This article was last updated April 27, 2021.
If you’re someone looking to track when you ovulate, chances are you’ve heard of luteinizing hormone (LH). Of all the cycle-tracking methods out there, LH testing ranks high on our list of favorites because of its clear role in inducing and predicting ovulation — a mid-cycle surge in LH is absolutely necessary for ovulation to occur. And if you’re trying to conceive, testing for LH surges can help you time sex or insemination around your fertile window (the five days leading up to and the day of ovulation) — when you have the highest chances of getting pregnant.
But just because mid-cycle surges in LH are necessary for ovulation doesn’t mean LH levels look the same across all people and all cycles. In fact, LH levels and LH patterns across the cycle are far from being one-size-fits-all.
In this post, we’ll highlight findings from a few of our favorite studies that lead us to question what “normal” really means in the context of LH across the cycle. More specifically, we’ll take a look at what science has to say about these two important questions:
- What is a “normal” LH level on different days of the cycle?
- What’s considered a “normal” pattern of LH around ovulation?
The main takeaway: There is a wide range of what's considered “normal” for urinary LH
- One large study showed that the median LH on the day before ovulation was about 44.6 mIU/mL, but that LH could be as high as 101, or as low as 6.5. Yep — some women had an LH of 6.5 the day before ovulation!
- Values considerably below the average lower limits and above the average upper limits might be indicative of an underlying condition that may impact ovulation. If you track your LH and discover this, it's worth bringing up to your doctor.
- Another study shows that the average LH surge was characterized by a 7.7-fold increase in LH from baseline — but LH surges ranged from 2.5-fold to 14.8-fold increases from baseline.
- According to a few studies (here, here, and here), there are many different LH surge patterns: 42%-48% of cycles have a short LH surge before ovulation; 33%-44% of cycles have two LH surges (an initial big rise, small drop, then a second rise in LH); and 11%-15% of cycles have a "plateau" pattern (when levels of LH remain high after an initial surge).
What is LH and why is it important?
Hormone levels shift across your menstrual cycle to gear your body up for ovulation — including luteinizing hormone (LH), which is produced by the pituitary gland:
- At the onset of your menstrual period, your body has low levels of important reproductive hormones, such as LH, follicle-stimulating hormone (FSH), and the estrogen estradiol (E2).
- In the two-ish weeks after your period starts, the dominant follicle develops. It contains the egg that will eventually get released — and the follicle produces more and more E2 as it develops.
- Around 24-48 hours before the egg is released, there are large hormone surges of LH and FSH which will trigger the follicle to release an egg (read: ovulation).
LH surges are necessary for ovulation: If there’s an LH surge, chances are pretty high that ovulation is coming. If there’s sperm hanging around once the egg has been released into the fallopian tubes, conception is possible (though not guaranteed).
Are there any physical symptoms that accompany an LH surge?
No, there aren't any "symptoms" that come along with an LH surge specifically. But two bodily changes can clue you in to when ovulation might come for you:
Cervical mucus changes
Your body produces stretchy cervical mucus, similar to an egg white in consistency, in the days before ovulation (day 14 if you have a 28-day cycle). After ovulation, you’ll see less mucus. You can track changes in your cervical mucus in the following ways:
- Wiping your vaginal opening with toilet paper before you pee and inspecting what’s left on the toilet paper.
- Noting mucus appearance, color, and texture on your underwear.
- Inserting fingers into your vagina to see mucus color and feel its consistency. If you then put your fingers into a glass of water and the substance either stays on your fingers or sinks to the bottom of the glass, then it’s definitely cervical mucus — as opposed to vaginal fluids (made up of water and microorganisms) that help to keep the vagina clean.
Basal body temperature increase
Your body’s at-rest temperature, called your basal body temperature (BBT), may slightly increase during ovulation and remain at a higher temperature until your cycle ends. But because there are many factors that influence your body temperature beyond your cycle (e.g., fever, illness, stress, alcohol, hormonal birth control, lack of sleep, and jet lag), it’s an unreliable way to get a read on ovulation.
How can you detect an LH surge?
Aside from an ultrasound that looks at your ovaries, your LH level is the most direct way to predict ovulation because the hormone is biologically implicated in the process of ovulation.
Ovulation tests, or ovulation predictor kits (OPKs), are urine tests that measure LH to help you pinpoint when your level is surging. Many ovulation tests are threshold-based, meaning they use a predetermined urine LH threshold to give you a test result (positive or negative) to help you predict whether or not you’ll ovulate soon.
(Note: The Modern Fertility Ovulation Test is not threshold-based — our test kits are semi-quantitative, which means you’ll be able to see your LH change daily and track low, high, or peak levels.)
