Hormones of the Menstrual Cycle: FSH, LH, Progesterone, Estrogen | NEET PG 2026

This lady is 28 years old. She has periods that do not come regularly. Sometimes she has periods after 35 days. Sometimes after 60 days. The doctor did a test on the day of her period. The test results showed that her FSH level was 12 mIU/mL, her LH level was 18 mIU/mL, and her estradiol level was 25 pg/mL.

Her LH level was a lot higher than her FSH level. The doctor thinks that this lady might have ovarian syndrome before even doing an ultrasound.

This one test, which was done at the time, and the results were read correctly, helps the doctor figure out what is wrong with the lady's polycystic ovarian syndrome. The polycystic ovarian syndrome is suspected because of the LH level and low FSH level.

Understanding menstrual cycle hormones is more than simply physiology; it is essential for identifying infertility, prescribing contraception, and managing menstrual problems. 

QUICK ANSWER

Four important hormones work together to control the menstrual cycle. FSH (follicle-stimulating hormone) increases follicular development and estrogen synthesis. LH (luteinizing hormone) stimulates ovulation and maintains the corpus luteum. Estrogen increases endometrial growth and has both a negative and positive effect on gonadotropin levels.

Progesterone converts proliferative endometrium to secretory endometrium, which preserves early pregnancy. The average cycle duration is 28±7 days, with ovulation happening 14 days before the next menstruation.

NEET PG RELEVANCE

Menstrual cycle hormones occur in 5-8 questions in NEET PG exams each year. The study focuses on day-specific hormone levels, the LH surge mechanism, the two-cell two-gonadotropin theory, feedback control, and clinical correlations. Recent works have emphasized GnRH pulsatility, inhibin activities, and the hormonal basis of contraception.

What Controls the Menstrual Cycle?

Here are some things that control the cycle:

• The ovaries produce estrogen and progesterone
• The brain sends signals to the ovaries
• Estrogen and progesterone control the growth of the lining of the uterus
• The menstrual cycle is controlled by the hormones estrogen and progesterone. Estrogen and progesterone are very important for the cycle.
• It is controlled by the pituitary-ovarian axis, which is like a system with many levels. Each level of the cycle system tells the next level what to do, and it also gets information back from the level below it. The menstrual cycle is very connected to the hypothalamic-pituitary-ovarian axis.
• Think of this system like a company. The hypothalamus is like the boss of the company, giving instructions. The pituitary is like the people in charge of departments, taking those instructions and making specific plans.
• The ovaries are like the employees who do the work, like growing follicles and making hormones. This system is not like a regular company because the employees are always talking back to the people in charge, and that changes what the bosses decide to do.
• The ovaries are always reporting back to the pituitary. That helps the pituitary make new decisions. The hypothalamus is also getting feedback from the ovaries.
• That helps it give new instructions. The ovaries, the pituitary, and the hypothalamus are all working together. They are always talking to each other.
• This hormone is released in a way that it comes out in pulses from a place called the arcuate nucleus. The number of pulses is very important: when the pulses come quickly, like every sixty to ninety minutes, it helps our body make more of a hormone called LH.
• On the other hand, when the pulses come more slowly, like every two to four hours, it helps our body make more of a hormone called FSH. This is how one hormone, GnRH, is able to control two hormones, LH and FSH, which do different things in our body.
• The anterior pituitary does something when it gets a signal from GnRH. It releases two hormones called FSH and LH from special cells called gonadotroph cells. These hormones are made up of two parts. An alpha part and a beta part. The alpha part is the same for both FSH and LH hormones. The beta part is different. This difference, in part, is what helps these hormones do their jobs.
• Both FSH and LH hormones travel to the ovaries. At the ovaries, they help with the development of follicles, which is a pretty important job. They also help the ovaries release an egg, which is called ovulation. They help the ovaries make a special structure called the corpus luteum work properly.
• The cycle length is usually around 28 days. It can be anywhere from 21 to 35 days. The time before you ovulate, which is called the phase, is different for everyone. On the other hand, the time after you ovulate, which is called the luteal phase, is almost always 14 days, give or take a couple of days.
• This is a reliable pattern, so doctors can figure out when you ovulated by counting back 14 days from when your next period starts, and that is a really useful thing to know about the menstrual cycle and the menstrual cycle in general.

