Luteinizing Hormone (LH): The Surge That Triggers Ovulation

• LH is made by your pituitary gland; its job is to trigger ovulation and then support the hormone-producing corpus luteum afterwards.
• A sharp mid-cycle LH surge (roughly 10-fold above baseline) sets off ovulation about 24-36 hours later — this is exactly what ovulation predictor kits detect.
• Ovulation kits are urine tests that turn positive when LH crosses a threshold; they predict ovulation but do not confirm it has happened.
• On a day 2-3 blood test, an LH-to-FSH ratio above 2:1 can support a PCOS diagnosis, but LH alone is never enough to diagnose it.
• High LH and FSH with low oestrogen can point to ovarian insufficiency or menopause; low LH and FSH can point to a hypothalamic or pituitary cause.
• LH testing is cheap and widely available across India (about Rs 300-600), and is usually ordered as part of a fertility hormone panel.

Luteinizing hormone is one of two gonadotropins — pituitary hormones that act on the ovaries (and, in men, the testes) to run reproduction. Its partner is follicle-stimulating hormone (FSH); the two work as a team, and they are usually measured together. You can read more about FSH and what it tells you in our guide to FSH and pregnancy.

LH is controlled by a three-part chain often called the HPG axis (hypothalamus-pituitary-gonad):

• The hypothalamus, a small region at the base of the brain, releases gonadotropin-releasing hormone (GnRH) in pulses. The speed of these pulses decides how much LH versus FSH the pituitary makes. (Interestingly, continuous GnRH switches LH and FSH off rather than on — which is exactly how GnRH-agonist fertility drugs work.)
• The pituitary gland responds to each GnRH pulse by releasing LH and FSH into the blood. LH has a short half-life (about 20-30 minutes), so its level rises and falls in small waves through the day.
• The ovary is the target. LH acts on the theca cells of a developing follicle to make androgens, which neighbouring cells convert into oestrogen. After ovulation, LH supports the corpus luteum, the structure that makes progesterone in the second half of the cycle.

For most of your cycle, LH sits at a quiet baseline. The drama is concentrated into one short window in the middle. Understanding this shape is the key to using ovulation kits well — and it tracks closely with the hormone shifts across the whole cycle.

• Early to mid follicular phase (roughly days 1-12). LH baseline is low, usually about 2-10 mIU/mL. A dominant follicle is quietly growing and oestrogen is rising in the background. This phase is covered in depth in our follicular phase guide.
• Late follicular phase (around days 12-13). Once oestrogen from the lead follicle reaches a high enough level and stays there, the brain flips from suppressing LH to stimulating it. GnRH pulses speed up and LH starts to climb.
• The LH surge (about 24-36 hours). LH shoots up from baseline to a peak of roughly 25-100 mIU/mL — often a 10-fold jump or more. This surge is the signal that triggers ovulation.
• Ovulation. The egg is usually released about 24-36 hours after the surge begins, or roughly 10-12 hours after the LH peak. The exact gap varies between women and even between cycles — we explain the range in how long after the LH surge you ovulate.
• Luteal phase (days 15-28). LH falls back to baseline. The follicle becomes the corpus luteum, which makes progesterone. If pregnancy does not occur, progesterone drops, the cycle resets, and LH begins to rise for the next month.

Ovulation predictor kits (OPKs) are urine test strips that detect the LH surge — and they are now sold in every chemist and on every Indian pharmacy app. They are the most accessible way at home to predict your fertile window. For a deeper brand-by-brand walkthrough, see our guides to ovulation test kits in India and how ovulation tests work.

The mechanism. The strip contains antibodies that bind LH. When urinary LH crosses a threshold (most kits are set at about 25-40 mIU/mL), the test line darkens. A test is positive when the test line is as dark as or darker than the control line. A faint line means LH is rising but not yet at threshold — keep testing.

When to start. Subtract 17 from your shortest recent cycle length to find the day to begin. For a 26-day cycle, start on day 9; for a 32-day cycle, start around day 15. Knowing your own cycle first makes this far more accurate — see how to track ovulation.

Practical rules that improve accuracy:

• Test once or twice a day. Twice-daily testing (mid-morning and late afternoon) catches short surges that once-daily testing can miss.
• Use afternoon urine (roughly 2 pm to 8 pm), not first-morning urine. Unlike pregnancy tests, OPKs are less reliable on first-morning urine because LH is often lower then.
• Limit fluids for 1-2 hours before testing; very dilute urine can give a false negative.
• Set a timer and read the result exactly when the instructions say.

