Understanding Your LH Surge & How It Impacts Pregnancy (+ LH Surge Chart)

by Aug 26, 2021

When it comes to your monthly menstrual cycle, a delicate dance of hormones are at play that can tell you many things about your health.  But when it comes to fertility, some are more important to keep track of than others.

When you are trying to conceive, luteinizing hormone (LH), and how it changes over the month is an important factor to consider.  You can’t get pregnant without ovulation and you need your LH to reach peak levels to trigger that process.  Knowing when your LH surge happens can be crucial information for those trying to conceive and make the most of their fertile window.  Read on to learn what an LH surge is and what it means for anyone TTC.

What is luteinizing hormone?

Luteinizing hormone is an important pregnancy hormone that essentially controls the functions of the ovaries.  It directly impacts the reproductive system and is a major marker for fertility issues.  Although its job changes over the course of your cycle, stimulating the ovaries to produce estrogen in the first half then the corpus luteum to produce progesterone, LH plays a key role in predicting ovulation and regulating your menstrual cycle.

What is an LH surge?

Normally, LH levels remain fairly steady throughout the menstrual cycle but just before ovulation those levels surge dramatically.  This surge in LH is what triggers the release of an egg from the dominant follicle typically 24-36 hours later, enabling ovulation.  An LH surge does not always guarantee that a successful ovulation will occur, but tracking this hormone can still give you vital information about your fertile window.

LH surge symptoms

Although symptoms that are associated with an LH surge won’t occur in everyone, there are some physical changes that can help you identify when one is happening.  For instance, some women may experience slight twinges or ovarian pain before or during ovulation known as mittelschmerz.  You may also notice slight spotting that occurs around ovulation.  Although it’s different for everyone, this would be very light bleeding that occurs outside of your regular menstrual period.

Other physical symptoms you might experience include changes in cervical mucus and in your saliva.  Since both are triggered by surging hormone levels, you may notice changes in the consistency of these fluids.  Cervical mucus becomes more slippery and increases in volume and you may notice increased discharge with transparent mucus similar to the consistency of egg whites.  Changes to the consistency of saliva may cause patterns to form in dried saliva, but this symptom is less noticeable since eating, drinking, or brushing your teeth may mask it.

The most obvious and reliable symptom of an LH surge is to measure the changes in your hormones directly.  This requires more work, but offers the most effective method.  A tracking device like Mira Plus Starter Kit can help you monitor your personal LH surge and fertility hormone patterns for a more precise measurement of your fertility window.

When does the lh surge happen?

In women with regular cycles, LH peaks between cycle days 12 to 16 and may vary from cycle to cycle.  In women with shorter or longer cycles, those days could change depending on their cycle length.


Although the general narrative around LH surges is that there is one surge before ovulation, different patterns have been noted and there is some variability in what LH surges look like around ovulation.  Some women experience patterns that show a short surge, two surges, or even a plateau in levels but the single LH peak is the most commonly observed of all patterns.

How long does an lh surge last?

In theory, and for a perfectly “regular” cycle, the LH surge lasts approximately 24-36 hours and occurs approximately 10-12 hours before ovulation.  But in reality, the duration of the LH surge is different for each woman, and may even differ from cycle to cycle.  If you are trying to conceive, noting the length of your LH surge in relation to your ovulation day is usually best.

Since getting the timing right is so crucial to conception, if you can pinpoint when your LH surge happens, you have a better chance of timing intercourse for baby-making success.  Tracking your hormone levels can help you detect when your LH surge is approaching or give insight into your own unique surge pattern with an LH surge chart.

LH surge and ovulation

The LH surge sends a signal from the brain to the ovary that an egg is ready to be released from the ovary.  When the follicle sees this hormone increase, it completes maturation of the egg and allows it to be released from the ovary (aka ovulation).

This surge in LH is what actually triggers ovulation and the egg is usually released from the follicle after LH peaks.  Your LH surge isn’t ovulation itself but is the signal that ovulation is about to start.  No LH surge means no ovulation.

How long after an lh surge do you ovulate?

The time from lh surge to ovulation can vary from woman to woman.  In healthy women with normal cycles, ovulation usually takes place 24-36 hours after the LH surge.  Ovulation time varies though from both woman to woman and cycle to cycle.

