Ovulation and Temperature: The Hidden Key to Tracking Fertility

Body temperature and the menstrual cycle

When we think about our body temperature changing we usually think about being ill and having a fever or the chills. However, even when we’re healthy, women’s bodies have a natural temperature fluctuation that’s actually linked to the menstrual cycle. 

There’s an identifying point in a cycle when body temperature changes. This happens in the second half of the menstrual cycle, when there is a noticeable rise in temperature right after ovulation happens. Take a look on the graph below:

Why does temperature rise after ovulation?

So now we know exactly when temperature changes in the menstrual cycle, but why is there a rise in temperature after ovulation? The reason for this is hormonal. Levels of the hormone, progesterone, rise after an egg cell is released. Progesterone raises body temperature, so you’re likely to get a higher temperature reading in the latter half of your cycle. 

If no egg is fertilized, then progesterone levels drop again (as does your body temperature). This cues the uterus lining to shed, leading to your period and the start of a new cycle. If you don’t find a shift in temperature, it’s possible you’ve experienced an anovulatory cycle – this is when ovulation doesn’t happen. It’s fairly common, but unless you’re tracking your temperature you might not notice it happening. 

Tracking fertility with temperature

Once you’re able to detect ovulation, you’re able to detect your fertility as this means you can pinpoint the fertile window – that’s right, you can’t get pregnant every day of your cycle. There are only a small numbers of days in any cycle when it’s possible to get pregnant. Identifying these gives you the power to plan or prevent pregnancy with a hormone-free method.

However, to measure this small, yet significant shift you need to measure BBT (basal body temperature), which requires a thermometer showing two decimal places. Basal body temperature is the body’s lowest resting temperature which can be measured in the morning as soon as you wake up. 

Regular measuring can help you find ovulation day. However, it’s worth remembering that for both planning and preventing pregnancy, the most fertile days happen in the lead up to ovulation, this is because of the length of sperm survival. 

This is where ovulation prediction comes in. Natural Cycles uses an algorithm which learns your unique cycle and can predict your fertile window ahead of time, so you know when you are most fertile and can plan a pregnancy or use protection on those days to avoid getting pregnant.

What can affect tracking fertility with a temperature method?

There are a number of factors that can influence our bodies and are worth keeping in mind if you are considering tracking fertility with a temperature method. These include:

• Illness/taking medication
• Being hungover
• Jet lag/travel
• Sleeping significantly more or less than usual
• Some thyroid conditions

However, we like a glass of wine from time to time, and no one can help getting sick – so how can we factor in those changes to our routine? Unlike traditional temperature methods, the Natural Cycles app has a built-in deviating temperature feature which lets you log any changes which might affect your BBT. If you have a thyroid condition, PCOS or another condition which can affect your body temperature, Natural Cycles will still work for you, it might just take a little longer to learn your cycle.

So now you know the link between ovulation and temperature and its role in fertility tracking,  there’s lot’s more to learn about your body and your unique cycle. At Natural Cycles we’re committed to closing the knowledge gap when it comes to reproductive health.