When LH is measured in blood for a fertility or menstrual workup, it is read in the context of timing in your cycle, your FSH and oestrogen, your age and your symptoms — never in isolation. LH is usually part of a broader fertility hormone panel.

The day 2-3 baseline. The standard timing is days 2-3 of your period, when LH and FSH reflect the unstimulated pituitary. A normal baseline LH is roughly 2-10 mIU/mL, with LH and FSH usually about equal (a 1:1 ratio). The exact reference range depends on the lab's assay and will be printed on your report.

What the result can suggest:

• Raised LH relative to FSH (ratio above 2:1): supports — but does not prove — PCOS.
• High LH and FSH together (both above ~20-25) with low oestrogen: points to the ovary failing to respond — primary ovarian insufficiency if you are under 40, or perimenopause/menopause if older.
• Low LH and FSH together (both very low) with low oestrogen: points to a problem above the ovary, in the hypothalamus or pituitary.

Polycystic ovary syndrome is the most common reason LH gets measured in young women. The pattern is informative — but it is deliberately not a formal diagnostic criterion. If you are new to the condition, start with 5 things every Indian woman should know about PCOS.

The typical PCOS pattern. Many women with PCOS show a raised baseline LH (often 12-25 mIU/mL) with normal-to-low FSH, giving an LH-to-FSH ratio of 2:1 or higher. This happens because GnRH pulses run faster than usual, which preferentially drives LH over FSH. The extra LH pushes the ovary's theca cells to make more androgens — feeding the high testosterone and excess hair growth some women experience — while the relatively low FSH fails to mature a dominant follicle, leading to anovulation.

But not everyone with PCOS has high LH. Only about 60-70% show the classic raised ratio; the rest have a normal ratio, especially in the insulin-resistance-dominant phenotype. That is why diagnosis follows the Rotterdam criteria — at least two of: irregular or absent ovulation, clinical or biochemical hyperandrogenism, and polycystic ovaries on ultrasound — after excluding other causes. LH adds context; it never stands alone.

Why OPKs are tricky in PCOS. Persistently high baseline LH can keep ovulation kits showing positive (or near-positive) for days, with no real ovulation behind it. If you have PCOS and are trying to conceive, BBT charting, cervical mucus tracking and clinic ultrasound monitoring are usually more reliable than OPKs.

Management and LH. Treatments that calm the disordered pattern can normalise LH: combined hormonal contraception suppresses it, weight loss and addressing insulin resistance can lower it, and ovulation-induction drugs like letrozole drive the FSH side to restore ovulation — covered in PCOS fertility treatment. Indian PCOS care (FOGSI and ICMR guidance) also stresses long-term metabolic monitoring, given the high baseline metabolic risk in Indian women. Meta-analyses suggest roughly 9-22% of reproductive-age Indian women have PCOS, depending on criteria and population.

When the ovaries' follicular supply runs low or stops responding, oestrogen falls, the brain loses its 'off' signal, and LH and FSH rise sharply.

Primary ovarian insufficiency (POI). This is loss of ovarian function before age 40, with irregular or absent periods, FSH above about 25 mIU/mL on two occasions, low oestrogen, and usually a raised LH too. It affects about 1-2% of women, with causes including genetic (such as Turner syndrome or fragile X premutation), autoimmune, and treatment-related (chemotherapy, radiation, ovarian surgery); often no cause is found. POI matters well beyond fertility — early oestrogen loss affects bone and heart health, so hormone therapy is usually recommended until around the natural age of menopause. Our POI in India guide covers diagnosis, donor-egg options under the ART Act 2021, and long-term care.

Perimenopause and menopause. In the years before menopause, LH and FSH rise but fluctuate — one cycle's reading can look post-menopausal and the next can look normal. That is why a single hormone test in your 40s means little, and the clinical picture matters more. After menopause (12 months without a period), LH typically settles at 20-100 mIU/mL and stays there. The average age of menopause in Indian women is about 46-50, a little earlier than in Western populations. To understand which stage you are in, see perimenopause vs menopause and what perimenopause is.

A note on age. POI (under 40), early menopause (40-45), and typical perimenopause (late 40s) all share rising LH and FSH — the difference is age and what it means for fertility and hormone-therapy decisions. A gynaecologist will interpret the numbers alongside your history. Ovulation kits are not useful here: post-menopausal LH is permanently above the OPK threshold, so they read positive without any ovulation.