What is a "normal" LH level on different days of the cycle?
The fact that many manufacturers of ovulation test kits use a single threshold for all uterus owners might lead you to think that there are thresholds that predict ovulation for everyone, and/or that there is a well-defined, narrow window of what “normal” LH looks like before ovulation and across different cycle days.
Just like there is a range of what’s considered “normal” for the Modern Fertility Hormone Test (we call this the reference range), we can use data from a large enough pool of people to figure out what typical levels of urinary LH are across different days of the cycle:
- According to one of the largest studies that analyzed LH daily and used ultrasound to confirm the timing of ovulation, there is quite the range in what LH values we can expect across different cycle days, and this range is the largest 24 hours before ovulation.
- In the graphic below, we show median LH (the black dots), and the distribution of reported LH values, minus the upper 10% and lower 10%. This is also called an 80% reference range — all the values that constitute the middle 80% of the distribution of LH. (Put in other words: What an 80% reference range tells us is that 10% of values fall below the bottom of the range’s lower limit, and 10% of values fall above the range’s upper limit.)
- While some studies or labs choose to report 80%, 90%, or 95% reference ranges, the study these data come from chose to use an 80% reference range.
Let’s first take a close look at the day before ovulation
In this sample, though the median LH on the day before ovulation was about 44.6 mIU/mL, it wasn’t abnormal for LH to be as high as 101, or as low as 6.5. Another way of putting it? Women with LH values that were 1/7th of the median to values that were more than double the median were all considered within the bounds of “normal.”
While not as pronounced, there was significant variation in LH on other cycle days, too:
- At 10 days before ovulation, for example, 80% of women had values anywhere between 2.8 and 11.9 mIU/mL.
- The general takeaway from this data is that there’s a big range of LH values that can be considered typical across all cycle days. This is important to keep in mind if you find yourself asking: “Is my LH today normal?”
- That being said, values considerably below these lower limits and above these upper limits might be indicative of an underlying condition that may impact ovulation, and should be presented to and discussed with a physician.
- However, having LH values within these limits doesn’t 100% exclude the possibility of an underlying condition — if you consistently have “normal” LH values, but have other reasons to suspect you’re not ovulating regularly, you should discuss this with a physician as well.
What is a "normal" pattern of LH around ovulation?
Visuals and text from medical textbooks indicate that there is a single, large pre-ovulatory LH surge that lasts for about 24 hours. This pattern makes two assumptions about LH around ovulation:
- The LH increase is always super dramatic.
- There is a single, transient LH peak.
Let’s break those down one by one to see what science says is “normal” for each.
Variability in the percent that LH increases around ovulation
When talking about LH during ovulation, some sources are often vague about exactly how much of an increase in LH is characteristic of an LH surge and peak. If LH doubles, is that considered a surge? What if it quadruples? What if it increases 20-fold? For those using semi-quantitative LH test kits (i.e., tests that actually tell you what your LH is, rather than just telling you whether you’re above or below a predetermined threshold value) to track ovulation, this is an important question.
At what point does an increase signal that ovulation is likely around the corner, versus just being “normal,” daily variability in LH production? Because threshold-based tests (i.e., tests that compare your LH to a predetermined baseline to make inferences about ovulation) do not rely on patterns over time, this question is not so relevant to their users. We’ll again turn to one of our favorite studies that examines the variability in how much LH increases around ovulation, when ovulation is confirmed by ultrasound.
- According to this study of 43 premenopausal women, on average, the LH surge was characterized by a 7.7-fold increase in LH from baseline. (Earlier studies had pinned this number at being slightly lower — closer to a 4-fold or 6-fold increase — but we’ll put more trust in data that is more recent and based on a larger sample size.)
- But here’s the important thing: In confirmed ovulatory cycles in this study, LH increases ranged from 2.5-fold to 14.8-fold.
- Other studies have since replicated this effect, meaning we can be confident that there truly is a wide range in the amount that LH has to increase to induce ovulation across women.
Now, let’s take a made-up example to really drive home what this variability in percent increases in LH can look like. Let’s say there are two people who have baseline LH values of around 6 mIU/mL from the beginning of their cycles to the few days before ovulation:
- One person's peak LH value would be around 15.
- For the other person, their peak LH value would be around 89.
- Both of these people would ovulate.
Variability in what LH surges look like around ovulation
Because the general narrative says the menstrual cycle is characterized by one quick LH surge before ovulation, you might be surprised to learn that according to some studies, less than half of women have LH patterns that look like that (though it is the most commonly observed out of all the noted patterns).
