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Progesterone and Peak Fertility – What your doctor is not telling you

Progesterone and Peak Fertility: When should you test your progesterone?


Progesterone is one of the most important hormones for fertility. Progesterone is only produced naturally in the body after ovulation and is essential for uterine stability. Progesterone, aka ‘pro-gestation’ hormone helps thicken the endometrial lining and aids in the formation of new blood vessels.1 Both of these functions are necessary for healthy implantation of the embryo. If you have been struggling to get pregnant or suffer from recurrent miscarriages, it is possible that your progesterone levels are too low and/or your luteal phase is too short to support a viable pregnancy.1


What are common signs of low progesterone?

  1. Luteal phase consistently less than 10 days in length2
  2. Spotting before your period begins2
  3. Miscarriage
  4. Heavy cycles
  5. Shorter cycles (luteal phase defect)


Conventional Testing for Progesterone Levels

Unfortunately, there is a common error that occurs when testing progesterone levels. Many fertility specialists only order blood work for mid-luteal progesterone on Day 21. There is a major flaw with this method as it assumes you are ovulating on day 14. However, only about 13% of women actually ovulate on day 14 of their cycle!2 This is due to the huge variability in the length of the follicular phase, which occurs before ovulation. This means testing mid-luteal progesterone on day 21 can be an extremely unreliable method.


A Better Way: Peak plus 7 NOT Day 21

Tracking your cycle to know when your luteal phase begins allows for a more accurate measurement of progesterone levels. Understanding your cycle is crucial in determining correct hormone therapy dosages, and also ensuring progesterone levels are rising sufficiently to sustain a pregnancy. This natural treatment for infertility is very inexpensive and easy to do. As a Naturopathic Doctor, the Peak plus 7 is a valuable fertility tool I use with my patients. The Peak plus 7 method for testing mid-luteal progesterone takes into account each woman’s unique biology, and can determine if your corpus luteum and uterus are producing adequate progesterone.3 Testing on day Peak plus 7 provides a much more accurate representation of your true mid-luteal progesterone levels.


How do I Know When my Peak Day Occurs?

Your Peak day is the last day of sperm-friendly cervical mucus, not ovulation. Fertile cervical mucus is clear and stretchy in nature, similar to an egg white.4 It has a slippery sensation when you wipe with toilet paper, and you can stretch it between two fingers. If you have irregular cycles, you may notice that your fertile cervical mucus starts and stops during the follicular phase. You need at least 3-5 consecutive days of fertile cervical mucus to accurately determine your Peak day.4 An easy way to track your cycle is using an app called MyFlo. MyFlo is a functional medicine period tracker and hormone balancing app created by Alisa Vitti, CHC. MyFlo allows you to track your cycle length, cervical mucus and premenstrual symptoms all in one place. Another tool I use commonly with my patients is the Daysy fertility tracker that will easily tell you when you ovulate.


How do I know if I ovulated?

Measuring your basal body temperature (BBT) is a useful tool for confirming, not predicting, ovulation each cycle. BBT rises after ovulation, and stays high if pregnancy is achieved. Basal body temperature must be taken at the same time every morning after at least 5 hours of continuous sleep.4 For the most accurate reading, take your temperature as soon as you wake up, even before you get out of bed! Be sure to use a BBT thermometer that has increased accuracy, such as this one. This is what the Daysy tracker does.


What is an Ideal Luteal Phase Length?

The ideal luteal phase length is 10-16 days or 13 +/- 3 days. A luteal phase shorter than ten days is often indicative of low progesterone levels. Without a long enough luteal phase, the uterine lining becomes compromised and the embryo cannot implant properly.5 If you are currently tracking your cycle and undergoing fertility treatments, talk to your doctor about testing progesterone on your Peak plus 7 instead of day 21.


What should my progesterone levels be on Peak plus 7?

Ideal Peak plus 7 progesterone levels should be at least 19.1ng/ml or 60.74nmol/L.1


My next blog post will focus on simple steps you can do every day to help increase progesterone levels.



  1. Dr. Nora Pope, ND. (2017) Cycle Charting & Progesterone BHRT. [Webinar]. Retrieved from
  2. Dr. Nora Pope, ND. Day 21 No More. Published 2014.
  3. Hilgers TW, Daly KD, Prebil AM, Hilgers SK. Cumulative pregnancy rates in patients with apparently normal fertility and fertility focused intercourse. J Repro Med. 1992, 37(10):864-6.
  4. Fertility Friday. Charting Basics. Published 2014.

5.Csapo AI, Pulkkinen MO, Ruttner B, Sauvage AP, Wiest WG. The significance of the human corpus luteum in pregnancy maintenance:                  Preliminary studies. American Journal of Obstetrics and Gynaecology. 1972, 112(8): 1061-1067.

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