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What’s up with Ovulation Predictor Kits? (The low-down on OPKs)

What is an Ovulation Predictor Kit/LH test?

OPKs are at-home tests which assess the Luteinizing Hormone (LH) levels in your urine. The levels detected in your urine seem to appear about 3-6 hours after it can be initially assessed in your blood, which makes these tests pretty accurate for at-home use. People will assess their Luteinizing Hormone levels to determine when their bodies are shifting towards ovulation, which can be helpful when someone is looking to time intercourse accurately when trying to conceive.

How, why and when does LH rise?

LH rises in response to a rapid increase in estrogen (estradiol). Estrogen rises as the follicle (the sack that surrounds the maturing egg) grows. So, in other words, we make estrogen from the eggs that our ovaries are growing. This happens in response to a rise and steady stream of Follicle Stimulating Hormone (FSH) in the blood, which comes as a signal from the pituitary gland in the brain. As estrogen levels begin to rise rapidly, in response to the egg cells and follicles growing, the pituitary gland begins to release increasing pulses of Luteinizing Hormone. This rise in LH helps to finalize the maturation of the egg and thins the wall of the ovary (via enzymatic activity) to help it more easily rupture through - A.K.A. ovulation.

What technically is an LH “rise”, “surge” or “peak”?

An LH rise is simply that - a detectable elevation from the baseline during the follicular phase (before we ovulate). Whereas the LH “surge” is the day that the level crosses a specific threshold, and the “peak” is the last day that it is at this high level. We often use the peak day as a marker to compare and predict where ovulation may occur. Because, remember, LH rises before ovulation occurs. Different studies (and different products) measure the surge differently. It could be a detectable rise in LH levels anywhere from 2.2 to 16 fold compared to the mean of the previous 7 days measured.

And just like the rise is different than the surge, there are different types of LH rise and surge patterns…

Some people (42.9%) will experience a rapid rise, where as most people (57.1%) will have a more gradual rise with a surge that either then spikes (42-48%), is bi-phasic (33-44%) - meaning there’s a rise, a fall and then a second rise, or shows up as a plateau (11-15%) - meaning that the rise is sustained for a few days. The average range of days with elevated LH is 3-11 days. What this means is that observing an initial rise, or even a surge, does not mean you won’t detect another surge or peak in the days (or even weeks) to come.

OPKs do not confirm ovulation and it is possible to observe more than one LH surge in a cycle.

You can also observe an LH surge without any ovulation occurring. It’s not uncommon for me to hear people refer to these tests as “ovulation tests”. They are marketed as ovulation predictor kits. It’s just a prediction and it’s not a confirmation. So seeing that rise does not necessarily mean that ovulation is imminent. While it can be for some people’s bodies and some cycles, the range of where ovulation may occur in comparison to the LH surge is quite wide.

When does ovulation happen in relationship to an LH surge?

There’s a whole range of where ovulation occurs in relationship to the LH surge, and this differs not only from one person’s body to the next, but can also shift from one cycle to another.

Most research shows that ovulation occurs within 16-48 hours after the initial LH rise, but studies have shown ovulation occurring 6 days prior to the LH Peak (during the initial rise) or up to 5 days after the Peak (during its gradual decline).

Now, I only share this data to illustrate the range of human experience and the importance of understanding the gray zone between the black and white digital data that we might think we are receiving from ovulation predictor kits.

And to get a bit more specific, most studies indicate that ovulation occurs within 10-24 hours after a Peak LH reading, so identifying the Peak day rather than just the rise can be helpful.

Why do people use these tests for preconception?

There are several reasons why people use these tests when trying to conceive. As a Fertility Educator, I would say that most people use them because they are commercially available, easy to access, and easy to use. I also think that it’s because most of us weren’t taught about observing changes in cervical mucus as a tool of fertility awareness. However, cervical mucus is necessary for sperm transport and the days that we observe cervical mucus are the active days of fertility. Not everyone’s body will align their days of mucus with the LH rise and surge days. Optimally, these range of days overlap. However, some people’s bodies will produce cervical mucus for a few days, that mucus will go away for a day or two, and then their bodies will ovulate. If they detected an LH peak the day before ovulation and they timed intercourse on that day and the day of ovulation (what would be considered the statistically “most fertile” days), they would have missed the timeframe of optimal sperm transport (i.e. days with observable cervical mucus).

Therefore, I always encourage people to time intercourse based on their in-real-time observations of cervical mucus when trying to conceive.

When there is limited mucus observed (less than 3 days) or continuous mucus (more than 7 days), using an LH test can help to identify the pre-ovulatory fertile window. 

Can these be used to avoid conceiving?

It is not advisable to use these tests on their own as a way to prevent pregnancy. There are Fertility Awareness Methods that use hormone assessment, like OPKs, but they are used in conjunction with a calculation based on several cycles worth of data for that individual. As mentioned above, sperm cells are able to actively transport into the cervix and uterus via cervical mucus. For the majority of the cycle the vaginal environment is too acidic for sperm cells to survive. However, cervical mucus is more alkaline and temporarily shifts the environment of the vagina to make it hospitable for sperm. In addition to this pH shift, the cervical mucus helps to actively transport the sperm cells and produces sugars and proteins to keep them alive within the reproductive system for 3-5 days. Therefore, it is imperative to avoid having intercourse on days with active cervical mucus to successfully avoid pregnancy. And since the LH tests do not detect cervical mucus, and cervical mucus does not always line up with an LH rise or surge, it is not advisable to use these tests for contraceptive purposes.

So how do you confirm ovulation?

If the LH tests do not confirm ovulation, how do we know that our body has ovulated? With the exception of an ultrasound assessment on the day before, during and after ovulation, the only ways that we can confirm ovulation are through assessing progesterone levels via blood or urine, or tracking our Basal Body Temperature (BBT). Our bodies produce sustained elevated levels of progesterone only after ovulation. Therefore, we can use urinary or blood assessments of progesterone shortly after suspected ovulation. Progesterone causes our body’s metabolism to increase, which creates a subtle shift to a higher temperature reading post ovulation. When we are tracking our BBT, we want to take our temperature first thing in the morning (before we get out of bed) every day throughout the cycle. Once we see at least 3 elevated temperatures (0.2 degrees F) that are all higher than the previous 6 temperatures, we can confirm ovulation.

(Want to learn more about BBT tracking? Check out this blog post.)

Do I encourage people to use OPKs?

Sometimes! There are several scenarios where assessing LH surges can be helpful - especially when someone is trying to conceive. However, I look at it as a data point…and the more sets of data we are able to collect, the more detailed our body’s story can be. I don’t look at these tests as the be-all-end-all, but they can be a handy data point to work with when assessing the preovulatory window. When folks work with me to chart their cycles, sometimes we will add the statistical range of ovulation based on Peak LH readings alongside the Peak Day of mucus and the BBT rise to more clearly identify the likely day of ovulation (retrospectively). But because LH tests do not confirm ovulation and they do not assess for the active days of fertility/sperm transport, I do not consider LH testing to be a necessary data point to work with when assessing ovulation.

Want to learn more about your body’s LH surge and production of progesterone at home? Check out the Predict (LH) and Confirm (PdG - progesterone) tests from Proov. And feel free to use my affiliate code DARCIE to get 20% off!

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