Gonadotropins are hormones that control your reproductive system. They signal your ovaries or testes to produce sex hormones and develop eggs or sperm. There are three main gonadotropins: follicle-stimulating hormone (FSH), luteinizing hormone (LH), and human chorionic gonadotropin (hCG), which appears during pregnancy.
Where Gonadotropins Come From
FSH and LH are produced by specialized cells called gonadotropes in the anterior pituitary, a small gland at the base of the brain. These cells don’t release hormones on their own. They take instructions from the hypothalamus, a region just above the pituitary that acts as the brain’s hormonal command center.
The hypothalamus releases a signaling hormone called GnRH in short, rhythmic pulses into a network of blood vessels connecting it to the pituitary. Each pulse triggers the pituitary to release a burst of LH and FSH into the bloodstream. The speed of these pulses matters: slower pulses favor FSH release, while faster pulses favor LH. Between pulses, GnRH levels drop to nearly undetectable concentrations, and this on-off pattern is essential. Continuous, non-pulsing GnRH actually shuts gonadotropin production down rather than stimulating it.
This chain of signals, from hypothalamus to pituitary to gonads, is called the hypothalamic-pituitary-gonadal (HPG) axis. It runs on a feedback loop: when sex hormone levels rise high enough, they signal the hypothalamus and pituitary to ease off production. When levels drop, production ramps back up.
What FSH and LH Do in Women
In women, FSH and LH orchestrate the entire menstrual cycle. At the start of each cycle, FSH stimulates a group of immature follicles in the ovaries to begin growing. Each follicle contains an egg, and FSH drives these eggs toward maturity. As the follicles develop, they produce rising levels of estrogen.
LH works alongside FSH during this growth phase by acting on cells surrounding each follicle to produce androgens, which neighboring cells then convert into estrogen. This estrogen fuels further follicle development. Once estrogen reaches a critical threshold, it triggers a dramatic spike in LH release known as the LH surge. This surge is the direct trigger for ovulation: it activates enzymes that weaken the ovarian wall, allowing the mature egg to break through and enter the fallopian tube.
After ovulation, FSH and LH together transform what remains of the emptied follicle into the corpus luteum, a temporary structure that pumps out progesterone to prepare the uterine lining for a potential pregnancy. If no pregnancy occurs, the corpus luteum breaks down, progesterone and estrogen fall, menstruation begins, and rising FSH starts recruiting follicles for the next cycle.
What FSH and LH Do in Men
In men, LH controls testosterone production. It binds to Leydig cells, which sit in the tissue between the sperm-producing tubes of the testes. These cells respond by synthesizing and releasing testosterone into the bloodstream. High testosterone levels within the testes are a prerequisite for sperm production and maturation. LH also promotes the growth and maturation of Leydig cells themselves.
FSH targets a different cell type called Sertoli cells, which line the walls of the seminiferous tubules where sperm develop. Sertoli cells act as support structures for developing sperm, providing the signaling molecules and nutrients that germ cells need as they progress from immature precursors to fully formed sperm. Testosterone and FSH work together on Sertoli cells to initiate and maintain spermatogenesis. Neither hormone alone is sufficient for normal sperm production.
hCG During Pregnancy
Human chorionic gonadotropin is the third gonadotropin, and it only appears in significant amounts during pregnancy. It’s produced by cells in the developing placenta, not the pituitary. Because hCG is structurally similar to LH, it binds to the same receptor and essentially takes over LH’s job of keeping the corpus luteum alive.
This matters because the corpus luteum is the only source of progesterone in the first weeks of pregnancy, and progesterone is what keeps the uterine lining intact. Without hCG, the corpus luteum would break down, progesterone would drop, and the pregnancy would end. During the first six weeks, hCG drives the corpus luteum to secrete progesterone, estrogen, and related hormones. By about 11 weeks, the placenta itself produces enough progesterone to sustain the pregnancy independently.
Beyond maintaining the corpus luteum, hCG promotes blood vessel growth in the uterine lining, helps keep the uterine muscle relaxed, and plays a role in preventing the mother’s immune system from rejecting the embryo. It’s also the hormone detected by pregnancy tests, since it appears in blood and urine shortly after implantation.
Normal Levels and Testing
Doctors measure FSH and LH through a simple blood draw, typically to evaluate fertility, puberty timing, or menstrual irregularities. Normal FSH ranges vary considerably by sex and life stage. In adult men, FSH typically falls between 1.5 and 12.4 mIU/mL. In women of reproductive age, it ranges from about 4.7 to 21.5 mIU/mL, though it fluctuates throughout the menstrual cycle. After menopause, FSH rises sharply to between 25.8 and 134.8 mIU/mL because the ovaries are no longer producing enough estrogen to suppress pituitary output.
A single FSH or LH reading doesn’t always tell the full story, since these hormones pulse throughout the day and shift across the menstrual cycle. Your doctor may order multiple draws or time the test to a specific cycle day for a more accurate picture.
What Happens When Levels Are Too Low
When the brain produces too little FSH and LH, the condition is called hypogonadotropic hypogonadism. Without adequate gonadotropin signaling, the ovaries or testes don’t receive the instructions they need to produce sex hormones or develop eggs and sperm.
The effects depend on when the deficiency starts. If it begins before birth, it can affect genital development. If it starts before puberty, it can delay or prevent the typical changes of adolescence: muscle development, voice deepening, body hair growth, and breast development. In adults, it can cause infertility, low sex drive, fatigue, and loss of bone and muscle mass. Causes range from genetic conditions present from birth to acquired problems like pituitary injuries, certain infections, obesity, opioid use, and obstructive sleep apnea. Testosterone levels also naturally decline with age, though the rate varies widely from person to person.
Gonadotropins as Fertility Treatment
Injectable gonadotropins have been a cornerstone of fertility medicine since 1961, when they were first used to induce ovulation in women whose pituitary glands weren’t producing enough FSH and LH on their own. Today, synthetic and purified versions of FSH and LH are widely used for two main purposes: stimulating ovulation in women who don’t ovulate regularly, and stimulating multiple eggs to mature at once during IVF cycles.
Women with very low gonadotropin levels (a group sometimes classified as WHO Group I) typically need higher doses to get a response, while women who produce some gonadotropins but still don’t ovulate regularly often respond to lower doses. The treatment involves daily injections over a period of days to weeks, with regular ultrasound and blood monitoring to track how the ovaries are responding.
The most significant risk of gonadotropin therapy is ovarian hyperstimulation syndrome (OHSS), where the ovaries overrespond and swell, sometimes causing fluid to accumulate in the abdomen. Some degree of OHSS occurs in up to 33% of assisted reproduction cycles, though moderate to severe cases are less common, affecting roughly 3% to 8% of cycles. Women with high ovarian reserve are at the greatest risk. In one study of high responders, the overall OHSS rate was 15.5%, though the type of gonadotropin used made a meaningful difference: 9.7% with one formulation versus 21.4% with another. Monitoring during treatment helps catch the early signs so your doctor can adjust the protocol.