The woman’s body is really a remarkable thing. Cycle after cycle, the uterus does its job and releases another egg, expecting it to be fertilized. Today, since we have such great knowledge through medical research on what’s going on in the uterus, we can use it to our advantage to either prevent or plan a pregnancy. The time frame when a woman is fertile only occurs once per cycle and is called the fertile window.
The fertile window includes the 5 days prior to ovulation and the day of ovulation.
The 5 days period prior to ovulation is determined from the longest time sperm can survive in the uteral environment. Note, however, that most sperm have a lifetime significantly less than 5 days – more like 2 or 3 days, but to completely exclude a possibility of pregnancy one must take the longest living sperm into account. For sperm to survive any significant time at all, the uterus must contain the fertile type of cervical mucus, which helps the sperm to live longer as well as to be able to travel up the uterus and fallopian tubes. Without the presence of fertile cervical mucus sperm typically only survive about 4 hours.
The fertile cervical mucus is triggered by a rise in estrogen prior to ovulation. The amount of fertile cervical mucus does not only vary from woman to woman, but also on the age of the woman. The older you get, the fewer days you produce cervical mucus and hence the narrower your fertile window becomes.
Once released through ovulation, the egg can maximally survive up to 36h, but typically only 12-24h. Studies have shown that the quality of the egg deteriorates very quickly; causing the probability of conception to decrease rapidly every hour once the egg has been released. For optimal chances of conception, sperm should thus already be present in the fallopian tube once the egg is released. Therefore, the most fertile day of the woman’s cycle is rather the day prior to ovulation than the day of ovulation itself.
To prevent pregnancy through detecting ovulation and predicting the fertile window, one must assume the longest living sperm and egg. This sums up to 6 days in the cycle. What’s more tricky is to accurately calculate the uncertainty of the ovulation day for a woman. That is, when do we think she will ovulate and what’s the earliest possibility of ovulation to occur. Luckily this is what NaturalCycles‘ algorithm does for you. When you start measuring your temperature, NaturalCycles will be very cautious as it does not know around what time you usually ovulate. With more and more data, NaturalCycles is able to better estimate your ovulation day, the variation of your ovulation day and the uncertainty on the estimated variation of your ovulation day. All this is required for a full-proof birth control method using natural family planning. So don’t chart by hand to prevent getting pregnant ladies – it is doomed to end up in an accident. Use the mathematical tools provided for you and you’ll save both time and hassle.
One question about tracking the basal body temperature for natural family planning is when to refrain from measuring. If you are clearly sick and have a fever, NaturalCycles will detect your temperatures as abnormal and automatically exclude them. However, if you are just feeling slightly under the weather, or have been partying the day before, or simply sleeping significantly more or less than usual, your temperature measurement for that morning could be slightly shifted. This is not at all “dangerous” and it will not make you get green days during your fertile window. It could however cause you to get less green days as NaturalCycles provides the same level of safety for all types of temperature fluctuations.
It is therefore better to refrain from measuring for days where you don’t follow your normal rhythm. Especially if you haven’t just started measuring your temperature. NaturalCycles uses all of your data data from the first cycle you enter, when it analyses your new incoming temperatures and therefore, after three cycles or so, statistics become less crucial. Myself, I have now used NaturalCycles for 500 days and I have meanwhile acquired quite some statistics. I therefore only measure on days where everything is according to my normal every day schedule. For example, before this morning (Monday), I did not measure since Wednesday (see chart). Thursday was the Swiss national holiday so there was some drinking involved for both Wednesday and Thursday evening. Then, during the weekend, I slept considerably longer than usually. Since my data are not limited by statistics anymore, and I am not yet close to ovulation, it is fine for me to skip those 4 days in a row. I you have a look at my chart below you see that there is a nice line until today, probably since I skipped the days before where I’d otherwise get elevated temperatures due to sleeping in/alcohol.
I will summarize some useful rules of thumb that you could adopt for optimal temperature tracking:
- For the first 3 cycles, try to measure as often as possible
- For the 5 days before and after expected ovulation, try to measure almost every day
- Outside these two scopes try to at least measure 4 mornings/week, but strictly don’t measure if:
- You get more than 2 hours of more/less sleep than usual
- You wake up more than 3 hours earlier/later than usual
- You drank more than usual the evening before and you feel the alcohol the following morning
- Skip the first morning after having traveled long distance to a different time zone
- You feel ill or have a fever
If you apply these guidelines, you should get nice temperature curves. There will of course always be some fluctuations, which cannot be avoided, but that’s normal and nothing to be concerned about. You should also try to avoid first measuring and then deciding whether to use the temperature value or not. That might bias your chart to look like you want it to, rather than what is actually correct.
When you have to measure the LH hormones with ovulation tests (OPKs), you don’t have to worry about more/less sleep or alcohol.
You should however try to not drink any liquids and not go to the bathroom at least 2 hours before measuring, preferentially more than 4 hours. Best is also to avoid taking the test in the morning. This might sound confusing, as pregnancy tests are best taken when you wake up, but the LH surge often starts in the morning, so if you take your ovulation test then you are more likely to miss your LH peak. Of course, if you don’t find a good time during the day to avoid liquids for a longer time, then the morning is to be preferred.