Tracking your LH surge is helpful in predicting ovulation, but what happens once you’re pregnant? Does LH stay around, or does it disappear completely? Get an OBGYN’s insight.


By Dr. Kenosha Gleaton

Tracking the LH surge is a useful way to detect ovulation during your fertility window to maximize efforts when trying to conceive. However, occasionally ovulation tests can give false positive results in conditions including PCOS (polycystic ovarian syndrome) and early pregnancy. Why does this happen?

Learn how the luteinizing hormone surges, ovulation, and your fertile period relate when TTC.

LH, LH surges, and fertile windows

LH stands for luteinizing hormone which is a hormone released by your brain that tells your ovaries to release a mature egg. A surge in the LH level actually triggers the release of the egg. This process of egg release, known as ovulation which takes place between the follicular phase and luteal phase of the menstrual cycle, is significant because it represents a finite window when a woman can conceive.

When LH surges in the blood, the increased levels are excreted in urine and can be detected in urine tests referred to as ovulation tests kits or ovulation predictor kits (OPKs). If the test result is positive, it indicates that ovulation will occur in the next 24 to 48 hours. This represents the fertile window and is the ideal time to have intercourse if trying to conceive.

Why is the fertile window the best time to try to conceive?

Ovulation timing is critical when planning on getting pregnant because of the short fertile window. Once released from the ovary, the mature egg only survives for 24 hours. Thus, timing is literally everything when TTC─and even when not. The fertile window represents the time frame of five days prior to and the day of ovulation. Approximately 12-24 hours after ovulation, a woman is no longer able to conceive during that menstrual cycle.

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Does LH surge stay high once you’re pregnant? Will you have LH at all?

No, a surge in LH level does not remain elevated once pregnant. In fact, LH levels are really low during pregnancy (< 1.5 IU/L), and thus not active on end organs and tissues.

Can pregnancy falsely indicate an LH surge?

There are several conditions that can make detection of the LH surge difficult. Pregnancy is one such condition that can falsely indicate an LH surge because pregnancy hormone levels, known as hCG levels, are similar in structure to LH, and they bind to a common receptor. The most notable difference between the two is that hCG has a circulating half-life that is approximately 80-fold longer than that of LH. One study refers to hCG as a “super LH produced in pregnancy,” with 80 times the biological activity of LH.

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Can you use an ovulation test kit if you have PCOS?

While using an ovulation predictor kit to plan your peak fertility is helpful when TTC, there are certain conditions, like PCOS, that affect its accuracy. An ovulation predictor kit measures the levels of LH to predict ovulation. However, with PCOS, hormone levels maymake it difficult to accurately predict when ovulation will be or provide a false positive.

Can I use ovulation tests to test for pregnancy?

We do not recommend using ovulation tests to determine if you’re pregnant for two reasons:

  • Ovulation tests are not as sensitive as some early pregnancy tests (25 mIU/mL vs 10 mIU/mL).
  • It’s nearly impossible to determine if a positive ovulation test is from LH or hCG.

Therefore, you run the risk of a false negative if it’s too early and a false positive if it’s picking up LH. If you think you might be pregnant, the best and most accurate way to confirm is to use an early detection pregnancy test.

Empower yourself with knowledge—and proper tests

Understanding the phases of the menstrual cycle and identifying the fertile window can be empowering when trying to get pregnant, especially when the pre-pregnancy journey seems longer than expected. Tracking your ovulation timing can increase your chances of getting pregnant by telling you the best time to have sex. Ovulation tests take out the guesswork so you can get down to business. But if you think you might be pregnant, the best and most accurate way to confirm is to use an early detection pregnancy test.