Basal Body Temperature 101

Probably the most annoying of all the fertility charting methods, just because it's an absolute pain in the backside to do. I had my thermometer tucked under my pillow to use every morning, at 5am, before I got up, and it always took me a good ten minutes to half an hour to get back to sleep. I was then tired for the rest of the morning. However, I can't deny that it was incredibly useful in my charting journey as I could pinpoint when ovulation had occurred with precision.

How does it work?

The general rule is that your basal body temperature has two, maybe three, phases. Before ovulation, post-ovulation, and then, maybe, pregnancy. Before ovulation your temperatures will be lower than the other phases. After implantation it could rise again. Or it could just rise again for no reason. That's the fun of TTC – it could be something, it could be nothing.

Your temperature will rise after ovulation. This is caused by the hormone progesterone (produced by the corpus luteum) – progesterone does a lot of things which we will come to later. So this rise is supposed to be able to confirm ovulation quite definitively.

While not the best example, this chart shows the three phases of what your chart could go through. The start, lower, then the red crosshairs pinpoint the day of ovulation, and then the rise. You can use only basal body temperature, but as you can see from this chart I have used opks, cervical fluid and temperatures. This chart was made using the Fertility Friend app.

How do I do it?

In order to accurately chart your basal body temperature you will need something to chart it on, and a thermometer. Some people choose to chart on paper but, wow, paper is so archaic, right? Apps are the way forward in this increasingly modern and technology dependent world, so what's the best app for charting your basal body temperature?

Personally, I find Fertility Friend to be the best app – it's free, and also has a VIP paid option (which I found was useful, and I did end up paying for twice). I know that Ovia also allows you to input your basal body temperature, and so does the Apple Health app. However, Fertility Friend allows you to see all of the temperatures in one go and so a pattern is much easier to see.

To take your temperature you're going to have to keep your thermometer by your bed, either under your pillow or on a nightstand. You are supposed to take it at the same time (within half an hour) every morning, before you're out of bed, before you move, before you speak, before you do anything.

You can take your temperature orally or vaginally. Orally, for me, was more convenient, and it seemed to be more hygienic, but vaginally is more consistent if you end up breathing through your mouth in your sleep.

Is it for me?

Yes! BBT charting is a really great way to get to know your body and your cycles. I have found that after a few months of tracking, if you have a regular cycle, you can slack a little bit and go back to only using opks, or even not using anything at all. If you don't have a regular cycle it can be, again, a great way to get to know your body and your cycles, and to make sure you've caught that little egg – it is especially helpful if you do not have a partner and will be using a donor.