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Basal Body Temperature vs Ovulation Predictor Kits

21 October 2020

So, when we are trying to conceive, we try to keep everything under control. This is particularly true for our ovulation as we know that it represents the fertile window, i.e. when we need to get romantic with our partners. There are some strategies to help us identify that short period to avoid missing another month. Two options are checking our basal body temperature and tracking the Luteinising hormone (LH), but which is best for us? Let’s have a look!

Basal Body temperature (BBT)

Our basal body temperature is the first temperature measured in the morning when we wake up, before getting up or doing anything else. When we are about to ovulate, our body temperature rises half a degree. The idea is to track your temperature every morning so you can identify your fertile period. You can track it on an old-fashioned piece of paper, or by downloading apps designed for that.

How do I check my BBT?

Checking your BBT should not be difficult, but try to be consistent and measure it first thing in the morning, even before sitting up or talking. It is better to use a digital thermometer, as they are slightly more accurate and easier to read. Keep your records on a paper chart or an app. When you see that your temperature has risen half a degree, that means you have ovulated, especially if that rise is there for the next couple of days. Once you have done this for 3 months, you will understand your body better, and you will be able to identify the pattern and predict your next ovulation cycle.

When should I have sex?

The idea is to have sex before, while or straight after you are ovulating. Your BBT increases one or two days after the ovulation; therefore, you should have sex before you see the increase. That is one of the drawbacks of this method because you get the info after the event, so it is too late. However, if you have predictable cycles, this method may work for you as you can predict your fertile window better. You can be even more accurate by checking other signs, for instance, your cervical mucus which becomes clearer, thinner and more slippery.

What is the difference between BBT and ovulation predictor kits (OPK)?

An ovulation predictor kit measures LH levels, which surge before ovulation. Therefore, OPKs can detect your fertile window in advance, before ovulating. Ideally, we should start having sex before the surge, and when the test becomes positive, we can increase the frequency. Sometimes, LH spikes are very short, so if we are not checking it regularly, we might miss the surge, and this is its main drawback.

What is best, BBT or tracking LH levels?

Both methods can be good if we know how to do them, but both also have pros and cons:

BBT pros:

  • It’s useful to understand better how your body works
  • It’s very cheap! You just need a thermometer and a piece of paper
  • It’s natural and less invasive 
  • It’s eco-friendly – no sticks, so less waste for the environment

BBT cons:

  • It’s retrospective; body temperature rises once you have ovulated
  • It requires dedication! You need to do it first thing in the morning
  • It can take months to understand your cycle
  • It’s not very precise
OPK pros
  • It measures LH which precedes ovulation – therefore it’s prospective
  • They are generally accurate and convenient; you don’t need to fill in a chart every day
  • They are widely available – you can find them in any pharmacy
  • It’s easy to use – similar to a pregnancy test
OPK cons
  • They can be inconsistent, especially in women with irregular periods
  • You can miss the surge – the LH peak can be very quick, so if we don’t check often, we can miss the peak and think we did not ovulate
  • LH tests, as with any tracking equipment or external support,  does require an ongoing purchase.
  • They do not always work if you are using fertility drugs –ask your doctor about it if you are in any treatment.

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