Luteinizing Hormone - What LH tests (OPK’s) are looking for!

Woman with red fingernails holds a calendar and an LH test and points to a calendar with the seventeenth of the month circled in red.

What is Luteinizing hormone (LH)

Luteinizing hormone (LH) plays a key role in ovulation and the menstrual cycle. It is an important hormone for women’s reproductive health and is crucial in regulating a woman’s cycle. LH is the hormone which signals the ovaries to release an egg and prepare the uterus for pregnancy. A surge in LH levels triggers ovulation - the release of an egg from the ovary, which is why LH tests are often used to track ovulation.

After ovulation, LH continues to play a role by stimulating the production of progesterone, which helps prepare the uterus for pregnancy. If the egg is not fertilized, LH and progesterone levels eventually drop, triggering the start of a new menstrual cycle

What are LH tests and how do they work?

LH tests, which are also known as OPKs (Ovulation Prediction Kits), are used to predict ovulation so that a woman knows when she is most fertile and likely to get pregnant. OPK’s show that LH levels are rising and that the body is preparing to ovulate. The tests look and function just like home pregnancy tests. A test typically involves peeing on a test strip which measures the concentration of LH in the urine and waiting for the lines to appear. They work by detecting the surge in luteinizing hormone (LH) that occurs just before ovulation. A positive result means that your LH levels are rising, and you can expect to ovulate within the next 24-48 hours.

The idea of the LH test is that you can predict ovulation by monitoring your LH levels. Ovulation is actually a process which lasts several hours, it starts when a surge in luteinising hormone levels causes the ovarian follicle to tear and release a mature oocyte (egg) from the ovary. This basically means that ovulation is triggered by a high level of the LH hormone. If you monitor your LH levels, you should be able to see this rise in LH which shows that the body has begun the process of ovulation. This is especially useful if you want to get pregnant and need to know when you are most fertile.

To use an LH test correctly you should know what phase of your cycle you are currently in. This is because you should be testing every day during your fertile window, and ideally the tests should be done at approximately the same time and under the same conditions each day. Tracking your cycle with the femSense app means that you will always know when you are beginning your fertile period.

How exact are they?

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 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.

According to one study, the LH peak is on average 1.2 days before ovulation. In a quarter of the cycles studied, the time between the LH peak and ovulation was longer than two days. This means that LH tests can provide a rough guideline as to when ovulation takes place, but they cannot confirm it.

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Combining OPK’s with femSense

While using OPKs with femSense isn’t required, combining the two methods of ovulation can be really helpful in identifying the most fertile days in the month. When you combine femSense with OPKs, you’re keeping an eye on two different signals from your body that help detect ovulation. You can add LH test results to the femSense app so that you can see in your personal history when your LH levels surge before ovulation.

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 confused if the results appear to conflict.

Ovulation is a complex process which lasts up to 24 hours, but the body is preparing to ovulate for even longer. LH surge typically occurs 24 – 48 hours before ovulation and traces of the hormone can be detected in urine. This is what LH ovulation tests are looking for. After ovulation your progesterone levels rise which causes your body temperature to rise too. It is this tiny rise in temperature that femSense can detect. The rise in temperature is a direct result of ovulation and that is why only the temperature method can confirm ovulation. Once you have ovulated you are fertile for approximately 24 hours.

In short: LH tests measure a rise in hormone levels BEFORE ovulation while femSense uses the temperature method to detect the rise in temperature that happens AFTER ovulation. This is why these two different methods may show results on different days during your fertile window.

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.