Basal Body Temperature Basics

What about the Drawbacks?

While there are no serious drawbacks to using BBT—there aren't any side effects or anything like that—there are a few reasons why this method may not be right for you. For instance, it takes some patience. What you are really looking for is patterns, which will only emerge after regular tracking for more than a month. You have to be consistent too, taking your temperature every morning.

Basal body temperature can be affected by external factors, such as taking certain medications or your activity level, so if you don't take note of those factors your results may seem confusing.

"The main downfall with tracking basal body temperature and ovulation is that with this method, you don't actually know you're ovulating until the tracked temperature goes up," says Beltsos, which means that your fertile window has already passed. This can be frustrating until you have charted your temperature for several months and can read and predict the patterns. In other words, you won't get an indication as to when you would conceive the first month you chart your BBT.

How Successful Is BBT in Predicting Fertility?

"BBT is very good at showing that ovulation has occurred," says Beltsos. But it's not good at helping you know ahead of time when that might occur. If you have other fertility issues, such as blocked fallopian tubes or endometriosis, tracking your BBT will not necessarily expose them.

Charting Your BBT: A Step-by-Step Guide

In order to begin charting your basal body temperature, you need two things: a good digital BBT thermometer and a place to chart. (Most thermometers come with a chart.) Now, you will want to keep these materials right next to your bed so you can take your temperature immediately after you wake up each morning. "It is important that the temperature is measured while [your] head is still on the pillow," says Beltsos. Then write down the temperature on the chart.

The basal thermometer is different from the ordinary household thermometer used for detecting fever. It makes smaller changes easier to detect. We're not talking huge swings of temperature here, but fractions of a degree.