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Around the midpoint of your cycle, levels of luteinizing hormone (LH) surge. This marks the start of your fertility window.

Luteinizing hormone and fertility

What if you learned there was a marker for your fertility? What if it could help shorten the time it takes to get pregnant?

For many women, the luteinizing hormone (LH) surge is that marker. Learning how to detect it can make baby-making easier. Here’s how.

What is luteinizing hormone?

LH is one of the hormones produced by the pituitary gland. Ordinarily, it’s secreted at very low levels throughout your menstrual cycle.

But once a developing egg follicle reaches a certain size — usually around the midpoint of your cycle — LH secretion surges to really high levels. This hormone surge is what triggers ovulation about 24 to 36 hours later.

Ovulation is the release of a mature egg from the ovary. It signals the beginning of your fertile period. After the egg is released, the empty follicle on the ovary is converted to a structure known as the corpus luteum. It then begins to secrete progesterone. Progesterone is a hormone needed to support a potential pregnancy.

If pregnancy doesn’t occur, the corpus luteum shrivels up, stopping the secretion of progesterone, and triggering the start of a menstrual period.

Why is the LH surge important?

Your LH surge is important because it initiates the beginning of ovulation and your fertile period. If you’re trying to get pregnant, this is the best time for you to begin having sex without a condom.

Once the egg is released, it’s only viable for about 24 hours. After that, your fertile window is over. This makes it very important to be able to identify this best time to conceive.

How to detect your LH surge

For many women, it’s easy to detect their LH surge using ovulation predictor kits (OPKs). These are readily available online and in most pharmacies.

These kits are similar to pregnancy tests because they measure hormone levels in your urine. Each kit is a little different in how they register a positive result, so make sure to check the instructions.

A positive result indicates the presence of a high amount of LH, or your LH surge. The amount of LH in your body will begin to decrease after ovulation, so you’ll only get a positive result during that crucial fertile period.

How often should you test for the LH surge?

It’s not necessary to test yourself every day (or multiple times a day) until you get a positive result. The tests can be expensive to use that frequently.

Ovulation usually occurs about 14 days before your period. Your LH surge occurs a day or two before that. So knowing how long your cycle is (from one period to the next) will help you figure out when to start testing.

For example, let’s say your cycle is 32 days between periods. Day one of the cycle is the first day of your period. Ovulation most likely occurs around day 18. You should get a positive result on an OPK a day or two before that, on day 16 or 17.

It’s a good idea to start testing every day (or every other day) in the morning a few days before that, around cycle day 13. This is to make sure that you catch the positive result, in case you have a shorter cycle that month.

Once you get a positive result, it’s time to start trying. Most experts recommend having sex two to three times over the next 24 to 48 hours.

Disadvantages of using an ovulation predictor kit

There are several disadvantages to using an OPK, including the following:

  • If you have irregular cycles, it can be difficult to figure out when to start testing. This can get expensive and frustrating.
  • Women with the condition polycystic ovary syndrome (PCOS) might not be able to use these tests. Some women with PCOS have persistently elevated levels of LH, which would lead to an OPK always displaying a positive result, regardless of where you are in your cycle.
  • Women approaching menopause may also have persistently elevated LH levels.
  • If you start testing too late into your cycle, you may miss the LH surge and won’t get a positive result that month.
  • Ovulation predictor kits can be expensive, and the cost can add up if you use several of them throughout a cycle, or through multiple cycles.

Other ways to detect your LH surge

If you have trouble using an OPK, you can ask your doctor to run some blood tests to help you pinpoint your ovulation. Usually, a gynecologist or reproductive endocrinologist (infertility specialist) can help you interpret the blood testing results.

You may need to have a few blood tests to determine your fertile period. Some doctors may also recommend a transvaginal ultrasound. This allows your doctor to look at your ovaries and see how the follicles are growing.

Next steps

Using an OPK can be a very effective way to help you become pregnant. But some women shouldn’t use these tests because they won’t work as well for them. If you get a consistently positive result, or you never get a positive one, visit your doctor to rule out other medical conditions.

If you’ve been using these kits and haven’t become pregnant after six months (if you’re over 35) to a year (if you’re under 35), make an appointment with your doctor. They can recommend a fertility specialist or treatment and testing options.


How long should a woman wait before seeing a fertility specialist if she’s trying to conceive?

Anonymous patient


There are three things necessary to get pregnant: an egg from the female (the product of ovulation), sperm from the male (the product of ejaculation), and an open passage from the uterus to the tubes for the two to meet. If the patient has been trying for at least six months (preferably 12) and there is no pregnancy, or if there appears to be an obvious problem with one or more of the three factors mentioned above, then she should see a fertility specialist.

Dr. Michael Weber

Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.
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