information on birth control. When I clicked a link labeled “Effectiveness of birth control” I was sent to the following graphic:
Oh no! According to Planned Parenthood, it looks like “Fertility-Awareness Based Methods” like STM are only 75% effect at birth control! That is no good! However, when you click the link for “Fertility-Awareness Based Methods” it lists out a variety of methods, including STM, which it does state as having a less than 1% (0.4%) failure rate. So why do they lump it at the bottom with spermicide? Maybe because they include it with the “Calendar” method which is simply based on counting days, and other less efficient methods. Planned Parenthood is also quick to point out that “If you have unprotected sex on a day that you may be fertile, emergency contraception is a good option.” I’ll try to bite my tongue here, but let me just say that Planned Parenthood, in spite of its non-profit status, is a money-making institution, and so there is perhaps a vested interest in listing FAB methods at the bottom of the birth-control totem pole.
Planned Parenthood states that if you always use a condom, it will result in an average of 2 pregnancies per 100 women (proper use), and if not always used properly and consistently, will result in 18 pregnancies per 100 women. Compare those stats to the 0.4% and 1.8% of STM.
What about the pill? Again, Planned Parenthood states that 1 out of 100 women who always take the pill every day for an entire year, will become pregnant, and for women who don’t always take the pill everyday as they are supposed to, the number is 9 out of 100. Again, STM wins.
And the best part is, STM is of virtually no cost to the woman. There is an upfront investment in taking the time to learn the material, and ideally attend a few classes with a trained professional. It does not suppress a woman’s fertility, as synthetic hormones do, and has no side effects, so the very month a woman and her partner change their mind about their desires to conceive, they can use the same knowledge that helped them to avoid pregnancy, to now achieve it. There are no side-effects, and there is nothing you have to buy and keep handy in order to have sex. (Actually, it does require investing in a thermometer, but these are relatively inexpensive, less than the cost of condoms over a year! Plus you can use the thermometer when you are feeling sick and wondering if you have fever!)
What about the fact that you have a possibly long (13 day median) period of time in which you must abstain from (at least unprotected) intercourse? This is a valid point, and one I am still struggling with. It should be noted that the drop out rate from dissatisfaction was 9.2 per 100 women per 13 cycles (year). This rate is low, and not all women left for dissatisfaction with the method. Some left because of a “desire to achieve a pregnancy (8%); separation from partner (2%); medical reasons (4%) and most frequently (22%) because they wished to discontinue participating in the study, although they wished to continue to use the STM.” One critique I have is that the above percentages only add up to 36% and I would like to see a data table of the other reasons women gave for exiting the study.
I am still wondering if the 13 day median of a fertility is too conservative. No woman is fertile for 13 days, it is impossible! The egg only lives for 12 hours, and sperm can realistically live at longest for 5 days in a woman, and this is a very small percentage that can live that long. So why the 13 day window? Because of the nature of forecasting a woman’s day of ovulation. There is some natural variability in cycle length, and outside factors and also impact a woman’s cycle, such as illness. So the large window is to minimize the risk of pregnancy due to this variability. However, my guess is, and I haven’t been tracking my own signs long enough to know, that for some women they can learn their own biomarkers well enough, and may have stable enough cycles, to reasonably reduce that window further. The researchers had to define a wide window of fertility to accommodate the diversity of cycle types, and variability for even one woman. But my feeling is that not all women need to be as conservative, and after learning the method and their own bodies, may be able to make some well-informed calculated risks, narrowing the abstinence/fertility window. I am certainly not recommending this and don’t mean to undermine the sound counseling of trained professional NFP teachers. These are simply my own conjectures.
The next paper I comment on will discuss be a large demographic study on the daily fertility rates of women to examine this question of the fertility window more deeply.