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Getting Pregnant

How Long Does the LH Surge Last for You?

ovulation in process

When you first started thinking about having a baby, the phrase “LH surge” probably didn’t cross your mind. But if you’re trying to get pregnant, you’ve probably developed a sudden new interest in monitoring the level of luteinizing hormone (LH) in your urine.

What is luteinizing hormone?

LH is a hormone produced by your pituitary gland that triggers ovulation.

Throughout most of the month, your LH levels are low. But once the egg in your ovaries reaches a certain stage of development, LH levels increase rapidly. This rapid increase is called the LH surge.

Ovulation usually occurs 24 – 36 hours after the LH surge first begins. But keep in mind that having an LH surge does not guarantee that you will ovulate, and the exact timing from LH surge to ovulation can vary from woman to woman (more on that below).

Why is LH important for getting pregnant?

Since levels of LH spike about 24 hours before ovulation, tracking your LH surge can help you determine when your chances for pregnancy are highest.

The fertile window is 6 days: the 5 days leading up to ovulation, and the day of ovulation itself. If you are trying to get pregnant, you must have sex during that 6-day fertile window.

Your chances of getting pregnant peak during the 2 – 3 days before ovulation. Since LH surges about 1 day before ovulation, monitoring your LH levels can help you identify some of the most fertile days of your cycle.

Keep in mind, however, that the LH surge occurs toward the end of your fertile window. If you wait for your LH surge to start having sex, you could be missing out on some of the best days of your cycle to conceive.

How do you detect your LH surge?

You can detect levels of LH in your urine by using ovulation tests (also called LH tests). These tests read a positive result when the level of LH in your urine is above a certain threshold.

Since the LH surge typically occurs 24 hours before ovulation, you can use these tests to predict when you will ovulate.

If you start taking LH tests several days before you expect to ovulate, the idea is that you will “catch” your surge with enough time to have sex during your peak level of fertility. This is why it’s important to know when to take an ovulation test.

How long do you ovulate after the LH surge?

On average, women ovulate 24 hours after the onset of the LH surge. But this number varies considerably from woman to woman. In fact, this variability is so significant that for some women, LH tests might not be the best way to estimate peak fertility.

A 2018 paper called into question the practice of using LH tests to predict peak fertility. The paper argued that the duration of the LH surge varies substantially both within and between women. Additionally, ovulation can occur at the beginning of, during, or after the LH surge.

This means that a single positive LH test doesn’t tell you that you are going to ovulate in 24 hours. Depending on the length of your personal LH surge, as well as how long it takes your ovaries to respond to the LH signal, a positive LH test might mean that you will ovulate soon, are ovulating right now, or even that you ovulated yesterday and are no longer fertile.

How long after the LH surge are you fertile?

On average, ovulation occurs 24 hours after the first positive ovulation test. That means that you could have several days of positive tests in a row, but already ovulate after the first day.

What’s more, by the time you get a positive ovulation test, your most fertile days may already be behind you. That’s because your best chances to get pregnant are the three days before ovulation. The LH surge only occurs about 24 hours before ovulation.

And not all women ovulate 24 hours after the LH surge. Up to 70 percent of women have cycles that don’t match up to clinical guidelines. Some women ovulate sooner than that, and others ovulate later.

Some women continue to test positive for three days after a positive ovulation test. If you’re one of these women, a positive ovulation test doesn’t necessarily mean that you are fertile at all.

How long does the LH surge last?

The length of the LH surge is highly variable from woman to woman. And the actual length of the LH surge does not determine your fertile window.

Think of the LH surge as the kick-start to ovulation: once the LH surge begins, it doesn’t matter how long it lasts.

A study in the journal Fertility and Sterility looked at how long the LH surge lasts in normally ovulating women. The image below represents what different LH patterns would look like on daily LH tests from cycle day 11 through cycle day 21 according to the results of the study:

As you can see from this chart, some LH surges are long, and others are short. If you happen to have a long LH surge, it doesn’t mean you are more fertile—it simply means you will get a few days of positive LH tests before you actually ovulate.

It’s best to think of levels of LH in your body as a curve that changes throughout your cycle. In the typical cycle, LH starts out low, then rapidly rises and peaks a day or two before ovulation, then falls back down right after ovulation. But just as not every woman has a textbook 28-day cycle, not every woman has exactly the same LH curve.

What are the symptoms of the LH surge?

The LH surge itself does not have any physical symptoms. But there are signs and symptoms of ovulation that you can track in order to determine when you ovulate. Most signs of ovulation are driven by the hormone estrogen.

Estrogen levels begin to rise roughly 5 days before ovulation. Rising estrogen levels cause your vaginal discharge (also known as cervical mucus) to increase and become more slippery. This is one of the best indicators that ovulation is approaching.

Once estrogen reaches a certain threshold, this triggers the release of LH. This means that you should notice increased fertile vaginal discharge around the time of the LH surge. But the discharge is a symptom of increased estrogen levels, not LH.

Do you definitely ovulate after LH surge?

Not necessarily. Think of the LH surge as a sign that your body is preparing for ovulation. Ovulation usually will follow the LH surge, but having an LH surge is not a guarantee that ovulation will occur.

To confirm that ovulation occurred, you would need to observe an increase in basal body temperature, or have your progesterone levels checked by your doctor.

There are several reasons why you would have an LH surge but not ovulate:

  • PCOS: This (and other hormonal conditions) can cause elevated LH levels throughout the menstrual cycle
  • Luteinized unruptured follicle (LUF): even though hormone levels leading up to ovulation are normal, the follicle doesn’t rupture, so the egg is never released.

Between 6 – 25 percent of women with infertility have LUF, and it’s one possible cause of unexplained infertility. It can also occasionally happen to women with otherwise normal cycles.

In normal menstrual cycles, the ruptured follicle becomes a corpus luteum, which releases progesterone and stimulates the lining of the uterus to build up. But with LUF, even though the follicle never ruptures, it still releases progesterone. From the outside, your cycle will look completely normal: you’ll still get a regular period each month, and you’ll still get positive results with the temperature method or ovulation sticks. In fact, the only way to detect LUF is via ultrasound.

Often, there is no apparent cause for LUF. But it is known that long term use of anti-inflammatory drugs can prevent the follicle from bursting, sometimes leading to LUF. If you’re taking anti-inflammatory drugs for chronic conditions like autoimmune diseases, arthritis, or endometriosis you may want to talk to your doctor about possible impacts on your fertility.

What are normal LH levels?

Most of the time, blood concentration of LH is between 5 – 20 mIU/mL. Roughly 24 – 36 hours before ovulation, LH levels begin to surge to a peak of 25 – 40 mIU/ml.

Since normal LH levels vary between women, another way of defining the LH surge is the first day of your cycle when LH concentration is three times the concentration of the six previous days.


View sources

Relationships between the luteinizing hormone surge and other characteristics of the menstrual cycle in normally ovulating women

Timing of Sexual Intercourse in Relation to Ovulation — Effects on the Probability of Conception, Survival of the Pregnancy, and Sex of the Baby

Timing is crucial: Some critical thoughts on using LH tests to determine women's current fertility

Chronological aspects of ultrasonic, hormonal, and other indirect indices of ovulation

Lindsay Meisel

Lindsay Meisel is the Head of Content at Ava. She has over a decade of experience writing about science, technology, and health, with a focus on women's health and the menstrual cycle. Her work has been featured on The Fertility Hour, The Birth Hour, The Breakthrough Journal, and The Rumpus.

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