By Published On: January 18th, 2024Last Updated: January 18th, 2024
An image composed of three photos. From left to right, the first one shows cervical mucus stretching between two fingers. The second one shows a digital thermometer and a temperature reading in it. The third one shows an LH test strip with two red stripes, making it a positive test result

Your fertility biomarkers are the language your cycle uses to communicate with you!

Your body gives you clear physical signals to let you know when your fertile window is open (you’re only fertile for about 6 days every cycle). These signs are called fertility biomarkers, and they change during your cycle, depending on whether or not you are fertile at the time.

And they also give you important clues about your hormonal health! They can tell you if your hormones are balanced, or if there’s an underlying issue.

The main fertility biomarkers are:

  • Cervical mucus,
  • LH hormone surge,
  • Basal body temperature,
  • Period and other bleeding patterns,
  • Among others.

Learning to identify, chart and interpret your fertility biomarkers is incredibly useful! Among other things it can help you:

  • Identify the ovulatory phase of your cycle (your fertile phase),
  • Confirm if you are ovulating every cycle – ovulation is a sign of health, you want to make sure it’s happening every month!,
  • Monitor your hormonal health & identify irregularities,
  • Avoid pregnancy without synthetic hormones and side effects, OR increase your chances of achieving pregnancy (depending on your intentions),
  • Get in tune with your body’s natural rhythms.

In this guide, I’ll tell you more about each biomarker, what they are, what they tell you, and why they’re important.

Cervical mucus 

An illustration of a hand showing cervical mucus stretching in between two fingers

Cervical mucus (CM) is the main biomarker. It’s a hydrogel produced in your cervix (the narrow neck-like structure at the base of your uterus), made of mucus molecules, water, enzymes, protein chains, and other compounds.

It’s secreted by your cervical crypts, and it’s affected by hormones estrogen and progesterone. Depending on the hormone present in your body at the time, your cervix will produce two main types of CM: 

  • Estrogen = E-type mucus
  • Progesterone = G-type mucus (gestagenic mucus)

Estrogenic mucus, or E-mucus is critical for fertility because sperm depend on it to survive. In other words, without E mucus, sperm would die pretty quickly in your vagina. During the fertile time of your cycle, E-mucus becomes thin, watery, and stretchy allowing sperm to stay alive for up to 5 days, and move through the cervix to reach the egg.

And the second type is produced when progesterone is present. It’s called gestagenic mucus, or G-type mucus. During the infertile time of your cycle, the g-mucus creates a dense antimicrobial plug to prevent sperm from entering your vagina. It stays high in the cervix, so you perceive it as a dry sensation when you wipe, compared to when estrogenic mucus is present. 

The appearance, color, and consistency of cervical mucus can also provide clues to your reproductive (and overall) health.

Aren’t our cyclical bodies amazing? 😍

LH surge

An illustration of an LH strip

The Luteinizing Hormone (LH) is the hormone that triggers the release of the egg into the fallopian tubes, in other words, it’s the hormone that triggers ovulation.

It surges 24-36 hours before ovulation, and it’s possible to identify it with a home urine test.

LH testing can:

  1. Give you confidence in your biomarker observations;
  2. Help you identify hormonal activity in confusing cycles;
  3. Assist in achieving or avoiding pregnancy.

A few things to consider:

  • The LH surge doesn’t indicate the beginning of the fertile window! Only cervical mucus can do that. But, when used in correlation with cervical mucus, LH is a useful biomarker for identifying peak fertility near ovulation.
  • A positive LH test doesn’t guarantee ovulation or confirm that you did ovulate – it only indicates a surge in the hormone responsible for ovulation. Only a shift in your Basal Body Temperature (BBT) confirms that you actually ovulated.
  • It’s common for folks with PCOS to get a positive test without actually ovulating.

So, while the LH surge can tell you a lot about the fertility status in your cycle, you need to back up a positive test with other biomarkers like cervical mucus and basal body temperature.

Basal body temperature (BBT)

An illustration of a digital thermometer

“Basal” refers to the temperature at rest, which is usually the lowest temperature you will have during the day.

After ovulation, progesterone levels increase. This hormone has a thermogenic effect on the body, causing your temperature to rise and stay high for the rest of the cycle.That’s why it’s a great biomarker to confirm ovulation! 

The rise in BBT in the second half of the cycle happens because one of the jobs of progesterone is to create a warm and nurturing environment in your uterus for the baby to grow.

If there is a pregnancy, the basal body temperature will remain high throughout most of it. If there is no pregnancy, it will drop 12-14 days after ovulation, with the arrival of your next period.

If you take your temperature every morning and record it on a chart, you will notice a clear difference between your pre-ovulatory and post-ovulatory phases. Your BBT will be lower before ovulation and higher after.

BBT can also help you estimate the date of your next period because the length of your luteal phase (the days between ovulation and your next period) stays fairly constant.

Period (and other types of bleedings)

An illustration of a menstrual cup tilted down and blood is flowing out of it

Your period is another important biomarker that gives you important clues about your hormonal levels.

Estrogen and progesterone influence your uterus: 

  •   Before ovulation, estrogen thickens the lining of the uterus (the endometrium).
  • After ovulation, progesterone stops the growth of the endometrium, keeps it in place, and develops secreting glands to nurture a possible pregnancy. At the end of your cycle, progesterone drops, causing the endometrium to shed – in other words, that’s what triggers your period.

As a biomarker, your period indicates the influence of your hormones in the uterine lining. 

The amount, color, and texture of your period reflect the levels of your reproductive hormones (especially estrogen) in your previous cycle. That’s why it’s essential to objectively measure how much you bleed each cycle!

⚠️ the lack of period is also a biomarker indicating low hormonal activity.

🤎 Luteal phase spotting: Sometimes you might see dark or brown spots in the days before your period. In most cases, it’s a sign that your body isn’t producing enough progesterone to maintain your uterine lining during the luteal phase. As a result, the lining starts to shed earlier than expected, and the blood oxidizes in the air.

Tracking your period and spotting can help you understand what’s going on with your body and your hormones. Your menstrual cycle is a vital sign of your health! ❤️

Other relevant symptoms

An illustration of a hand showing cervical mucus stretching in between two fingers

Monitoring symptoms like pain, headaches, fatigue, insomnia, weight gain, acne or mood swings can help you identify if something’s up. These symptoms can be caused by hormonal imbalances, stress, illness, diet or exercise.

Your cycle is an incredible feedback tool, constantly giving you clues about your health and well-being. If you notice any unusual patterns, take the opportunity to investigate if there could be an underlying problem.

Carmen Lorenzana - Free Guide The Four Phases of the Cycle

New to Menstrual Cycle Awareness and not sure where to start?

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