Basal Body Temperature: How to Recognize Your Fertile Days

You wish to have a baby or you want to use natural contraception? By measuring your basal body temperature, you can find out your current fertility status without the need for ovulation tests.

In your cycle, there are many different symptoms that indicate ovulation and give clues about the hormonal changes in your body. In addition to the cervical mucus and cervix, one of the most meaningful methods of measuring basal body temperature, also known as the temperature method.

Basal body temperature – What is that exactly?

The basal body temperature is your body temperature shortly after waking up – i.e. exactly the temperature you take while still lying in bed. This is important because our body temperature changes constantly throughout the day and is subject to a 24-hour rhythm – it is lowest in the early morning and highest in the late afternoon.

However, in order to be able to determine ovulation accurately, you need comparable values that are as unaltered as possible. For example, if you go to the toilet first or make yourself a cup of coffee, your body has already warmed up.

Therefore: Before you do anything else in the morning – measure your temperature!

Basal body temperature method – How does it work?

1. Clinical thermometer on the bedside table: From today on, this is your most important aid. So that you can take your basal body temperature without falsifying it, place your thermometer within reach, for example on your bedside table.
2. Take a temperature: Taking temperature is your first action of the day. Start at the beginning of your cycle. So on the first or second day of your period with taking your temperature. Your basal body temperature curve is only complete at the end of your cycle.
3. Write down your values carefully: write down the temperature you took in bed in the morning. You can either make a chart for yourself or use a cycle chart (for example, from the Internet). Of course, your data is also in good hands in an app or a cycle computer.
4. Stay on the ball: To get a meaningful basal body temperature curve, you now follow this procedure every morning. Don’t worry, it may be unfamiliar at the beginning, but you get used to it quickly.

Advantages of the temperature method

• natural contraception without interference in the body’s processes by, for example, hormones
• contrary to many opinions, the method has a very good contraceptive safety index when used correctly
• you get to know your body and expand your knowledge about the processes in the female body
• the method is almost free of charge

Measure correctly – You should definitely pay attention to this

The accuracy of the method depends largely on the correct measurement of the basal body temperature. These factors essentially determine the result:

• Time: Measurements are taken immediately after waking up, lying in bed, at best always at the same time
• Duration: The measurement duration has a decisive influence on the value. A measurement duration of three minutes is therefore considered to be reliable.
• Thermometer: Most digital thermometers beep much earlier, you should use an analog clinical thermometer or a model especially suited for the basal body temperature method
• Measurement locations: under the tongue (mouth closed!), vaginally or rectally. Under no circumstances under the armpits! When you have decided on a location, stick to it.

Interpreting the temperature curve correctly

Your temperature level has a typical course during a trouble-free cycle, which you can understand by your values. In the first half of the cycle the basal body temperature is slightly lower, which is why this phase is also called depression.

1 to 2 days before the temperature rises, you will often notice a slight drop in temperature. This low temperature is just before ovulation. Your temperature then remains elevated until the next menstruation, which is why this second phase is also called high. Shortly before your period the temperature drops again.

When is ovulation?

• if, a stair-like or steep rise in temperature follows within 48 hours or less
• if, for three consecutive days, your waking temperatures are at least 0.2°C higher than during the previous six days

Although the method does not allow the ovulation to be predicted exactly, the probability of ovulation can be limited based on experience from previous cycles. The more cycles observed, the better.

Why does the basal body temperature change at all?

From the middle of the cycle, i.e. after ovulation, the sex hormone progestin is produced. This in turn influences the body’s thermoregulation centre and causes the body temperature to rise. Therefore, the temperature level in the first half of the cycle is lower than in the second half.

Progestins, in turn, are only produced when ovulation has actually taken place, so the rise in temperature is a fairly reliable indicator of this. Overall, the temperature remains at this level for about 13 to 14 days, only to fall again shortly before the period. If the temperature level remains at the same low level throughout the cycle, ovulation has probably not occurred.

Basal body temperature and desire to have children

If you are currently in the process of family planning, this method can help you to achieve your dream of having children more quickly. For example, the basal body temperature method can help you identify your key fertility window – the best time to have sex with your partner to get pregnant.

If you are planning a pregnancy, you can narrow down your infertile and fertile days even more precisely by using NFP as a symptothermal method and observing either your cervix or cervical mucus in addition to the basal body temperature.

Elevated basal body temperature as a sign of pregnancy

If you are already in the middle of family planning and are waiting impatiently to see if it has worked out, the temperature method can also provide the first indications of a pregnancy. A raised basal body temperature is one of the first signs of pregnancy. Your wish for a child could therefore soon come true. In a healthy woman, the basal body temperature drops just before the period. If your temperature doesn’t drop but remains constantly high (like at ovulation), pregnancy is very likely.

Prevention with the temperature method

If you want to use natural contraception and avoid taking hormones, such as the pill or the IUS, this is a recommended method of contraception. The easiest way to use the basal body temperature method is to use a cycle computer, which does the fertility analysis for you and tells you when it is better to use a different method of contraception or not to have intercourse. Even safer than the temperature method is NFP or the symptothermal method, which has a similarly high Pearl Index as the pill.

These interference factors can influence the temperature:

• Changes of location and travel can falsify the temperature.
• In case of feverish illnesses and light colds, measuring can be suspended.
• Medication, such as sleeping pills, psychotropic drugs and hormone-containing preparations change the body temperature.
• After large consumption of alcohol the body temperature is changed.
• Sleep of less than five hours or even bad sleep, as well as a sleeping environment that is too warm can influence the temperature

Of course, it takes some time at first before you can interpret your basal body temperature curve. But after two to three months you will develop a feeling for it and recognize a pattern. So you will know in good time when your fertile days are about to begin.