Of studies that have characterized what patterns of LH might look like for different people, there are three recent ones (here, here, and here) that stand out as being particularly strong, and all three have converged on around the same estimates for what percent of women display which patterns:
- Between 42% and 48% of cycles follow the “short surge” pattern. This is the one we’re most familiar with, because this is the pattern talked about in medical textbooks and in most descriptions of the menstrual cycle.
- Between 33% and 44% of cycles follow the “two surges” pattern, which — yup, you guessed it — is characterized by an initial big rise, a small drop, and then a second rise in LH.
- Between 11% and 15% of cycles are characterized by the “plateau” pattern, which is when LH levels remain high after an initial surge (rather than quickly falling back down).
There are other patterns as well, including multiple surges (think the two surges pattern, and then some), though they are less frequent.
While some studies suggest that the pattern of LH around ovulation should look the same within an individual from cycle to cycle, others report the opposite (i.e., that LH surge characteristics differ across cycles). Our take? If you have a short surge one cycle and a plateau next, it isn’t something to lose sleep over.
Two LH surges do not mean you ovulate twice (and sustained LH levels don’t mean you ovulate for longer)
Now, we know we said earlier that an LH surge indicates that ovulation is likely coming up soon, so it may be tempting to think that two LH peaks means you ovulate twice, or that a sustained high level of LH means you’re ovulating for longer. Both of these are not true.
For the purposes of ovulation tracking, the main thing to keep an eye out for is that initial LH surge, because it’s that initial surge that’s predictive of ovulation and peak fertility.
- If you fall in the “short surge” camp, you can be fairly confident that if you detect high LH (whatever “high” means for you), ovulation is around the corner.
- But for those who fall in the “two surge” or “plateau” camp, a high LH doesn’t always indicate your first LH surge — it could be indicative of a second LH surge, or of sustained high LH after a first surge.
When should you start testing for an LH surge?
The exact guidelines for how you should use ovulation tests depend on how regular and long your cycles are. The “textbook” 28-day cycle sees ovulation occurring on day 14. In these cases, ovulation test manufacturers recommend starting to test a couple of days before the anticipated day of ovulation.
Chances are, though, that you don’t have a “textbook” cycle — simply because most people don’t. Cycles are commonly shorter or longer than 28 days, and it isn’t always the case that ovulation happens exactly in the middle of the cycle. If this sounds like you, the conservative approach would be to start testing a couple of days after your period ends and to continue testing until you get indications that ovulation is coming up:
- For our Ovulation Test, we recommend you start testing 19 days before the start of your period. To figure out when that is, you’ll need to determine your average cycle length and subtract 19 days from that number — the number you end up with is the cycle day you should start testing. If you have a 28-day cycle, you’d begin taking ovulation tests starting on cycle day 9.
- Regardless of when in your cycle you start using ovulation tests, the way you use them should be similar and consistent. Because LH peaks are very transient (though again, this applies to the “textbook” pattern of cycle-based hormonal changes), ovulation test manufacturers often recommend testing once every 12 hours around the time of anticipated ovulation to make sure that the peak isn’t missed.
- It's also important to test at approximately the same time of day each day and to avoid testing after drinking excessive fluids (because your urine will be too diluted).
Bottom line: "Normal" has more than just one look
Tracking your LH is one of the most powerful at-home tools science has given us to predict ovulation and our fertile window to increase our chances of getting pregnant — but it’s easy for the worries of “is my LH normal?” to put a major damper on the LH-tracking experience. By understanding that there’s a range of LH values considered “normal” on each cycle day and that the patterns of LH around ovulation can take different forms, you’ll be better armed to embrace your unique pattern of LH, and also have a better understanding of when something might be off.
The Modern Fertility Ovulation Test helps you pinpoint your luteinizing hormone (LH) levels to predict your 2 most fertile days. With our test, you’ll get more insight than just a positive result or negative result. Here’s some of what you can learn about your LH levels:
- You’ll be able to see your LH change daily and track low, high, or peak levels.
- You can use it to see what your LH values are each day, how much they surge mid-cycle, and what your overall LH pattern looks like around ovulation.
- When LH meets antibodies on the test strip, the test line darkens — the darker the line, the more LH there is in your urine.
- Unlike other ovulation tests, you'll be able to match the shade of your test line to the corresponding LH level (kind of like those pH strips you played with in middle school).
- Or if you’re using our free app, you can automatically scan and log your tests with your camera, so you always know where you are in your cycle.
However you choose to track your ovulation — and whether you’re trying to increase your chances of getting pregnant or just learning more about your body’s hormonal patterns — we’re here to demystify your hormones and help you take charge of your reproductive health.
This article was reviewed by Dr. Jennifer Conti, MD, MS, MSc. Dr. Conti is an OB-GYN and serves as an adjunct clinical assistant professor at Stanford University School of Medicine.