Let's dive right in!
Probability relative to Temperature Rise*
9 days before temperature rise - 0.3%
8 days before temperature rise - 1.4%
7 days before temperature rise - 6.8%
6 days before temperature rise - 6.8%
5 days before temperature rise - 17.6%
4 days before temperature rise - 23.7%
3 days before temperature rise - 25.5%
2 days before temperature rise - 21.2%
1 day before temperature rise - 10.3%
1st day of high temperature - 0.8%
2nd day of high temperature - 3.5%
3rd day of high temperature 0.0%
Probability relative to Mucus Peak Day
9 days before peak day - 0%
8 days before peak day - 0.3%
7 days before peak day - 0%
6 days before peak day - 4.5%
5 days before peak day - 7.8%
4 days before peak day - 18.1%
3 days before peak day - 11.4%
2 days before peak day - 20.3%
1 day before peak day - 17.7%
Peak day - 13.5%
1st day after peak day - 6.7%
2nd day after peak day - 2.0%
3rd day after peak day - 0.5%
4th day after peak day - 0.0%
Probability relative to Day of Ovulation
6 days before ovulation - 0%
5 days before ovulation - 7%
4 days before ovulation - 11%
3 days before ovulation - 9%
2 days before ovulation - 18%
1 day before ovulation - 21%
Day of ovulation - 22%
1st day after ovulation - 0%
Stats taken from: Daily Fecundability, Demographic Research, 2000 (800 women, 7017 cycles), and Timing of Intercourse in Relation to Ovulation, New England Journal of Medicine, 1995 (221 women, 625 cycles.)
* The probabilities relative to temperature rise were based on traditional BBT charting and haven't been evaluated using overnight sleep temperatures via wearables.
Now let's really get into the nitty gritty!
You may be wondering where a monitor peak might fit. According to Clearblue Research, for the ClearBlue Fertility Monitor, most - approximately 97% - of ovulations occur over the two days of peak (and of those, the majority fall on the second peak) and the high following. The majority of ovulations (approximately 91%) coincide with the first or second day of monitor peak, with a significant minority (approximately 6%) occurring on the day of high following the second monitor peak. The remaining 3% happen later than that. So when estimating an approximate probability of conception based on Clearblue monitor readings, the easiest approach is to provide a range assuming ovulation likely occurred over the PPH pattern of results.
The probability of conception based on mucus peak day could be different depending on what method you use, as they can define peak day differently. So you could also provide a range based on likelihood relative to ovulation, tying that to where ovulation likely falls according to mucus peak:
According to research from the Billings Ovulation Method, ovulation occurs on mucus peak day or the two days following.
According to Sympto-Thermal Method research, ovulation can occur up to 2 days before to 2 days after mucus peak day.
According to Creighton Model research, ovulation can occur up to 3 days before to 3 days after mucus peak day, but most often occurs up to 2 days before to 2 days after mucus peak day.
Generally, the closer you are to peak/ovulation, the higher the chances of conceiving. That pattern isn’t perfect in these lists. These statistics have come from specific study samples. For example, look at the probabilities relative to mucus peak day. You'll notice that the in the above list the stat for conceiving from sex 7 days prior to peak day (mucus) is 0%, but for 8 days prior to peak day (mucus) it is not 0%, but 0.3%. Is there anything special about 8 days prior to mucus peak that makes it potentially more fertile than 7 days? Very unlikely. It’s logically sound to conclude that it is indeed possible to conceive from intercourse 7 days prior to mucus peak. What it means is in that limited group of women who were studied, nobody happened to conceive from intercourse 7 or 9 days prior to mucus peak but one person did from intercourse 8 days prior to mucus peak. Really, what you can say is the chance of conceiving between 7 days prior to mucus peak is somewhere within the probabilities for 6 and 8 days prior to peak, so somewhere between 0.3% and 4.5%. The patterns might be a bit different and even out if we were able to study many, many more women. Wait... a woman conceived from intercourse a whopping 8 days prior to mucus peak day? Does this mean this was an occasion of "supersperm" with 8 day sperm survival? Not necessarily. Remember that in some charting systems/research studies ovulation can occur before mucus peak day. That woman may have ovulated 2 days prior to mucus peak day, which would give a 6 day sperm survival.
There are also some other studies that could be used for data, which come up with differing stats. Contraception and fertility studies are generally comprised of women who are between about 18-43/45yo, in regular cycles (typically between 21-42 days long), and with no known fertility issues or reproductive health issues, like PCOS or sub-fertility. A good study will start at around 200 participants. There are other ways to determine the likelihood of pregnancy based on the day intercourse occurred prior to ovulation. Since I recently mentioned sperm survival, see: http://www.ncbi.nlm.nih.gov/pubmed/9288325 This paper finds a 1% probability of sperm surviving more than 6.8 days.
Here are some other approaches:
As you can see, unless you're a medical research stats nerd, it starts getting too complex to provide a holistic overview, when most people are just wondering what their ballpark probabilities are. I created this post just to provide a general idea or a very rough guide. If you have intercourse two days before mucus peak day and three days before temperature rise, you could say your statistical chance of pregnancy is something between 17-26%, roughly. Your actual chances of conception in real terms depend very much on your combined fertility as well as day timing. Some couples have better combined fertility than others, and will conceive more quickly or easily, and may be more likely to have longer sperm survival due to both male and female fertility factors, while other couples may take longer, find conceiving harder, and need to time intercourse optimally for success.
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