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Are you TTC and tracking ovulation? If so, luteinizing hormone (LH) is likely on your radar. After all, LH is the spark that triggers ovulation. And without ovulation, you can’t get pregnant!
Ovulation tests detect LH in your pee to predict when you’ll ovulate. This gives you a heads-up so you know when to have sex if you want sperm and egg to meet.
LH tests can be a game-changer for your fertility journey. But they’re not as simple as they seem. LH has two subunits: alpha LH and beta LH—and your results can vary depending on which one is tested.
Curious how alpha and beta LH compare? Read on—we’ll break down how they differ and what you can do to get the most accurate results.
Takeaways
- Luteinizing hormone (LH) is the reproductive hormone that triggers ovulation.
- Ovulation occurs about 24-36 hours after LH starts rising. The LH surge is what prompts the follicle to release the egg.
- Two subunits make up LH: alpha LH and beta LH.
- The structure of alpha LH is identical to the alpha units of FSH, TSH, and hCG. This can lead to cross-reaction if a test measures alpha LH.
- The beta subunits of these hormones are different and help tell them apart.
- Testing your LH can help you pinpoint your fertile days, so you have the best chance of conception.
- Most OPKs measure alpha LH, which can lead to false results.
- The Inito fertility monitor measures beta LH, as well as estrogen, PdG, and FSH. This means better accuracy, less chance of cross-reactivity, a clearer picture of your fertile window, and accurately confirming ovulation.
What is luteinizing hormone?
Luteinizing hormone, or LH for short, is a fertility hormone secreted by your pituitary gland. It helps regulate the menstrual cycle and plays an important role in reproduction.
But luteinizing hormone’s main function is to trigger ovulation.
LH works as a team with its sister hormone follicle stimulating hormone (FSH). Together, they control the ovulation process. FSH stimulates the growth of ovarian follicles, while LH sets ovulation in motion. Read on to know how.
How does LH affect ovulation?
Let’s take a look at your menstrual cycle to understand.
During your follicular phase, FSH stimulates a batch of ovarian follicles to develop. Inside each follicle is an immature egg.
Typically, one follicle matures faster than the others. This follicle, known as the ‘dominant follicle’ prepares for release while the others wither away.
The egg’s release depends on LH. Throughout most of your menstrual cycle, luteinizing hormone stays low.
But LH levels begin to rise rapidly to trigger ovulation. This is known as an LH surge. Ovulation occurs roughly 24-36 hours after LH rising or 8-20 hours after LH peaks. It happens during the follicular phase of your menstrual cycle (between your period and ovulation).
The LH surge is what triggers the follicle to release the mature egg.
After the egg is released, the empty follicle then forms the corpus luteum, which produces progesterone. This nourishes the uterine lining to prepare for a potential pregnancy.
Once released, the egg travels into the fallopian tubes where it waits to meet the sperm.
If the timing’s right and a sperm greets the egg, fertilization may occur. But if the egg isn’t fertilized within 12-24 hours of ovulation, your next period will likely be around the corner.
LH tests pinpoint your LH surge to predict when ovulation will happen. That way, you know when to head to the bedroom for the best chance of conception.
The problem is since LH has two subunits, interpreting these tests can be tricky.
Alpha LH vs beta LH: what’s the difference?
As mentioned, luteinizing hormone has two subunits: alpha LH and beta LH.
The main difference between alpha and beta LH is that the beta subunit is unique, while the alpha subunit is not.
Here’s what we mean:
LH, FSH, thyroid stimulating hormone (TSH) and human chorionic gonadotropin (hCG) are all glycoprotein hormones. They’re made from similar genes and have similar properties.
This is where things get confusing. The alpha subunit of LH is identical to the alpha subunit of FSH, TSH, and hCG. That’s right— identical!
The good news? The beta subunits are different and help set each hormone apart. The chart below will show you what I mean:
As you can see, the alpha subunits (the light blue ones) are the same. But the beta (yellow) ones aren’t.
Knowing the difference between the subunits is crucial, as it can impact your results.
LH cross-reactivity: Why it happens
Most ovulation predictor kits (OPKs) measure the alpha subunit of LH. Unfortunately, this can set the stage for confusion.
Since the alpha subunits of LH, FSH, TSH, and hCG are the same, there’s more chance of cross-reaction.
For example, say you use an OPK that measures alpha LH. If your FSH or TSH is high, the test could mistake it for LH and give you a positive result—even if ovulation is not around the corner!
This could cause you to stop testing and miss your true LH surge and your fertile window that month.
Learn More: False LH Surge Before the Real One
That’s why Inito measures beta LH instead of alpha LH. Targeting the beta subunit improves accuracy and reduces the risk of cross-reactivity.
How does this affect ovulation testing?
Using a regular OPK that measures alpha LH may lead to false results. If any of the following apply to you, measuring beta LH can help you get a more accurate read on your hormones:
LH levels are lower than the average threshold
Most OPKs base results around average thresholds. If your LH passes that threshold, you get a positive ovulation test. Tests vary, but the average threshold is usually between 25 and 30 mIU/ml or 20-40 mIU/ml depending on the brand type.
If your LH levels are average this may work fine. But if your LH levels are lower than the norm, you could get a false negative.
Here’s what I mean. In one study, LH levels as low as 6.5 mIU/mL still triggered ovulation. Clearly, that’s way below the average threshold and would yield a false negative. That’s why you can’t trust the results on threshold-based tests if your LH levels tend to run low.
Learn more: LH Levels and Surges: What’s a ‘Normal’ LH Level Look Like?
High LH levels
On the flip side, if your LH levels are higher than the norm, it can also skew your results. This is often the case for those with polycystic ovary syndrome (PCOS).
