🧬 PCOS Fertility & Ovulation Induction Simulator

Anovulatory PCOS — Follicles Arrest, No Egg Released

Polycystic ovaries hold many small follicles that never mature.

• 6–13%: PCOS prevalence (reproductive-age women)
• 70–80%: Anovulatory infertility share (of PCOS infertility cases)
• 12+: Antral follicle count (small, arrested follicles)
• ~2–3:1: LH:FSH ratio (elevated and skewed)

Follicular arrest

Small follicles stall before reaching a dominant size.

Chronic anovulation blocks the LH surge needed to trigger ovulation.

Hormonal imbalance

Excess androgens and insulin resistance disrupt normal signaling.

Why induction is needed

Ovulation induction restarts the hypothalamic-pituitary-ovarian axis pharmacologically.

Letrozole Blocks Estrogen Synthesis At The Ovary

Letrozole halts aromatase, cutting estrogen production directly at the follicle.

• >97%: Aromatase inhibition (enzyme activity suppressed)
• ↓60–80%: Estrogen drop (circulating estradiol falls)
• ↑40–60%: FSH rise (reduced negative feedback)
• ~45 h: Half-life (short-acting, self-limiting)

Aromatase enzyme

Granulosa cells can no longer convert androgens into estrogen.

Blocking the ovary itself keeps brain estrogen receptors untouched.

Central feedback

Low estrogen removes the brake on hypothalamic GnRH pulses.

Monofollicular tendency

Local androgen buildup favors selecting a single follicle.

Clomiphene Blocks Estrogen Receptors In The Brain

Clomiphene occupies hypothalamic receptors, tricking the brain into low-estrogen mode.

• Weeks: Receptor occupancy (long receptor dwell time)
• ↑50–70%: FSH rise (centrally driven surge)
• Central: Antiestrogenic site (hypothalamus and pituitary)
• 5–7 d: Half-life (longer systemic exposure)

Selective estrogen receptor modulator

Clomiphene competitively blocks estrogen from binding its receptor.

The brain misreads normal estrogen as deficient, boosting FSH output.

Peripheral anti-estrogen effects

Blocked receptors also thin the endometrium and cervical mucus.

Multifollicular tendency

Weaker follicle selection lets several follicles grow together.

Rising FSH Recruits And Grows Ovarian Follicles

Circulating FSH binds granulosa cells, driving follicles toward maturity.

• ~2 d: FSH threshold window (recruitment sensitivity period)
• ~2 mm/d: Follicle growth rate (during stimulation)
• 18–24 mm: Mature follicle size (triggers ovulation readiness)
• US scan: Monitoring method (tracks follicle count/size)

FSH threshold

Only follicles above the FSH threshold keep growing.

Higher dose widens the threshold window, recruiting more follicles.

Granulosa proliferation

FSH drives granulosa cell division and estrogen output.

Dose-dependent recruitment

Standard and high doses raise follicle count and multiples risk.

Comparing Ovulation Rate And Multiple-Pregnancy Risk

An LH surge triggers release of one or more mature eggs.

• 61.7%: Letrozole ovulation rate (per treatment cycle)
• 48.3%: Clomiphene ovulation rate (per treatment cycle)
• 3.4%: Letrozole multiples rate (twin pregnancy risk)
• 7.4%: Clomiphene multiples rate (twin pregnancy risk)

LH surge

A sharp LH spike ruptures the dominant follicle wall.

Letrozole favors single-egg ovulation, lowering multiple-birth risk substantially.

Live birth outcomes

Letrozole shows higher live birth rates in PCOS trials.

Clinical guideline

Major guidelines now recommend letrozole as first-line therapy.