Solving the fertility equation

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With all the charts and data, sometimes TTC feels like it requires a degree in math. We’re breaking down the fertility equation to help you understand how it all adds up.

Why do we need math to have babies?

A healthy couple has only a 25% chance of conceiving on any given cycle. Everything you do, from lifestyle changes to ovulation tracking to taking fertility supplements, is about optimizing that chance. And probability requires math!

Depending on the kind of information you enter into Ovia, like previous cycle data or OPK results, we might only be predicting your fertile window. But the fertile window is just one part of the equation.

For a more complete equation, we’ll need more than fertile window prediction…maybe something like:

Confirmation + 24-hour ovulation prediction + cycle events = fertile window prediction

The goal is to understand when you’re at your most fertile so you can aim to have intercourse at the best time each month. Now that we have a formula for that, we can break down each part of the equation to better understand it.


Confirming if and when you ovulate provides the basis for understanding what your cycle looks like.

Some studies have shown that 70% of women don’t ovulate right in the middle of their cycle or ovulate at different times each cycle.1 It is essential to confirm ovulation to understand how regular your cycle is and help identify any underlying conditions that might affect your fertility.

You can confirm ovulation at home using oral or skin-based temperature checks. Your doctor may also recommend a blood progesterone test — although the ASRM (American Society of Reproduction) says this has to be performed seven days prior to the onset of the next period to ensure it’s detecting ovulation correctly. However, the most accurate way to confirm ovulation is either with consecutive transvaginal ultrasounds performed by your doctor or with a metric called “core body temperature,” which you can do with OvuSense.

As we mentioned, your temperature increases around the time of ovulation. Most methods of tracking this increase monitor basal body temperature (or “resting temperature”) over the course of a cycle. That’s one of the many things you can track in Ovia.

That change in body temperature during ovulation is really small and easy to miss, even if you’re checking every morning. So if you’d like an even more accurate method of monitoring temperature change, OvuSense uses core body temperature.

Rather than take your temperature every morning, OvuSense uses a medical-grade vaginal sensor the size of a tampon that checks your temperature while you sleep. By carefully mapping core body temperature (CBT) over a prolonged period, the clinical studies produced by the team at OvuSense report that it’s able to confirm ovulation with 99% accuracy. OvuSense was built to spot this tiny increase in body temperature by measuring your CBT every five minutes throughout the whole night. It’s this difference that provides the clinically proven 99% ovulation confirmation accuracy, compared to the 69 to 86% accuracy you can achieve with typical basal body measurement, skin-worn sensors, or a fertility bracelet.2

+ 24-hour prediction

The second major part of the fertility equation is 24-hour prediction. You can measure this using a urine test for luteinizing hormone (to measure your “LH surge”), or again by using OvuSense.

As the body prepares to release an egg, there is a pulse (or surge) of LH, which kicks off the ovulation process. The LH peak generally occurs 24 to 48 hours in advance of ovulation. OvuSense can also predict using the data in the current cycle by looking at the early rise in progesterone release that occurs as ovulation starts. OvuSense reports clinical studies that show this has an accuracy of 89%, compared with 74 to 84% for LH urine strips.4

While very helpful in predicting ovulation, LH surge can’t confirm it. This is especially true for women with PCOS (because their hormone levels can differ) and for those with irregular cycles (because knowing exactly when to test LH can be difficult).

Monitoring your cycle at home is now more important than ever, especially in these times. The team at OvuSense just launched a new product, OvuSense® Pro. It allows OvuSense users and their doctors to remotely access detailed cycle information through an online portal. Based on novel clinical research3, it provides unique key analysis about cycle patterns to help medical professionals know whether they need to carry out further tests, know what effect medications are having, time tests like blood progesterone and ultrasounds, understand what’s happening during treatment, and understand whether medications, treatment, or dietary change are having an effect on the timing of ovulation and the length of cycles.

= Fertile window prediction

The key to your fertility success is combining an understanding of confirmation with 24-hour prediction, along with tracking other events in your cycle to produce an accurate understanding of your fertile window. That’s where Ovia comes in — picking up on all this key information in your equation to help you time your intercourse and maximize your chances of success.

One last equation

If you’d like to try tracking your core body temperature, but you’re feeling a bit divided, OvuSense has an equation of their own that can make your calculations easier:

90 days + no confirmation = 100% money-back

Basically, if you use OvuSense for 90 days and their system isn’t able to accurately detect and confirm your ovulation, you’ll receive a full refund.

To learn more about OvuSense, including their round-the-clock technical and fertility support, and how you can use core body temperature tracking to both predict and confirm ovulation, tap below.

Learn more about OvuSense

This ad is brought to you by OvuSense

  1. Baird D, McConnaughey D (1995); Lenton EA, Landgren BM (1984a); Lenton EA, Landgren BM (1984b)
  2. Papaioannou S, Delkos D, Pardey J (2014); Freundl G, Godehardt E (2003); Barron M L Fehring R (2005); Bauman JE (1981)
  3. Karoshi M, Hurst B (2020); Hurst BS, Pirrie A (2019)
  4. Papaioannou S, Delkos D, Pardey J (2014); McGovern PG, Myers ER (2004); Irons DW, Singh M (1994); Lloyd R, Coulman CB (1989)
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