What is FSH and What Does It Do?

FSH is short for Follicle Stimulating Hormone. It is made by a gland in our brains. This gland is called the gland. The pituitary gland sends FSH into our bloodstream. Then FSH goes to our ovaries or testes. Helps them work properly. FSH is very important for our health. It helps our bodies make babies. It is a hormone that helps people have children.

Also Read: Physiology Important Questions For NEET PG/FMGE

FSH Functions in the Ovary

• Follicular recruitment is what happens at the beginning of each cycle. At this time, the level of FSH in the body starts to increase. This rise in FSH helps to save a group of follicles in the ovaries that're about to die. These follicles are usually around 2 to 5 millimeters in size. If the body does not produce FSH, these follicles will die. 
• There is a period of time when these follicles really need FSH to survive. This period is called the "FSH window". During the FSH window, follicles, like the recruitment, depend on FSH, or they will die. The follicular recruitment and the FSH window are very important for the survival of the follicles.
• The hormone FSH helps the granulosa cells make more of the enzyme aromatase. This enzyme is also known as CYP19. It does an important job, which is to change androgens into estrogens. Theca cells make androgens when they are influenced by the hormone LH. 
• Then the granulosa cells take these androgens. Turn them into estradiol. This is how the granulosa cells and theca cells work together. This teamwork is the basis for what we call the two-cell two-gonadotropin theory. This theory is something that a lot of people studying for the PG exams need to know.
• When the follicles in the body get ready, the FSH helps the LH receptor to be made on the granulosa cells. The LH receptor is very important for this to happen. The FSH helps make the LH receptor on the granulosa cells.
• The production of Inhibin B is very important. Inhibin B is made when FSH helps the granulosa cells. These cells then make Inhibin B. The Inhibin B goes back. Stops the FSH from being made. This is how the body picks one follicle. 
• FSH rises in the early follicular phase (days 1-5), reaching 5-20 mIU/mL. As estradiol rises from the growing dominant follicle, negative feedback suppresses FSH. A small FSH surge accompanies the LH surge at mid-cycle.
• FSH remains low during the luteal phase, rising again as the corpus luteum regresses and estrogen/progesterone fall—this late luteal FSH rise initiates the next cycle's follicular recruitment.

What is LH and What Does It Do?

The Luteinizing hormone is really similar to the FSH hormone. They have the alpha subunit, but the beta subunit is different. This difference in the subunit is what allows the Luteinizing hormone to bind to different receptors. The Luteinizing hormone has its special way of binding to receptors because of this unique beta subunit.

LH Functions in the Ovary

• After the woman ovulates, LH also affects the granulosa-lutein cells. So LH is really important for theca cells and the granulosa-lutein cells, especially when it comes to LH and how it works with these cells.
• LH binds to the receptors on theca cells. This does a couple of things. It helps theca cells take in cholesterol. It also helps them make enzymes that are needed to make steroids. Theca cells then use this cholesterol to make androgens. These androgens are things like androstenedione and testosterone. They move into the granulosa cells that are nearby. The granulosa cells then change these androgens into estrogen. 
• The ovulation trigger is the middle of the cycle when the LH surge happens. This is when the LH level goes up to 25-100 /mL. When this happens, ovulation starts within 34-36 hours. The LH does things. It starts with enzymes, like collagenases and plasmin, that break down the wall of the follicle. This makes the wall weaker. The LH also helps make prostaglandin, which makes the smooth muscle contract.
• When this happens, the cumulus-oocyte complex is released. The oocyte is also. It finishes the first part of meiosis. Then it stops at the part, which is called metaphase II. The ovulation trigger and the LH surge are very important for this to happen. The ovulation trigger is what starts the process.
• The corpus luteum needs support after the body releases an egg. The hormone LH helps the corpus luteum. It makes the corpus luteum produce progesterone and estrogen.