If LH and FSH are low rather than high, the problem usually sits above the ovary — in the hypothalamus or pituitary. This is called hypogonadotropic hypogonadism.

Functional hypothalamic amenorrhoea is the most common version in young women. When the body senses an energy shortfall, it dials down GnRH pulses to conserve resources, so LH and FSH fall, oestrogen drops, and periods stop. Common triggers are low body weight or recent weight loss, very high-intensity exercise (endurance running, gymnastics, ballet, competitive sport), severe stress, and eating disorders. The hormone profile typically shows low LH, low FSH, low oestrogen, with normal prolactin and thyroid hormones. Reassuringly, it is one of the most reversible causes of missed periods: restoring adequate nutrition and easing back on excessive exercise usually brings cycles back over weeks to months, often with input from a gynaecologist, dietitian and, where needed, a mental-health professional. If your periods have simply stopped, our guide to the causes of missed periods is a good starting point.

Pituitary causes include a prolactinoma — a benign pituitary tumour that raises prolactin, which in turn suppresses LH and FSH. This is a quietly common and very treatable cause of missed periods and trouble conceiving; read high prolactin and hyperprolactinaemia in women. Other pituitary problems — non-functioning tumours, damage from surgery or radiation, or Sheehan syndrome after severe postpartum bleeding — can also lower LH.

Congenital causes such as Kallmann syndrome present as delayed or absent puberty and are diagnosed with hormone tests, sometimes genetics, and an MRI. In children and teens, an unusually early LH rise can signal precocious puberty, while persistently low levels at the expected age can mean delayed puberty — both warrant paediatric endocrinology review.

Beyond diagnosis, LH (and its lookalike hCG) is used directly in fertility treatment. Knowing the basics demystifies an IUI or IVF plan.

• Ovulation induction. Oral tablets such as letrozole or clomiphene nudge the pituitary to make FSH and grow a follicle; your own LH surge (or a triggered injection) then releases the egg. This is first-line for conceiving with irregular cycles and PCOS.
• Gonadotropin injections. Recombinant FSH and LH, or human menopausal gonadotropin (which contains both), are injected to grow several follicles in IUI and IVF cycles.
• Preventing a premature surge. GnRH agonists or antagonists are used during IVF to stop an early LH surge from releasing eggs before they can be collected.
• The trigger shot. Once follicles are mature, an hCG (or LH-agonist) injection mimics the natural LH surge to finalise egg maturation and time release or retrieval precisely — usually 34-36 hours before IVF egg pickup.
• Luteal support. After ovulation or embryo transfer, progesterone (and sometimes hCG) supports the womb lining for implantation.

• Track your cycle for 2-3 months first, so you know your typical length and can time when to start testing.
• Test with afternoon urine (about 2 pm to 8 pm), not first-morning urine, and avoid drinking a lot of fluid in the 1-2 hours beforehand.
• For line-based kits, only count it positive when the test line is as dark as or darker than the control line; a faint line means keep testing.
• Combine OPKs with cervical mucus (clear, stretchy, egg-white-like near ovulation) and BBT for a far more reliable picture than any single method.
• After a positive kit, the fertile window is the day of the positive plus the next 1-2 days; sex every other day in this window is as effective as daily.
• Don't over-read a single cycle. A one-off no-surge or double-peak cycle is usually just normal variation; patterns over 2-3 cycles are what matter.
• If you never get a positive across several cycles, or get persistent positives, or have been trying for 6-12 months without success, see a gynaecologist for evaluation.

• You have been trying to conceive for 12 months (or 6 months if you are 35 or older) with well-timed intercourse.
• Your ovulation kits never turn positive across several cycles, or stay positive for many days in a row.
• Your periods are irregular, very infrequent, or have stopped for three months or more.
• You have signs of high androgens — significant acne, excess facial or body hair, or scalp hair thinning — alongside irregular cycles.
• You are under 40 and have menopause-like symptoms (hot flushes, missed periods), which may suggest ovarian insufficiency.
• You have unexplained milky nipple discharge or persistent headaches with missed periods, which can point to a prolactin or pituitary cause.
• A child shows signs of puberty before age 8, or a teenager shows no signs of puberty by age 13-14.

• ACOG — Evaluating Infertility (FAQ)
• NHS — Periods and fertility in the menstrual cycle
• ESHRE — International evidence-based guideline for the assessment and management of PCOS
• ICMR — National Guidelines for Accreditation, Supervision and Regulation of ART Clinics in India
• MedlinePlus — Luteinizing hormone (LH) blood test