The principle behind ovulation tests is simple and intuitive: using a test strip or stick with a control line, you measure how much luteinizing hormone (LH) is present in your urine. LH is one of the key hormones that regulate your cycle. It triggers ovulation, supports the formation of the corpus luteum, and the corpus luteum in turn produces the hormone progesterone.
However, LH levels don’t just fluctuate throughout the menstrual cycle—they also vary significantly from woman to woman, and sometimes even within the same woman over the course of her fertile years. This becomes clear when looking at the numbers:
- In the first half of the cycle, the normal LH range in a healthy girl or young woman is 1.9 to 12.5 international units per liter (IU/L).
- Just before ovulation, during the so-called LH peak, levels rise sharply to 8.7 to 76.3 IU/L. This is why ovulation tests are often called “ovulation predictors.”
- After ovulation, LH levels drop again, falling to 0.5 to 16.9 IU/L in the second half of the cycle.
For women who take certain medications, have recently stopped hormonal contraception, are underweight, or are already in perimenopause, things can look very different. In these cases, LH tests may provide little to no reliable information. But more on that later.
