What does the LH surge mean for pregnancy?

When the body’s levels of luteinizing hormone (LH) rise, it triggers the start of ovulation, and the most fertile period of the menstrual cycle occurs.

Tracking the surge in luteinizing hormone levels can help people to plan intercourse and increase the chances of becoming pregnant.

Understanding what LH is, when levels of the hormone rise, and the relationship between this increase and fertility can be important for women trying to get pregnant.

There are several ways to track monthly LH surges. In this article, we describe methods of tracking, how long surges last, and how to use them to increase the odds of pregnancy.

What does a surge in LH mean?

Man and woman discussing a menstrual cycle
The period of fertility is short, so it is important to keep track of it.

The LH surge signals that ovulation is about to start. Ovulation is the medical term for an ovary releasing a mature egg.

A gland in the brain, called the anterior pituitary gland, produces LH.

Levels of LH are low for most of the monthly menstrual cycle. However, around the middle of the cycle, when the developing egg reaches a certain size, LH levels surge to become very high.

A woman is most fertile around this time. People refer to this interval as the fertile window or fertile period.

If there are no complications affecting fertility, having sex several times within the fertile period may be enough to conceive.

How long does the LH surge last?

The LH surge begins around 36 hours before ovulation. Once the egg is released, it survives for about 24 hours, after which time the fertile window is over.

Because the period of fertility is so short, it is important to keep track of it when trying to conceive, and noting the timing of the LH surge can help.

When to test LH levels

For people trying to conceive, the best time to have unprotected sex is during the LH surge.

Ovulation predictor kits (OPKs) contain at-home tests that measure LH levels in the urine.

It is best to start testing levels when the fertile window is drawing near, or a handful of days before ovulation.

Most people ovulate between 7 and 19 days before their next period begins.

Many people ovulate on day 14, but this can vary, depending on the length of a person’s cycle. People with shorter cycles should test earlier in the range of likely days.

Best ways to test LH levels

woman having a blood test
One of the best ways to test for the LH surge is to get a blood test.

There are multiple markers of ovulation, including:

  • LH levels in the urine
  • the number of days since the last menstrual period
  • the consistency of the cervical mucus

The best ways to test for the LH surge are:

  • getting a blood test from a doctor
  • using a home test in an OPK

A person can buy an OPK without a prescription, from drug stores or online. Many brands are available.

A positive result means that a person has a high amount of LH in their system. LH levels drop after ovulation, so the tests only show positive results during fertile periods.

Because each kit is different, it is important to follow the instructions carefully. All tests are relatively simple to use.

However, there are a few disadvantages, and OPKs may not be the right choice for everyone.

For example:

  • If a person has irregular cycles, testing can be difficult, expensive, frustrating, and unreliable.
  • Women with polycystic ovary syndrome (PCOS) may experience persistently high LH levels, and tests may show positive results throughout their cycles.
  • Women approaching menopause may also have elevated LH levels, which makes test results unreliable.
  • Testing at the right time is essential. If a person tests too late in their cycle, they will miss the LH surge and have to wait until the next month.
  • If it takes a long time to conceive, buying multiple OPKs can get expensive.

If OPKs are unlikely to be effective, a person can ask their doctor for a blood test. It may take a few tests to identify the fertile period and to pinpoint the time of ovulation.

A doctor can also identify the fertile period by examining the ovaries on a transvaginal ultrasound scan.


For women trying to get pregnant, it is important to track the window of fertility and the LH surge.

A person can figure out the timing of the LH surge with an OPK or by taking a blood test. A doctor can help to decide which method of tracking will be most effective.

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