Luteinizing hormone is a glycoprotein hormone released by the anterior pituitary that orchestrates ovulation and the formation of the corpus luteum, playing a central role in the menstrual cycle.
Quick Takeaways
- LH is released in a sharp surge that triggers the release of the mature egg.
- After ovulation, LH supports the corpus luteum to produce progesterone.
- Feedback from estrogen and progesterone fine‑tunes LH levels.
- Abnormal LH patterns can indicate fertility issues.
- Clinical LH tests help diagnose ovulatory disorders.
Hormone Basics: The Players in Reproductive Regulation
Understanding LH is easier when you see it in the context of the whole endocrine orchestra. Below are the key cast members, each introduced once with microdata.
Follicle‑stimulating hormone (FSH) is a pituitary hormone that drives follicle growth in the ovary and works alongside LH to prepare the egg for release.
Ovary is a female gonad that houses follicles, produces estrogen, and after ovulation becomes the site of the corpus luteum.
Estrogen is a steroid hormone secreted by growing follicles that modulates the uterine lining and provides positive feedback to LH secretion.
Progesterone is a hormone produced by the corpus luteum that stabilises the uterine lining and exerts negative feedback on LH release.
Hypothalamus is a brain region that secretes gonadotropin‑releasing hormone (GnRH) to stimulate LH and FSH release from the pituitary.
Pituitary gland (anterior pituitary) is a small endocrine organ that converts GnRH pulses into LH and FSH pulses.
Gonadotropin‑releasing hormone (GnRH) is a hypothalamic peptide that drives the pulsatile secretion of LH and FSH.
How LH Is Made and Controlled
The hypothalamus releases GnRH in bursts roughly every 60-90 minutes. These pulses travel through the hypophyseal portal system to the anterior pituitary, where they trigger the synthesis and secretion of LH (and FSH). The size of each LH pulse depends on two feedback loops:
- Estrogen positive feedback: When estradiol rises above ~200pg/mL during the late follicular phase, it flips from suppressing to amplifying LH release, setting the stage for the LH surge.
- Progesterone negative feedback: After ovulation, progesterone from the corpus luteum tells the hypothalamus and pituitary to tone down LH, preventing another surge too soon.
Age, body mass index, and stress can also tweak GnRH pulse frequency, indirectly influencing LH levels.
The LH Surge: The Spark that Fires Ovulation
About 24‑36 hours before the egg is released, the estrogen‑driven positive feedback creates a dramatic spike in LH - the famous LH surge. This surge has three critical actions:
- Follicle rupture: LH activates enzymes that weaken the follicular wall, allowing the oocyte to escape.
- Resumption of meiosis: The oocyte, paused at metaphase II, completes meiosis I and prepares for fertilisation.
- Corpus luteum formation: The collapsed follicle reorganises into the corpus luteum, which will later secrete progesterone.
Without a sufficient surge, the follicle may degenerate, leading to an anovulatory cycle - a common cause of infertility.
LH’s Role After Ovulation: Keeping the Uterus Ready
Once the egg leaves, LH continues to support the corpus luteum. Although LH levels drop from the surge, a basal secretion persists to maintain progesterone output. Progesterone then:
- Transforms the proliferative endometrium into a secretory one, ready for embryo implantation.
- Suppresses further LH surges via negative feedback, ensuring only one ovulation per cycle.
If fertilisation does not occur, the corpus luteum regresses around day10-12 of the luteal phase, progesterone falls, and the cycle restarts with a new rise in GnRH and LH.
Clinical Snapshots: When LH Goes Off‑Track
Doctors often look at LH patterns to diagnose reproductive problems:
- Polycystic ovary syndrome (PCOS): Elevated LH/FSH ratio (often >2) reflects disrupted GnRH pulse frequency.
- Hypothalamic amenorrhea: Low GnRH leads to low LH and absent ovulation, often linked to stress or low body weight.
- Premature ovarian failure: High gonadotropins (including LH) as the ovaries stop responding.
Blood tests measuring LH, usually timed on day3 of the cycle, help clinicians decide whether to prescribe ovulation‑inducing agents such as clomiphene or letrozole.
Side‑by‑Side: LH vs. FSH
| Attribute | Luteinizing hormone (LH) | Follicle‑stimulating hormone (FSH) |
|---|---|---|
| Primary target | Ovarian theca cells → androgen → estrogen; triggers ovulation | Ovarian granulosa cells → estrogen synthesis; supports follicle growth |
| Peak timing | Late follicular phase (LH surge) | Early‑mid follicular phase, steady low‑mid levels |
| Molecular weight (kDa) | ~30 | ~30 (identical beta subunit) |
| Clinical use | Triggering ovulation in assisted reproduction | Assessing ovarian reserve, stimulating follicle development |
Linking to the Bigger Picture
This article sits within a broader cluster on reproductive endocrinology. Wider topics include the hypothalamic‑pituitary‑gonadal (HPG) axis, menstrual cycle disorders, and assisted reproductive technologies. Narrower follow‑ups could dive into "How GnRH analogues modulate LH for IVF" or "The impact of environmental endocrine disruptors on LH secretion".
Take‑Home Checklist
- LH surge = ovulation trigger.
- Estrogen positive feedback drives the surge; progesterone negative feedback ends it.
- Post‑ovulatory LH supports the corpus luteum and progesterone production.
- Abnormal LH patterns signal conditions like PCOS or hypothalamic amenorrhea.
- Clinical LH testing is a cornerstone of fertility work‑ups.
Frequently Asked Questions
What exactly is the LH surge?
The LH surge is a brief, sharp increase in luteinizing hormone that occurs about 24‑36hours before ovulation. Driven by high estradiol levels, it activates enzymes that rupture the mature follicle, releases the egg, and initiates corpus luteum formation.
How does estrogen influence LH release?
Early in the cycle estrogen exerts negative feedback, keeping LH low. When estradiol peaks above ~200pg/mL, the feedback flips to positive, amplifying GnRH pulse amplitude and causing the LH surge.
Can I measure my LH at home?
Yes, over‑the‑counter ovulation predictor kits (OPKs) detect the LH surge in urine. A positive test typically means ovulation will happen within the next 24‑36hours, which is useful for timing intercourse or insemination.
Why is LH often elevated in PCOS?
In PCOS, the hypothalamus emits faster GnRH pulses, favouring LH over FSH secretion. The resulting high LH/FSH ratio (commonly >2) promotes excess androgen production, contributing to the classic PCOS symptoms.
What happens to LH after pregnancy?
During pregnancy, high levels of hCG (human chorionic gonadotropin) mimic LH activity, while the mother’s own LH secretion remains suppressed by progesterone and estrogen feedback. LH levels stay low until after delivery.
Kerri Burden
September 26, 2025 AT 00:59The LH surge exemplifies a classic endocrine positive feedback loop, wherein rising estradiol from the dominant follicle flips its modulatory role and amplifies GnRH pulse amplitude. This pulsatile GnRH signal then precipitates a rapid LH release from the anterior pituitary, culminating in the ovulatory trigger. Notably, the LH surge also initiates the enzymatic cascade that weakens the follicular wall, facilitating oocyte extrusion. Post‑ovulation, basal LH maintains luteal progesterone synthesis, safeguarding endometrial receptivity. Dysregulation at any node-hypothalamic GnRH, pituitary LH secretion, or ovarian feedback-can manifest as anovulation or luteal phase defects.