Ovulation test strips (OPKs) and femSense often show ovulation on different days – and that’s OK.

Young woman reading in bed with her legs held high in the air, surrounded with OPK symbols

How can it be that ovulation test strips and femSense sometimes show ovulation on different days? You only ovulate on one day! In actual fact it makes perfect sense when you understand how ovulation tests work. The two different methods of ovulation detection are measuring different bodily signals which indicate ovulation, and these signals occur at different stages of your fertile window. It begins with a hormonal surge at the beginning of the fertile window to ripen a maturing egg and ends with the release of the egg at ovulation.

While ovulation test strips measure that the body is preparing to ovulate, femSense uses the temperature method to measure and confirm that ovulation has taken place. In other words, LH tests are measuring the beginning of the fertile window and the temperature method is measuring the end.

But let’s break it down to how each method works, what bodily signals are being measured and what information each can give you about your ovulation.

What is an Ovulation Test?

Ovulation tests are used to determine when you ovulate and are most likely to get pregnant. There are several different home tests used to predict and measure ovulation including ovulation tests strips (ovulation prediction kits), cervical mucus monitoring or the temperature method. Each method measures a different bodily signal that shows a woman is in her most fertile phase.

Ovulation Test Strips (OPK’s)

Ovulation test strips, otherwise known as Ovulation Prediction Kits (OPK’s), are strips or sticks that you pee on to measure hormones in your urine that indicate that your body will ovulate in the next few days. They are used in the days before ovulation and tell you that your body is preparing to ovulate. Ovulation test strips measure the LH (Luteinizing Hormone) concentration in the urine. LH levels rise in the days before ovulation, and a surge in the LH hormone level triggers the release of an egg. This LH surge typically occurs 24 to 40 hours before ovulation. In short, ovulation test strips predict ovulation a day or two before it occurs.

The Temperature Method

femSense uses the temperature method to measure and confirm ovulation. At ovulation a woman’s basal body temperature rises by a tiny amount and remains slightly higher for the second half of her cycle. The higher levels of progesterone in the second half of the cycle, which cause this tiny rise in temperature, are released by the corpus luteum, the remains of the ovarian follicle that released a mature egg during ovulation. This minute rise in body temperature is therefore a direct result of ovulation and is a reliable indication that ovulation has occurred. If ovulation had not taken place there would be no rise in temperature.

In short, the temperature method detects ovulation after it has happened. If fact the temperature method is the only “home test” that can confirm ovulation.

Using OPK’s and femSense together

The femSense app can predict the beginning of your fertile window and then the femSense sensor patch can measure and confirm your ovulation. This means that femSense can do all the hard work for you. femSense users don’t need to pee on sticks, take their temperature or analyse charts to measure their ovulation. The app will tell you when you are most fertile and most likely to get pregnant. However, we know that many of our users who are using femSense to get pregnant, want to use all the tools available to them to help them get pregnant as quickly as possible. Perfectly understandable! Once you have made the decision to have a baby it can’t happen fast enough. In this situation ovulation tests and femSense can be used together to confirm your entire fertile window from start to finish – it is not necessary, but they can complement each other. Just please keep in mind that they are measuring different phases of your fertile window and don’t be disheartened when the results appear to conflict.

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For women praticing fertility awareness please be aware that OPK’s are not a reliable form of birth control. Unfortunately, LH tests are not always entirely accurate or reliable because the results can be influenced too easily. For example, the LH concentration in urine is higher in the morning than during the rest of the day and the LH concentration is diluted when you drink a lot.

The increase in LH levels before ovulation also varies from woman to woman, which is why the less sensitive tests cannot detect the elevation, but the more sensitive tests can give a false positive.

Scientists have also discovered that some women have several LH surges in one cycle, but because a woman only ovulates once in a cycle you cannot therefore associate ovulation with all those LH level surges. An OPK would detect these surges and incorrectly predict ovulation. For more detailed information you can visit our blog here.

To get a better overview of your cycle length, your fertile window and whether or not you ovulate just track your cycle. Download the free femSense app to track your cycle and use the sensor patches to track your fertility and confirm ovulation.

Sources:

https://www.reproductivefacts.org/news-and-publications/patient-fact-sheets-and-booklets/documents/fact-sheets-and-info-booklets/am-i-ovulating/

https://www.healthline.com/health/pregnancy/lh-surge

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5689497/