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The LH Surge Mechanism

• The Luteinizing Hormone surge is an example of positive feedback, which is something that does not happen very often in the study of hormones. Here is what happens:
• Rising estradiol from the dominant follicle reaches threshold (>200 pg/mL sustained for >50 hours)
• High estrogen switches from negative to positive feedback at the pituitary level
• Estrogen helps the gonadotrophs in our body get ready to respond to something called GnRH. When this happens, it can also make the hypothalamus release a surge of GnRH. 
• After ovulation happens, it usually takes place in 34 to 36 hours. The time for ovulation to occur is 34 to 36 hours. When a woman is going to ovulate, ovulation will follow in 34 to 36 hours.
• This mechanism explains why only one follicle typically ovulates—only the dominant follicle produces sufficient estrogen to trigger the surge. It also explains why exogenous estrogen in combined oral contraceptives prevents ovulation by suppressing the natural estrogen rise.

What is Estrogen and What Does It Do?

The body makes something called estrogens. These are kinds of steroids that have 18 carbon atoms. They are made mostly by things in our body called granulosa cells. These cells make something called estradiol. 

Estrogen Functions

Reproductive tract effects:

• It helps the glands and the tissue that supports them to grow. This growth makes the endometrium thicker. It goes from being one to two millimeters thick after a woman has her period to being eight to twelve millimeters thick. The endometrium also starts to make receptors for progesterone. This gets the endometrium ready for when progesterone will help it get ready for a pregnancy. 
• This means it helps the sperm to move and fertilize the egg. The cervix produces this kind of mucus to help with fertilization.
• Fallopian tubes: Increase ciliary beat frequency and tubal motility, facilitating ovum transport.

Systemic effects:

• When women go through menopause, and they do not have estrogen, they can lose bone really fast. This is bad for the bone because it can get weak. Bone needs to stay strong and healthy. When estrogen levels are low, as during menopause, it can be a problem for the bones.
• Lipids have an effect on our bodies. They increase the cholesterol, which is called HDL, and decrease the bad cholesterol, which is called LDL. This is very good for our hearts.
• Coagulation is really important. It helps the liver make things that stop bleeding, like clotting factors. These clotting factors are called II, VII, IX, and X. When the liver makes more of these, it can cause blood clots to form. 
• Breast: Stimulates ductal growth and fat deposition.

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What is Progesterone and What Does It Do?

• The body makes a helper called Progesterone. This Progesterone is made mostly by the corpus luteum after the body releases an egg. Then something cool happens. The placenta starts making Progesterone after about 8 to 10 weeks when a woman is pregnant. The Progesterone is really important. It is a type of steroid that has 21 carbon atoms, which is why it is called a C21 steroid. The Progesterone helps the body get ready for a baby.

Progesterone Functions

Reproductive tract effects:

• This creates an environment for implantation of the endometrium. The cervix makes a sticky mucus that is bad for sperm. This mucus does not let the sperm get through. That is why some birth control methods that only use progestin can still work even if they do not stop the woman from ovulating. 
• The myometrium is really important because it helps keep the uterus from contracting too much. This is done by making the uterus less sensitive to oxytocin and by reducing the amount of prostaglandin that is made. 
• The breast is where milk is made. It gets ready for this by growing the parts that make the milk, which are called lobulo-alveolar. This is so the breast can make milk to feed a baby.

Systemic effects:

• Thermogenic: Raises basal body temperature by 0.3-0.5°C post-ovulation (basis for BBT charting to confirm ovulation)
• Respiratory: Stimulates ventilation, lowering PaCO2 (compensatory respiratory alkalosis of pregnancy)
• Central Nervous System or CNS. It helps people relax by affecting the GABA receptors in the brain. The Central Nervous System does this to produce a calming effect, which is also known as sedation. 