Tracking and logging the details of your menstrual cycle can help predict ovulation but any factors that influence your hormones can influence ovulation and it doesn’t necessarily happen like clockwork.  Because your LH surge indicates that you are in your fertile window it can be important to note its timing, especially if you are trying to conceive.

When should you have sex after an LH surge?

Your fertile window is the short time surrounding ovulation when unprotected intercourse is most likely to lead to a pregnancy.  It is a combination of both how long sperm cells can survive inside a woman and how long her egg survives after ovulation.

Because a woman’s egg can only live up to 24 hours after ovulation and a man’s sperm can live for up to five days in the female reproductive tract, knowing this window of time can be of the utmost importance for anyone TTC.

We know that ovulation generally occurs a day or two after the LH surge which means that if you are trying to conceive, you should be having sex in the days immediately following your LH surge.  Optimizing this information via home tracking and monitoring can help you time your intercourse during your fertile window.

How do you detect an LH surge?

There are a number of methods available to detect an LH surge, each with their own benefits and drawbacks:

  • Ovulation predictor kits (OPKs)
  • Tracking the physical signs of ovulation
  • Tracking your cycle
  • Blood test or urine.

Many women use ovulation predictor kits, similar to home pregnancy tests, to detect their LH surge at home.  These kits measure hormone levels in your urine and a positive result will indicate the presence of a high amount of LH.  Since the LH surge triggers ovulation, a positive ovulation test should mean you are going to ovulate within the next 24-36 hours.

Each test is different and standard tests only give a positive or negative result, giving you a snapshot of your fertility at that time rather than the bigger picture.  The Mira Fertility Tracker is able to display laboratory-grade results of your actual hormone concentration with 99% accuracy.


The most accurate method of measuring your LH surge is by measuring the amount of LH in your bloodstream.  You will need multiple tests to track the rise and fall of LH levels this way and your doctor or fertility specialist will help interpret the results.

The benefits of testing this way include precise results and the help of your medical team.  However, this method is more time consuming as it can’t be done at home, and the costs associated with the time and length of procedures make it less than ideal.

At home

At home testing can be done via saliva or urine.  The advantage to home testing (besides convenience) is that it can be done as many times as you want.  As long as you are testing regularly, you can use home tests to accurately predict your LH surge as well as your fertile window.

Ovulation predictor kits are a common way to detect your LH surge and the tests will only show positive results during your fertile period.  A positive result indicates a high amount of LH in your urine or that you are in your surge.

Although the tests are easy to use, they aren’t for everyone and women with cycle irregularities or ovulatory issues may find the testing difficult, expensive, and unreliable.  This is especially true for women approaching menopause or those with polycystic ovarian syndrome (PCOS) who may have higher LH levels.

Fertility tracking devices like Mira can measure your LH levels (as well as other hormones) over time.  Mira measures the actual hormone concentration in your urine allowing you to learn your unique levels and how they relate to ovulation.  With 99% accuracy for predicting ovulation, this allows you to make the best use of your fertile window.

Using this system, you’re able to track personalized information on par with what you would get at a doctor’s office without the hassle of going to an appointment.  Mira can be especially helpful if your levels deviate from population averages or your cycle is irregular with a companion app that uses smart learning to track your cycle over time.  This information can also be shared with your doctor as you navigate your TTC journey.

LH surge chart

✔️ Medically Reviewed by Katerina Shkodzik, M.D., OB-GYN

Dr. Katerina Shkodzik is a certified OB-GYN with a special focus on reproductive endocrinology and infertility issues. She has been practising since 2015.

Dr. Shkodzik completed her residency program in the Department of OB/GYN at the Belarusian State Medical University and fellowship program in the Department of Gynecological Surgery at the Medical University of Bialystok, Poland.

Dr. Shkodzik is extensively involved in digital health projects providing her medical expertise and integrating of cutting edge technologies in medical science and clinical practice since 2018.

Dr. Shkodzik has participated in several studies focused on PCOS, endometriosis, menstrual cycle characteristics and their abnormalities based on big data of digital health in collaboration with leading universities.

She believes that paying special attention to women's health is a crucial step to improving the world we live in.

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