I have a nice long post sitting around about Fertility Awareness/NFP and how it requires a lot of work/abstinence. But over the past few years I have become aware of the fact that others have a very different view of this than I do. It has also been 3-5 years since I was reading NFP studies and I am beginning to realize that I don’t remember as much as I’d like to think I do. So, this is a call for help.
In your experience, how many days in a typical cycle would you identify as fertile for the purpose of avoiding pregnancy? And by “identify as fertile” I mean abstain from sex on the day in question, not which days you’d guess were actually fertile once you were looking back on the completed chart after the cycle was over.
The second request is for you to provide studies that show how effective your method is for avoiding conception.
For instance, CCL cites a study that indicates a 99.6% method effectiveness for avoiding pregnancy. And when you look at the actual study you see that there was an average of 13 days per cycle that were identified as fertile and required abstinence.
Based on my understanding of NFP, there are 6 days per cycle that could really be fertile (sperm life + egg life), and an additional 3 days (to account for the possibility of double ovulation and to confirm that it was indeed ovulation– not merely a disturbance in temperature or cervical fluid building up to ovulation but then stopping without ovulation). That means that unless one is either counting on lower fertility (for instance, assuming that a woman will only have a few days of fertile cervical fluid so the sperm could only survive 2-3 days) or else taking chances with not really confirming ovulation, the minimum number of days a (blessedly healthy) woman can expect to identify as fertile is 9.
I recently re-read through the instruction manual for the method that Josh and I learned while engaged (the Cross-Check Method: think STM flirts with Marquette) with the goal of figuring out the least amount of abstinence possible for a healthy woman who was seriously determined to avoid pregnancy. After playing around with the various rules, the shortest that I could come up with was 10 days. A quick review of our practice charts (theoretical, not my body’s data) revealed that the shortest was, in fact, 10 days.
And I am just focusing in on the shortest possible length of time. I know quite well that for many women there will be many months where they must abstain for much longer if they are truly serious about avoiding conception.
So, help me out here. Does your experience or training indicate something else? Please, please, please do direct me to studies. At this point I am thinking that a week of abstinence may get many women a 90-95% method effectiveness rate for avoiding pregnancy, but I just can’t see how it would take less than 9 days to get to 99%.
What am I missing? I don’t want to be ignorant and say silly things in future posts.















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