Women with PCOS tend to have high levels of androgens as well as high LH levels throughout their menstrual cycle.
If baseline LH levels cross the average threshold, it can lead to a false positive result on an OPK.
Learn More: Using Ovulation Tests With PCOS: Can You Trust the Accuracy?
Fluctuating LH levels
If you’re using an OPK and your LH levels seem all over the map, the non-specificity of the OPK may be to blame.
Since the alpha subunits are similar in structure, it can alter your results. Using a test that measures beta LH can help you avoid this.
Multiple LH surges
Not all LH surges look the same. Some surges have one LH peak, while others have two or more. For example, in one study 33% of surges had two LH peaks and 8% had more than two!
No matter what your LH surge looks like, the final surge is what triggers ovulation. This means if you have more than one LH peak and use an OPK, things can get confusing. It can be hard to tell which is your “true” surge.
Learn more: Two LH Surges a Week Apart: What Does it Mean?
Anovulation
OPKs predict ovulation. But they don’t guarantee it happened. Around a third of all menstrual cycles are anovulatory. Meaning, ovulation didn’t occur.
If you have an anovulatory cycle and use an OPK that targets alpha LH, you could get a false positive due to cross-reaction.
Now add to this mix the chances of cross-reaction between alpha LH and alpha FSH or alpha TSH. You are in for a confusing ride trying to decipher the information on these LH strips.
The solution? Choose a test that measures beta LH like Inito so there’s less chance of cross-reactivity.
Learn more: Anovulation: Everything you need to know about the #1 cause of infertility
How can I track my LH surge?
Testing your LH regularly is one of the most valuable ways to track your fertility. Here are a few options to monitor your LH:
LH blood test
Blood tests are the most accurate way to measure your LH levels. But they’re not super convenient. Each blood test requires a trip to your doctor’s office or a lab.
Many women trying to conceive take 10-15 LH tests a month, so this can add up quickly.
Not to mention, that’s a lot of needles! Blood tests also take time to process and analyze. This means by the time you get your results, your fertile days may have passed.
OPKs
Ovulation predictor kits (OPKs) can be done at home, so they’re far more convenient than blood tests. They measure LH in your urine to pin down when the surge occurs.
While convenient, OPKs do have their flaws. As mentioned, most OPKS are threshold-based, which can pose problems if your LH levels are outside the norm. Plus, most OPKs measure alpha LH, which can up the chance of cross-reactivity.
Learn more: How Accurate Are Ovulation Tests?
Inito fertility monitor
The Inito Fertility Monitor also lets you track your LH surge and predict ovulation from the comfort of your home. Instead of basing results on thresholds, Inito gives your actual hormone values. You can view your results with personalized charts on our easy-to-use app so there’s no guesswork. Inito also measures beta LH, instead of alpha LH, there’s less risk of cross-reaction.
On top of that, Inito measures estrogen, FSH, and PdG (a metabolite of progesterone), all from one test strip. This gives you a fuller picture of your fertile window than LH alone. And since progesterone and PdG rise after ovulation, Inito can confirm ovulation occurred.
Remember, while ovulation tests can be helpful in the TTC journey, they’re just one piece of the puzzle. It’s important to consider other factors, like nutrition, lifestyle, and any underlying health conditions when trying to conceive.
FAQs
Alpha LH and beta LH are two subunits of luteinizing hormone. Alpha LH is the same as the alpha units of other hormones like FSH, thyroid stimulating hormone (TSH), and human chorionic gonadotropin (hCG). The beta subunits are unique and give each hormone their distinct properties.
Normal mid-cycle LH levels fall anywhere between 21.9 IU/mL to 56.6 IU/mL. That said, studies show that ovulation can be triggered by LH levels as low as 6.5 mIU/mL. So there’s a lot of wiggle room!
LH surges last between 24 to 36 hours on average. But surge patterns vary widely from person to person and cycle to cycle. Some surges are rapid and over within a day. Others are gradual and stretch up to six days. To learn more about LH surge types, check out this article.
It depends on the person and where you’re at in your cycle. Like LH surges, LH levels vary a ton. Here’s an LH chart levels chart that should help:
Time frame | LH level |
Follicular phase | 1.68 – 15.0 IU/mL |
LH surge | 21.9 – 56.6 IU/mL |
Luteal phase | 0.61 – 16.3 IU/mL |
Menopause | 14.2 – 52.3 IU/mL |
Low LH levels can lead to fertility issues. Irregular menstrual cycles or skipped periods may also happen. Typically, when LH is low, FSH is low too.
High LH levels can be a sign of polycystic ovary syndrome. Women with PCOS often have irregular periods and problems with ovulation. High LH is also common in perimenopause or menopause. This can lead to symptoms like hot sweats, vaginal dryness, sleep issues, or moodiness.
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- Physiology, Luteinizing Hormone – StatPearls – NCBI Bookshelf
- Physiology, Thyroid Stimulating Hormone
- Urinary Luteinizing Hormone Tests: Which Concentration Threshold Best Predicts Ovulation? – PMC
- (PDF) Development of the first urinary reproductive hormone ranges referenced to independently determined ovulation day
- Relationships between the luteinizing hormone surge and other characteristics of the menstrual cycle in normally ovulating women – Fertility and Sterility
- Relationships between the luteinizing hormone surge and other characteristics of the menstrual cycle in normally ovulating women – Fertility and Sterility
- Ovulation Prevalence in Women with Spontaneous Normal-Length Menstrual Cycles – A Population-Based Cohort from HUNT3, Norway
- Detection of ovulation, a review of currently available methods – PMC
- Luteinizing Hormone Deficiency – StatPearls – NCBI Bookshelf