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Progesterone Feedback

The hormone Progesterone has a big effect on the HPO axis, and it is all bad. Progesterone slows down the frequency of GnRH pulses, which means it helps the body make FSH and less LH. The Progesterone is really good at slowing things down and suppressing the gland, which is why it has such a big impact on the HPO axis and the hormones that the body makes, like FSH and LH.

This negative feedback explains that there is something with the thing we are talking about, which is the negative feedback. The negative feedback is telling us that something is not good. We need to look at the feedback and figure out what the problem is with the negative feedback.

Day-by-Day Hormone Changes

Understanding cycle-day-specific hormone levels is essential for interpreting fertility workups and timing interventions.

Follicular Phase (Days 1-14)

Days 1-5 (Early follicular/Menstruation):

• FSH rising (5-20 mIU/mL)—recruits follicular cohort, LH low (2-10 mIU/mL)
• Progesterone low (<1 ng/mL)

Days 6-12 (Mid-follicular):

• FSH declining (negative feedback from rising estradiol)
• The dominant follicle is the one that gets chosen. It is usually the largest one that is most sensitive to FSH. 
• The level of Estradiol is going up fast. It is increasing from 100 to 400 pg/mL. 
• The follicle actually grows two millimeters every day. 

Days 12-14 (Late follicular/Periovulatory):

• Estradiol peaks (>200 pg/mL triggers positive feedback.
• LH surge (25-100 mIU/mL)—onset 34-36 hours before ovulation
• FSH small coincident surge
• Ovulation happens fourteen days before the next period. This is when the body releases an egg from the ovary, and it is ready to be fertilized. 

Luteal Phase (Days 15-28)

• Days 15-21 (Early-mid luteal): Corpus luteum forms from ruptured follicle
• The level of progesterone is 5 to 20 ng/mL by the twenty-first day. The progesterone level is very low at first. Then the progesterone rises dramatically. 
• Estradiol secondary rise (100-200 pg/mL)

Days 22-28 (Late luteal):

• When there is no pregnancy, and the woman is not producing the hormone hCG, the corpus luteum will shrink down. 
• The corpus luteum is a part of the body that plays a role in pregnancy. So if the woman is not pregnant, the corpus luteum will go away. This is what happens without hCG, and without a pregnancy, the corpus luteum regresses.
• The levels of progesterone and estradiol really drop a lot.
• The amount of progesterone and estradiol in the body goes down quickly.
• The endometrial spiral arteries get smaller and constrict. This means that the endometrial spiral arteries are tightening up and reducing the flow of blood. 
• Follicle Stimulating Hormone begins to rise, which means the body is getting ready for the cycle of recruitment of follicles in the ovaries. This is when the Follicle Stimulating Hormone starts to increase, and it helps to prepare the body for the menstrual cycle and the release of an egg from the ovaries.
• When a woman gets her period, that is considered Day 1 of her menstrual cycle. 

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High-Yield Points for NEET PG

• FSH acts on granulosa cells; LH acts on theca cells—this is the two-cell two-gonadotropin theory
• Aromatase (CYP19) converts androgens to estrogens in granulosa cells; FSH induces aromatase expression
• LH surge occurs when estradiol >200 pg/mL for >50 hours — positive feedback; ovulation follows in 34-36 hours
• Luteal phase is constant at 14±2 days; follicular phase length varies (explains irregular cycle lengths)
• Day 3 FSH >10 mIU/mL suggests diminished ovarian reserve; Day 21 progesterone >3 ng/mL confirms ovulation
• Inhibin B (follicular phase) and Inhibin A (luteal phase) selectively suppress FSH without affecting LH
• GnRH pulsatility determines gonadotropin ratio: fast pulses (60-90 min) favor LH; slow pulses (2-4 hr) favor FSH
• Progesterone raises BBT by 0.3-0.5°C — a biphasic temperature chart confirms ovulation retrospectively
• LH: FSH ratio >2:1 suggests PCOS — excess LH drives theca androgen production
• Combined OCP prevents ovulation by suppressing gonadotropins through estrogen/progestin negative feedback

Mnemonic for hormone sources: "FSH Favors Granulosa; LH Loves Theca."

