The Luteinizing Hormone (LH)
The luteinizing hormone (LH) plays different roles during the menstrual cycle. In the first two weeks of your cycle, LH stimulates the follicles in your ovaries to produce estrogen. In the middle of your cycle, LH rises sharply, triggering ovulation—the egg that has grown to 1 inch or 2.5 cm jumps out of the follicle and is released from the ovary.
Fig.: How LH triggers ovulation
The remnants of the egg are formed by the so-called corpus luteum (Latin for “yellow body”). In the third and fourth week of your cycle, LH takes on the task of stimulating the corpus luteum to build progesterone. If the egg released during ovulation is fertilized, progesterone is urgently needed to develop the embryo.
LH is, therefore, a real chameleon among the sex hormones; within a very short time, it takes on a wide variety of tasks without which female reproduction would not be possible.
Standard LH Range
The values that LH assumes during your cycle are just as varied as the tasks it performs. In the first two weeks of the cycle, it is low, with normal values between 1.9 and 12.5 U/l. One to two days before ovulation, it increases sharply, with normal concentrations in the range of 8.7 to 76.3 U/l. In the second half of the cycle, the LH level is 0.5 to 16.9 U/l. After menopause, the LH level increases and is in the standard range of 15.9 to 54.0 U/l.
Ovulation tests use LH’s soaring increase immediately before ovulation to predict whether you are about to ovulate. If you want to know when your most fertile days are, you can use urine strip tests for several days in a row. As soon as the LH level rises, two equally strong lines will appear on the strip, which usually means that ovulation will take place 24–48h later. The one to two days before ovulation are the most fertile time of your cycle.
When Is the LH Value Low?
If you use hormonal contraception or receive hormone replacement therapy, your LH value will decrease due to the medication. The same applies if you take GnRH agonists, which are used, for example, in the treatment of endometriosis, myomas, or hormone-sensitive tumors. However, there are also underlying pathological causes for a low LH value. These include
- Hyperprolactinemia (increased levels of prolactin in the blood)
- Olfacto-genital syndrome (Kallmann syndrome; a genetic disorder characterized by a general deficiency of sex hormones)
When Is the LH Value High?
Because the amount of LH fluctuates during your cycle, a high LH value should always be interpreted based on the cycle day. Drugs that boost LH include the hormones used in fertility medicine and chemotherapy drugs to treat cancer. Pathologic causes of excessively high LH levels include
- Maldevelopment of the ovaries (e.g., in Turner syndrome)
- An exhausted ovarian reserve
- Early menopause
- Polycystic ovaries (PCOS)