The Problem of the 28 Day Cycle Myth

In part 1 of this series we learned about what the 28 day cycle myth is and why it’s wrong. Now let’s take a look at the problems that can come from following the 28 day cycle model. If you haven’t read the first part of this series, go back and read What is the 28 Day Cycle Myth?.

Problem #1: If you assume you ovulate on cycle day 14 you may miss the optimal time to try to conceive.

Some people don’t ovulate until later in the follicular phase; ovulation between days 16 and 18, or even later, is not uncommon. If you are timing baby-making sex around CD14 you may completely miss your time of ovulation and greatly reduce your chances of conception.

Problem #2: Basing hormone testing on a 14 day luteal phase can give you inaccurate results.

If you are experiencing difficult symptoms of PMS or difficulty in conceiving, your doctor may recommend that you get progesterone tested. There are two ways the timing of this testing is commonly recommended.

You may be told you need testing on CD21 or 7 days post ovulation, and you probably won’t get an explanation. The reason goes back to the assumption that you have a 28 day cycle. The ideal time to test progesterone is in the middle of the luteal phase when progesterone reaches its peak. Which you can see in the pink below.

Let’s break this down. If you have a 28 day cycle and ovulate on CD14, the middle of your luteal phase would be considered CD21, or 7 DPO.

But what if you have cycles longer than 28 days?

Look back at the hormone chart above with the progesterone peak falling in the middle of the luteal phase. If your cycle is 33 days and your luteal phase is 14 days, you would test 7 days after ovulation. This would fall on cycle day 26 rather than cycle day 21. If you test on cycle day 21 rather than in the middle of your luteal phase, your testing would be earlier on the progesterone incline and may appear artificially low in your results.

What if your luteal phase is not 14 days?

As previously mentioned, luteal phases can last anywhere from 4 days to 17 days. If you have a 28 day cycle but your luteal phase is only 10 days and you ovulate on CD18, the middle of the luteal phase would be CD23, or 5 DPO. Testing on cycle day 21 would be too early and testing 7 days post ovulation would be too late.

The 14 day luteal phase myth is so pervasive that holistic health practitioners and fertility awareness advocates continue to recommend progesterone testing on 7 DPO. Despite the awareness that not everyone experiences a 14 day luteal phase.

Progesterone testing should be based on the individual; testing on cycle day 21, or 7 days post ovulation will not be accurate for everyone.

Problem #3: Assuming you ovulate on cycle day 14 may lead to inaccurate pregnancy due dates.

Pregnancy due dates are most commonly based on the first day of your last menstrual period, which assumes you ovulate on CD14. This method of calculating the due date takes the first day of your last menstrual period and adds 280 days.

If you happen to ovulate on CD21 rather than CD14, that puts you a whole week behind assumed timing. Ovulating and conceiving later than the assumed time can potentially cause some issues, including early ultrasounds with baby measuring “small”. Or early induction under the assumption that baby is overdue.

The best way to determine due date is to chart your cycles with a reputable Fertility Awareness Method and base your calculation on day of ovulation.

How can you know when you ovulate and how long your phases are to prevent these problems?

To put it in the simplest way I can, learning a reputable Fertility Awareness Method can help you identify ovulation, optimal days to try to conceive, optimal days to do hormone testing, hormonal imbalances, and more.

With as little as a thermometer and pen and paper you can gain deep insight into your personal cycles. Taking Charge of Your Fertility by Toni Weschler is a great book for learning a Fertility Awareness Method on your own.

If you would prefer to learn FAM from an educator, I offer 2 options for this. I offer the Cycle Charting Walkthrough program which teaches you everything you need to know to chart on your own. Or I also offer the Cycle Charting Walkthrough in addition to a support plan for conception or managing health issues. You can see more about the options available here.

Body literacy is incredibly empowering and I want everyone to have access to that. Have you experienced any of these problems? Have any questions? Let us know in the comments below!



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