Mnemonic for estrogen effects on cervical mucus: "Estrogen = Easy entry" (thin, watery, sperm-friendly)

Mnemonic for progesterone: "Pro-gestation" — supports pregnancy (secretory endometrium, quiet uterus, thick mucus)

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Frequently Asked Questions

What is the difference between FSH and LH functions?

FSH acts primarily on granulosa cells, stimulating follicular growth, aromatase expression (for estrogen synthesis), and inhibin B production. LH acts on theca cells to produce androgens (estrogen precursors) and triggers ovulation through the mid-cycle surge. After ovulation, LH maintains corpus luteum function. FSH recruits; LH matures and triggers.

When does the LH surge occur, and what triggers it?

The LH surge occurs approximately 34-36 hours before ovulation, typically around cycle day 12-14. It is triggered when estradiol from the dominant follicle exceeds 200 pg/mL and remains elevated for more than 50 hours. This sustained high estrogen switches feedback from negative to positive, causing massive LH release that initiates ovulation.

Why is Day 21 progesterone measured?

Day 21 (or 7 days post-ovulation) represents the mid-luteal phase when progesterone peaks. A level >3 ng/mL confirms ovulation occurred; levels >10 ng/mL suggest adequate luteal function. In irregular cycles, the test should be timed 7 days after suspected ovulation rather than fixed at Day 21 to avoid false-low results from mistiming.

How do oral contraceptives prevent pregnancy?

Combined oral contraceptives (estrogen + progestin) primarily prevent ovulation by suppressing the LH surge through negative feedback. Secondary mechanisms include thickened cervical mucus (impeding sperm), altered tubal motility, and endometrial thinning (reducing implantation receptivity). Progestin-only methods rely more heavily on cervical mucus changes and may not consistently suppress ovulation.

What causes PCOS hormone imbalance?

PCOS features elevated LH with relatively normal/low FSH, creating an LH: FSH ratio >2:1. Excess LH overstimulates theca cells, producing excessive androgens. Insufficient FSH fails to adequately stimulate granulosa aromatase, leaving androgens unconverted to estrogens. The resulting hyperandrogenism causes hirsutism, acne, and anovulation. Insulin resistance further amplifies ovarian androgen production.

What is the role of inhibin in the menstrual cycle?

Inhibins are glycoprotein hormones that selectively suppress FSH secretion without affecting LH. Inhibin B, produced by granulosa cells during the follicular phase, helps select the dominant follicle by suppressing FSH and withdrawing support from smaller follicles. Inhibin A, produced by the corpus luteum during the luteal phase, maintains FSH suppression. Falling inhibin with corpus luteum regression allows FSH rise for the next cycle recruitment.

CLINICAL PEARL

The menstrual cycle is like a conversation between the brain and the ovary. The. The ovaries talk to each other using hormones. When a woman has menstrual cycles, we should listen to what the hormones are saying to figure out where the conversation is going wrong. If a woman has FSH and low estradiol, it means the ovary is not responding properly. This is because the ovary is not producing eggs, which is also known as diminished reserve.

On the one hand, if a woman has high LH and normal FSH, it means the ratio of these hormones is not right. This can be a sign of a condition called Polycystic Ovary Syndrome or PCOS. If a woman has FSH and low LH, it means the pituitary gland is not sending the right signals to the ovary. The pituitary gland is like a messenger between the brain and the ovary. So when it is not working properly, it is called hypogonadotropic.

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