What is LH? Luteinizing Hormone Function, Levels, & Testing

Luteinizing hormone (LH) is arguably one of the most important hormones when it comes to getting pregnant. That’s because it is one of the main hormones responsible for ovulation, and without it, the body is not able to release an egg naturally for fertilization. 

To help you better understand the importance of this hormone and how it works, this post will explore what LH is and what it can tell you about your fertile window. We’ll also cover the best ways to test for LH, what your LH results may mean, and what you can do if your LH levels are too high or too low. 

What is LH (luteinizing hormone)?

Luteinizing hormone, or “LH”, is a type of reproductive hormone that is produced by both men and women. In men, LH helps to stimulate the production of testosterone. In women, LH helps to stimulate the production of estrogen, specifically oestradiol (E2), and then progesterone if ovulation happens.

For the purposes of this article, we will be focusing on LH in women and its role in the menstrual cycle. 

What LH can tell you about your fertile window

LH remains relatively low and stable during the first half of the menstrual cycle. However, 24-36 hours prior to the day of ovulation, LH levels spike dramatically. This sharp increase in LH is often referred to as the “LH surge”, and it is this increase in LH that triggers the body to ovulate. 

Once ovulation is over, LH then falls back to its baseline level. The few days where LH levels are rising and elevated are considered the most fertile days of the fertile window, and it is the window of time during the menstrual cycle where the chances of conception are the highest.

Because LH is so closely linked with ovulation, it is common for women to measure their LH levels as ovulation approaches in order to predict when they are the most fertile. If they are trying to conceive, they can then use this information to plan sex with their partner at the most optimum time of their cycle.

LH fluctuates during your menstrual cycle

LH does not remain at the same level throughout the menstrual cycle. Here’s a look at when you can expect it to be at its lowest and highest. 

When is LH the lowest

If you have a regular cycle and you are not pregnant, LH levels on average tend to be at their lowest during the luteal phase, i.e. just after ovulation. While levels can vary among women, it is common for LH to measure between 0.7 to 12.9 IU/L during the luteal phase, compared to a slightly higher average of 1.9 to 14.6 IU/L during the follicular phase. 

If you are pregnant, LH levels are typically at their lowest (below 1.5 IU/L). 

When is LH the highest

LH levels are at their peak during the middle of the cycle. Again, levels can vary depending on the individual, however, LH typically measures between 12.2-118.0 IU/L around the time of ovulation. 

LH surge

LH levels rise dramatically around 24-36 hours before ovulation. This is known as the “LH surge”, and it is common for LH to measure as high as 118.0 IU/L. While everyone’s cycle is different, the LH surge and ovulation typically occur midway through the menstrual cycle.  

Testing for LH

An LH test is a type of test that measures the amount of luteinizing hormone in your body. Some LH tests can be done at the doctor’s office, while others can be done from the comfort of your home. Here’s a closer look at the various ways that you can measure LH.  

Blood serum test

Taking a blood serum test at your doctor’s office is the most accurate way to measure your LH levels. If you do choose to have this type of test, you will need to make an appointment with your doctor so that you can have a blood sample taken and will then send the sample of your blood off to a lab where it will be tested. After testing is complete, you will receive your results within a few days. 

To track how your LH levels rise and fall over time, you will need to have multiple tests and consultations with your doctor. Because this can be both time-consuming and expensive, blood serum testing is typically only recommended for women struggling to become pregnant, or those experiencing symptoms of hormonal conditions such as PCOS or endometriosis. 

At home urine test

In addition to blood testing at a doctor’s office, it is also possible to measure your LH levels at home with a urine test. Traditionally, the most common testing method used is an ovulation predictor kit, or an “OPK” for short. 

OPK’s are similar to pregnancy tests, but instead of testing for hCG (human chorionic gonadotropin), they test for luteinizing hormone (LH). Specifically, they are designed to confirm if LH levels are considered elevated enough to be “surging”. 

Please note that OPK’s do not measure your exact LH levels. They only give a “yes” or “no” answer about whether or not your LH levels are high enough to be considered surging. For more information on how to read and interpret an OPK, check out our recent article What Does a Positive Ovulation Test Look Like?

If you are looking to see your exact LH levels without the hassle of going to the doctor, hormone testing solutions like the Mira App and Analyzer are a happy medium. This type of at-home testing involves collecting a urine sample, dipping a Mira test wand into the urine sample, and then inserting the wand into the Mira Analyzer. The Mira Analyzer will then present you with your exact LH concentration level. By testing over time, you can become better acquainted with your individual cycle, enabling you to better predict your LH surge and fertile window. 

Why should you monitor LH?

Because LH is so critical to the regulation of the menstrual cycle, there are a few different reasons why it may be necessary to have your LH levels tested regularly:

Fertility issues

If you and your partner are struggling to become pregnant, it is a good idea to have your LH levels checked. This is because at some point midway through your cycle, surging LH levels help to trigger ovulation – which is necessary for conception. By testing for LH, you can get a better idea of whether or not ovulation may happen. 

Determining ovulation

Another reason why you may want to test for LH is to estimate your day of ovulation. This is particularly important if you are planning a pregnancy as your fertile window occurs during the five days leading up to ovulation and the day after ovulation. Within this fertile window, the day of your LH surge and the day of ovulation are considered your “peak” fertility days. 

To maximize your chances of becoming pregnant, doctors typically recommend having sex with your partner as frequently as possible during this window of time. By testing for LH, you can more accurately predict the best times to have sex with your partner in order to become pregnant. 

Menstrual changes

If you notice any changes to your menstrual cycle, you will also want to have your LH levels checked. This is because an imbalance of LH may be an indicator of certain hormonal conditions, such as polycystic ovary syndrome. 

Additionally, if you think that your irregular cycles are due to aging, an LH test alongside other tests can help your doctor confirm whether or not you are undergoing menopause. This is because baseline LH levels are much higher in menopausal women. 

When should you measure LH?

The best time to measure your LH levels is early on in your cycle (approximately a week before ovulation). To see how your baseline LH levels compare to your LH surge, you should aim to test daily during this time. It’s also recommended to test at the same time each day to receive the most accurate results. 

Understanding luteinizing hormone levels in females

While LH levels can vary depending on the individual, there are guidelines for what is considered normal, too high, or too low.

Normal LH levels

In women, LH levels typically remain between 5-25 IU/L. However, there are more specific ranges to be aware of including:

• Follicular phase: 1.9 to 14.6 IU/L
• Luteal phase: 0.7 to 12.9 IU/L
• Midcycle/Ovulation: 12.2-118.0 IU/L
• Pregnancy: <1.5 IU/L
• Menopause: 5.3 to 65.4

 

High LH levels

If your LH levels are above the normal threshold, this could indicate any of the following:

• Ovulation disturbances
• Polycystic ovary syndrome (PCOS)
• Turner syndrome
• Menopause

To determine the exact reasons behind why your LH levels are too high, your doctor will likely want to run further testing. They can then provide further advice on what to do in your individual situation.

Low LH levels

If LH levels are below the normal threshold, this could indicate:

• Hypopituitarism
• Malnourishment 
• Eating disorders

Again, your doctor will want to run further testing to determine the specific cause of your low LH levels so that they can provide you with the best advice for your situation. 

LH (Luteinizing Hormone) FAQs