Question explored with the scientific record
What does having consistently low FSH but normal LH mean
The short version: low FSH with normal LH points to a problem at the pituitary level, not the hypothalamus, and the evidence here does not include a single study that tested this exact pattern in humans.
The retrieved studies describe the opposite problem—low FSH and low LH together (hypogonadotropic hypogonadism) from a hypothalamic defect [1]. That is a different condition. One study in mice found that a brain-specific selenium deficiency raised LH but lowered FSH, which is closer to your pattern, but that is a mouse model from 2025, not human data [2]. The rest of the evidence covers PCOS rats, stallions, and women on naltrexone—none of which answer your question [3, 4, 5, 6].
What the evidence does not contain: any human study comparing people with isolated low FSH and normal LH to healthy controls. No trial. No cohort. No case series. The mechanism that would produce this pattern is a pituitary defect that selectively impairs FSH secretion while leaving LH intact. That could be a mutation in the FSH beta subunit, a problem with the pituitary's response to GnRH that affects FSH more than LH, or a tumor or infiltrative disease in the pituitary. But the evidence here does not test any of those.
My call: the evidence does not answer your question. The pattern you describe is rare enough that no study in this retrieval examined it. A clinical workup—pituitary imaging, GnRH stimulation testing, and genetic testing for FSH beta mutations—would be the standard next step, but the evidence here does not support or rule out any specific cause. Confidence: not clear—the retrieval simply does not cover this question.
Sources used 6
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Hypogonadism and CHARGE association
Nine individuals with CHARGE association exhibit hypogonadotropic hypogonadism with low or undetectable LH and FSH across infancy to adulthood, implicating central hypothalamic or pituitary defects and supporting early LH/FSH testing for diagnosis.
DOI: 10.1002/1096-8628(20000918)94:3<228::aid-ajmg8>3.0.co;2-h -
Central SELENOT deficiency impairs gonadotrope axis function, sexual behavior and fertility in male and female mice
Brain-specific SELENOT deficiency in mice disrupts GnRH neuron regulation and the gonadotrope axis, causing increased GnRH and LH signaling with altered LH pulsatility, hormonal imbalances, disrupted estrous cycles, abnormal sexual behavior, ovarian/testicular pathology, and red…
DOI: 10.1172/jci.insight.189775 -
The hypothalamic-pituitary-luteal axis in women: Effects of long-term orally active opioid antagonist (naltrexone) administration
A randomized study in 14 normovulatory women showing that seven days of oral naltrexone during the luteal phase enhances GnRH-driven gonadotropin pulsatility (increasing LH pulse number and amplitude and inducing FSH pulses), raises baseline progesterone in controls but not with…
DOI: 10.1007/bf03347986 -
GnRH Therapy for Subfertile Stallions
GnRH therapy may improve fertility in some subfertile stallions with moderate testicular degeneration, but it is not a cure-all and is unlikely to help advanced cases; it appears safe because horses are resistant to GnRH-induced downregulation.
DOI: 10.1016/s0749-0739(17)30301-2 -
Effects of electroacupuncture on the kisspeptin-gonadotropin-releasing hormone (GnRH) /luteinizing hormone (LH) neural circuit abnormalities and androgen receptor expression of kisspeptin/neurokinin B/dynorphin neurons in PCOS rats
Electroacupuncture at CV4 reverses letrozole-induced PCOS-like reproductive and brain neuroendocrine abnormalities in rats, likely by dampening androgen activity on KNDy neurons and normalizing kisspeptin-GnRH/LH signaling.
DOI: 10.1186/s13048-022-01078-x -
Role of exercise in the Pathogenesis of the Amenorrhea Associated with anorexia nervosa
Examines how weight loss and exercise contribute to amenorrhea, distinguishing hypothalamic GnRH deficiency in anorexia nervosa from a weight/ovary-related pattern in exercise-induced amenorrhea, and highlighting differing hormonal responses and implications for recovery.
DOI: 10.1016/s0197-0070(83)80223-x