What Is LH (Luteinizing Hormone, Follicular)? Normal vs Optimal Range Explained

LH is the pituitary signal that triggers the final maturation and release of the dominant ovarian follicle each month. In the early follicular phase (days 2–5 of the menstrual cycle), LH should be relatively low and roughly equal to FSH in a 1:1 ratio. The CTD maps over 580 compound interactions affecting LH signaling and gonadotropin-releasing hormone pathways. Lab reference ranges extending to 15 mIU/mL in the follicular phase include values where the LH-to-FSH ratio is already elevated above 2:1—the diagnostic hallmark of PCOS that drives excess ovarian androgen production and anovulation. LH above 10 mIU/mL in the early follicular phase, particularly when FSH remains below 5, creates the disproportionate ratio that stimulates theca cells to overproduce testosterone, DHEA-S, and androstenedione. The optimal range of 2–10 mIU/mL reflects the follicular LH level consistent with normal ovulatory cycling and balanced gonadotropin signaling.

The mid-cycle LH surge—a dramatic rise from baseline to 14–96 mIU/mL lasting 24–48 hours—is what triggers ovulation. PubMed indexes over 45,000 publications on LH, with clinical analyses demonstrating that the surge must be both sufficiently large and precisely timed for successful ovulation. Without an adequate LH surge, the dominant follicle fails to rupture, no egg is released, and no corpus luteum forms to produce the progesterone needed to support a potential pregnancy. Ovulation predictor kits detect this LH surge in urine, providing a window for timed intercourse or intrauterine insemination. In women with PCOS, the tonically elevated LH often produces erratic or absent surges, explaining the anovulatory infertility that characterizes the condition.

Several clinical contexts alter follicular-phase LH in diagnostically important ways. FAERS data document gonadotropin changes across over 60 medication entries, including oral contraceptives that suppress LH release as their primary contraceptive mechanism. In perimenopause, both LH and FSH rise as declining ovarian function weakens the negative feedback that normally holds pituitary gonadotropins in check. In hypothalamic amenorrhea—commonly caused by excessive exercise, low body weight, or chronic stress—both LH and FSH drop below normal because the hypothalamus stops producing GnRH, shutting down the entire reproductive axis. Distinguishing elevated LH from PCOS versus rising LH from perimenopause versus suppressed LH from hypothalamic amenorrhea requires interpreting LH in the context of FSH, estradiol, progesterone, and clinical symptoms rather than as an isolated number.