Luteinising hormone is an important cycling hormone, involved in the regulation of the menstrual cycle and ovulation. But what happens when our levels get a little off balance? In this article, we’ll explain exactly what luteinising hormone is, how it works, and take a deep dive into its importance for female fertility. We’ll also take a look at LH levels and why they’re important, as well as how to recognise the symptoms of low or high LH. Quick facts: What is Luteinising Hormone (LH)?  Luteinising hormone (LH) plays a huge role when it comes to fertility and ovulation, despite it being one of the lesser-known cycling hormones. Luteinising hormone (LH) is what’s known as a gonadotropin hormone. There are only two types of this hormone, LH and its partner in crime, follicle-stimulating hormone (FSH). Gonadotropins are hormones that are released from the pituitary gland in the brain, into the bloodstream where they are transported to the gonads—or ovaries in those assigned female-at-birth and the testes in those assigned male-at-birth. LH has 3 main functions in those assigned-female-at-birth:  Oestrogen production LH works in tandem with FSH to stimulate the ovaries and surrounding cells to produce oestrogen. First, LH stimulates what’s known as theca cells in the ovaries, which then produce testosterone. Once testosterone is abundant, nearby granulosa cells are then stimulated by FSH to produce an enzyme called aromatase, which converts the testosterone into a type of oestrogen, oestradiol, or E2. Without the correct functioning of LH or FSH, testosterone and oestrogen production can become impacted. Ovulation LH is also crucial for successful ovulation. First, FSH stimulates the growth of follicles (small sacs that contain your eggs) in your ovaries. A number of eggs mature during the first half of your cycle, but only one gets released during ovulation—usually the ‘most mature’ follicle. In the days leading up to ovulation, this follicle increases its sensitivity to LH. It gradually produces more and more E2 and when this reaches a certain level, the pituitary gland releases a surge of LH. This LH surge is what causes the follicle to rupture and release the mature egg into the fallopian tube—triggering ovulation. Progesterone production After ovulation has occurred, LH stimulates the now empty follicle to start producing progesterone throughout the second half of the menstrual cycle—also known as the luteal phase. Both progesterone and E2 released by the empty follicle are intended to support conception, implantation and the early stages of pregnancy. However, if the egg is not fertilised and no embryo implants into the uterus, the empty follicle stops producing these hormones and eventually wastes away at the end of the menstrual cycle. What are normal LH levels in women? LH levels in women, or those assigned-female-at-birth, fluctuate during the menstrual cycle—so their levels will vary depending on where you are in your monthly cycle. LH levels can also vary depending on an individual’s age and whether they’re pregnant. Normal LH levels for women before menopause are around 5-25 IU/L, depending on the stage of the menstrual cycle. After menopause, normal LH levels range from around 14-52 IU/L. LH levels during the menstrual cycle Let’s take a closer look at how LH fluctuates during the menstrual cycle. As we mentioned earlier, a dramatic surge in LH around the middle of the cycle triggers ovulation. But after ovulation, LH production is dulled by rising levels of progesterone. If no pregnancy occurs and progesterone levels fall, LH production will start again anew at the beginning of the next cycle. LH levels during pregnancy During early pregnancy, LH levels remain low—blocked by continued progesterone production. High levels of human chorionic gonadotropin (hCG) released throughout pregnancy also ensure that they stay low throughout pregnancy, so no further ovulation is triggered. LH levels in menopause During menopause, LH levels become elevated, although this can vary from person to person. This increase in LH levels happen as a result of the general decline in hormone production by the ovaries. When the ovaries stop producing as much oestrogen and progesterone, the pituitary responds by increasing the production of FSH and LH, in an attempt to stimulate the ovaries. However, the ovaries become less responsive and, instead, LH levels rise. This rise in LH levels is associated with a lot of the typical symptoms of menopause, including hot flashes and night sweats. After menopause, LH levels can decline by around 30-40%. High LH levels High LH levels in females outside of normal menstrual cycle fluctuations can cause fertility problems, irregular periods and early puberty. High LH levels are often seen in people with primary ovarian insufficiency and in those with polycystic ovary syndrome (PCOS) often have elevated LH compared to their FSH. This unusual imbalance can lead to irregular periods and the overproduction of testosterone, both key symptoms of PCOS. Sometimes LH levels can become elevated due to dietary and lifestyle factors, including: Symptoms of high LH levels Symptoms of high LH levels in females are more related to the underlying cause than the LH itself. However, some of the most common symptoms associated with the causes of high LH levels include: How to lower LH levels If your LH levels are elevated and you are a regular smoker or drinker, consider taking steps to reduce these habits. If you’re trying to conceive, consider cutting alcohol and cigarettes completely as this will improve your chances of conception and prevent harmful effects to the baby during pregnancy. Low LH levels There are also a number of reasons why low LH levels might occur. Meningitis infections that have occurred in the last 12 months have been linked to low LH levels and so have eating disorders. Sometimes, LH levels can be decreased due to dietary and lifestyle factors as well as certain medications including: Low LH levels in females can lead to problems with ovulation. This includes anovulation, which is not ovulating at all. This can also lead to problems with menstruation, such as irregular, missing, or complete cessation of periods. Symptoms […]