What Does LH Do?
Understanding the Hormone That Helps Trigger Ovulation
"LH is the hormone that tells your ovary it's time to release an egg."
Why This Matters
LH is one of the most important hormones involved in fertility.
If you've had fertility blood tests, you've probably seen LH (Luteinising Hormone) listed alongside FSH, AMH and progesterone.
But what exactly does it do?
And why does your healthcare professional measure it?
Understanding the role of LH can help you make sense of your fertility investigations and how your hormones work together throughout your menstrual cycle.
What Is LH?
LH stands for Luteinising Hormone.
It is produced by the pituitary gland, a small gland at the base of your brain.
Its main role is to help control your menstrual cycle by working closely with:
FSH (Follicle Stimulating Hormone)
Oestrogen
Progesterone
Together, these hormones coordinate the growth of an egg, ovulation and preparation for pregnancy.
What Does LH Do During the Menstrual Cycle?
LH has different jobs at different stages of your cycle.
Early in the Cycle
At the beginning of your cycle, LH works alongside FSH to support the growth of ovarian follicles.
These follicles contain immature eggs.
As one follicle becomes dominant, it produces increasing amounts of oestrogen.
Just Before Ovulation
As oestrogen reaches a certain level, your brain responds by releasing a large amount of LH.
This is known as the LH surge.
The LH surge tells the dominant follicle:
"It's time to release the egg."
Ovulation usually occurs around 24 to 36 hours after the LH surge begins.
After Ovulation
Once the egg has been released, LH helps the empty follicle become the corpus luteum.
The corpus luteum produces progesterone, which prepares the lining of the uterus for a possible pregnancy.
If pregnancy does not occur, LH levels fall and the next menstrual cycle begins.
Why Is LH Tested?
An LH blood test can help your healthcare professional understand:
Whether your hormones are working together normally.
Whether ovulation is likely to be occurring.
Whether there may be signs of conditions such as PCOS.
How your fertility hormones compare with one another.
LH is almost always interpreted alongside other hormone tests rather than on its own.
Is LH the Same as an Ovulation Test?
Not exactly.
Home ovulation tests detect the LH surge in urine.
A fertility blood test measures the amount of LH in your bloodstream at a particular moment.
Although both involve LH, they are used for different purposes.
What Happens If LH Levels Are Too High or Too Low?
LH levels naturally change throughout your menstrual cycle.
Sometimes an unusually high or low result may suggest that further investigation is needed.
However, one result on its own rarely provides all the answers.
Your healthcare professional will interpret your LH alongside:
FSH.
AMH.
Oestradiol.
Progesterone.
Ultrasound findings.
Your symptoms and menstrual history.
My Story
One thing I found confusing during fertility investigations was how many hormones were involved.
I could remember hearing about FSH and progesterone, but I had no idea where LH fitted in.
Looking back, I wish someone had simply explained that LH is the hormone that gives the final signal for ovulation to happen.
Once I understood that, the rest of the menstrual cycle suddenly made much more sense.
Questions Worth Asking
If you've had an LH blood test, you might ask:
Is my LH level what you'd expect for this stage of my cycle?
Am I likely to be ovulating?
How does my LH compare with my FSH?
Should I have other hormone tests?
What do my results mean overall?
I Wish Someone Had Explained...
I wish someone had explained that LH is like the starter's whistle in a race.
FSH prepares the egg.
The follicle grows.
Oestrogen rises.
Then LH blows the whistle that tells the ovary:
"Go!"
Without that signal, ovulation may not happen as expected.
Understanding that one simple role made all the different hormone names much less overwhelming.
Key Takeaways
✔ LH stands for Luteinising Hormone.
✔ It is produced by the pituitary gland.
✔ LH works closely with FSH, oestrogen and progesterone.
✔ The LH surge triggers ovulation.
✔ After ovulation, LH helps stimulate progesterone production.
✔ LH is usually interpreted alongside other fertility hormone tests.