Follicle Stimulating Hormone - All You Need To Know About FSH

Written By Nivetha Arulraj - March 06, 2025

Read Time - 5 min read

Imagine a relatively empty and sad kitchen. When you're hungry, you have to use extra effort to order takeout, go to the store, or step out for a meal. But when you’re feeling full — it requires way less energy to feel satiated. Similarly, women with normal or high ovarian reserve have a sufficient production of estrogen and progesterone from small follicles (little sacs that hold the eggs) early in the menstrual cycle, which maintains FSH at a low level. With the onset of age, the number of eggs you have decreases. As a result, your body works harder to mature a follicle. Therefore, your FSH levels rise because your body needs more energy to find and grow a follicle. It could be a symptom of poor ovarian reserve if the body requires high doses of FSH to kick-start this maturation.¹

What Is Follicle Stimulating Hormone?

Follicle Stimulating hormone (FSH), is a gonadotropic hormone secreted by the pituitary gland (a pea shaped tiny organ found at the base of the brain) and then to the bloodstream. It facilitates sexual growth and development by stimulating the growth of follicles in females, thereby, initiating ovulation. ¹

Importance Of Follicle Stimulating Hormone

Ovulation, fertilization, and pregnancy require a mature egg and this is taken care of by FSH. FSH levels are usually lowest at the start of the menstrual cycle and gradually rise. This rise in the levels of FSH causes a follicle (fluid filled sac that contains the egg) to grow.
As the follicles increase in number, they release Estradiol (E2) by stimulating the granulosa cells present in the follicles. In turn, these higher levels of Estradiol tell the pituitary gland to make less FSH which stimulates the process of ovulation - release of an egg. High Estradiol (E2) levels can suppress FSH and lead to inaccurate assessment of FSH levels alone. Also, testing FSH alone may not give a good indication of the ovarian reserve due to its inter and intra cycle variability.² It's best suggested that both the hormones must be tested together to get a clear picture.
Luteinizing hormone (a gonadotropic hormone produced by the pituitary gland which plays a key role in controlling the ovarian function) in synergy with FSH triggers the follicular growth. Thus, the complementary action of LH and FSH results in the growth of the follicles that ultimately leads to the ovulation process.³
In short, testing FSH and E2 along with LH provides insights on how the ovaries and pituitary gland are working together and testing Anti Mullerian Hormone (AMH) along with FSH, LH and E2 is a more holistic and accurate approach towards understanding ovarian reserve.

Role Of FSH:

1. Understanding Primary Ovarian Insufficiency (POI):

Fact:

Primary Ovarian Insufficiency, previously known as Premature Ovarian Failure (POF) occurs due to the dysfunction of ovarian follicles which results in early cessation of menstrual cycle (before the age of 40). Usually, elevated FSH levels, low levels of E2 coupled with amenorrhea ⁴ (absent menstrual cycles) for at least 4 months indicates the risk of POI. The same is repeated to confirm diagnosis at least a month apart. ^{5 6}

Implication:

In the event you are at an elevated risk of POI, initiate a conversation with your fertility specialist, take corrective measures beforehand and ensure your future plans are not compromised.

2. Understanding Functional Hypothalamic Amenorrhea (FHA):

Fact:

Functional Hypothalamic Amenorrhea is a form of amenorrhea (absence of menstruation) that results due various causes such as stress, weight loss and excessive exercise. This condition is characterized by abnormal GnRH (Gonadotropin Releasing Hormone) secretion which in turn disturbs the secretion of gonadotropins - FSH and LH which may negatively impact the process of fertilization. Generally, women diagnosed with FHA are more likely to show elevated E2 levels and low or normal levels of FSH and LH.⁷

Implication:

Should your results indicate an elevated risk for FHA, consulting your doctor and understanding the cause of the condition coupled with medications and follow-up treatment procedures can help you manage the condition effectively and efficiently.

When Can I Take Up The FSH Test?

By measuring the FSH levels, one can get insights into their ovarian function. Generally, your FSH levels fluctuate throughout the menstrual period. Here, timing is crucial. In order to get an accurate picture of your FSH levels you are advised to take up the test during Day 3 of your cycle.

What Can Differing FSH Levels Tell You?

1. Normal FSH Levels

The normal levels of FSH usually range between 1.37-9.9 IU/L.

2. High FSH Levels

In women, FSH levels increase as the production of eggs in the body decreases. If your ovarian reserve is declining, the follicles are less sensitive to FSH, and it is harder for the egg to mature and ovulate. In response, your body produces more FSH to try to stimulate egg production. This means that your body is struggling to make eggs and is trying to compensate. High levels of FSH also helps indicate the possibility of the woman undergoing menopause since significant changes in the levels of FSH can be witnessed pre menopause or during menopause. It may also indicate the risk of Primary Ovarian Insufficiency (POI) ⁸, for which a confirmation test of other related hormones is also required (E2). ⁹

3. Low FSH Levels

FSH is expected to be low around day 3 of your cycle. This indicates your ovaries don't have to work super hard to produce and mature an egg. But as you get older this trend changes and FSH levels increase in the blood. Low levels of FSH may also indicate the risk of amenorrhea coupled elevated levels of E2.