Disclaimer: As with any time I write about the specifics of fertility awareness, I’ve gotta remind you that you MUST take a class or AT LEAST read a full book on the sympto-thermal method of fertility awareness to practice it properly. Reading blog posts and downloading an app does not cut it, kapish?
It’s a Q&A day! I got this question and I actually think it will make a really nice beginning of a series: Why do the rules exist?
Essentially, when you are using the sympto-thermal method of fertility awareness you are doing a few things:
- Checking your fertility signs.
- Charting your fertility signs.
- Applying “rules” to those fertility signs so that you know when you are inside and outside of the fertile phase of your cycle.
Knowing why the rules exist is very important because it helps you understand what rules you should never ever break if you are very strictly trying to avoid pregnancy, and what you might not care about if you are a little more on the “umm… I kinda don’t want to get pregnant, but at the same time I don’t really mind if I do get pregnant”- side of the trying to avoid scale. It also helps you understand how your hormones and cycle work better, making you a better user of the method.
That being said, let’s get on with today’s post!
I am recently married, and have been charting my cycles and symptoms for about four months now. I feel that I was able to get a good grasp on how FAM works before the wedding, but there is one rule that I just don’t understand- the peak day +3 (or +4) rule.
I am confused because from my understanding, it is common for your temperature shift to occur the day after your peak day, or sometimes two days after. Isn’t the temperature shift an indicator that ovulation has already occurred, and that the egg has come and gone, due to the release of progesterone from the corpus luteum? So why is the beginning of the infertile phase not marked by the temperature shift instead? Why is is necessary to wait extra days to be considered infertile?
If you could help me with this, I would appreciate it very very much. Thank you.
I want to break this into two sections, since one is going to be a little more general about peak + 3 and the other is going to specifically address the question.
What is peak + 3 and why is it a thing?
To identify peak + 3, your first have to identify your peak day, which also means you need to identify your cervical fluid and be able to tell the difference between peak type fluid and non-peak fluid. Once you have that down, you can determine your peak day, which just means the last day of peak-type cervical fluid.
Your last day the last day of peak-type cervical fluid is closely related to when you actually ovulated. You can not pinpoint the exact day of ovulation with your fertility signs alone, however, which is where part of the rules come in.
In this case, what we know is that peak day is correlated with ovulation with an accuracy of plus or minus 3 days. That means that your ovulation can happen any time from 3 days before peak day to 3 days after peak day. The percentages look something like this:
- -3: 7% chance of ovulation
- -2: 7% chance of ovulation
- -1: 14% chance of ovulation
- 0 (peak day): 37% chance of ovulation
- +1: 21% chance of ovulation
- +2: 14% chance of ovulation
The third day after peak is given for a potential second ovulation and the life of that egg, which can be up to 24 hours. These numbers are found by doing studies in which women check their cervical fluid and get daily ultrasounds to confirm exactly when ovulation happened.
This, my friend, is the reason we count those days. If you want to be CERTAIN you have both ovulated and the egg has died, you want to have 3 days post-peak to confirm that.
But how does temperature shift play in to this rule?
The question above goes beyond just why the peak day rule exists and into
- Why peak and temperature rules need to be cross checked, and
- Why you aren’t infertile as soon as your temperature rises.
The answer to the first is that if you want the highest efficacy available, you want to use two signs in order to confirm that you have ovulated. If you only use your temperature, you could get thrown off by your batteries dying, mild illness, poor sleep, or some other outside factor making your temperatures momentarily elevated. If you work on only cervical fluid, you could have your body attempt to ovulate, fail, return to lower hormonal levels, and see a cervical fluid dry up because of that. That could last a few days before seeing a build up of cervical fluid again. With a temperature rise to cross check, you know that the dry up was indeed due to ovulation and wasn’t a failed attempt.
Regarding the temperature rise, it will certainly be explored further in this series, but for now here is what is good to know:
Temperature can rise the day before or day of ovulation, as we have seen in even small studies. Why this is the case isn’t fully known. It could just be one of many factors that could make a temperature jump happening just before ovulation, or it could be due to your actual hormonal activity. Luetinization of the follicle is what creates the corpus luteum, which is what starts progesterone production. While luetinization of the follicle often does start before ovulation happens, it’s not perfectly clear whether it’s enough to raise your progesterone levels significantly enough to see a temperature rise.
Because of the rise that can happen pre-ovulation, it’s important to give 1 day for ovulation to happen, 1 day for that egg to die, and another day for a potential second ovulation and the life of that egg.
Together these two rules give you nearly infallible insurance that you have actually ovulated and that the egg is already dead. These rules are not meant to tell you exactly when you ovulated and give you the very most days of infertile time, they are designed to work with what we actually know about our fertility signs and how they relate to when we can get pregnant and are rather conservative because of the variation that can be seen between women.