## First-Line Ovulation Induction in PCOD **Key Point:** Letrozole (an aromatase inhibitor) is now the **drug of choice** for ovulation induction in PCOD-related infertility, superseding clomiphene citrate based on superior live birth rates demonstrated in landmark trials. ### Mechanism of Action Letrozole is a third-generation aromatase inhibitor that: 1. Blocks conversion of androgens to estrogens, transiently lowering circulating estrogen 2. Removes negative feedback on the hypothalamic-pituitary axis → increased FSH secretion 3. Stimulates mono-follicular development, reducing multiple pregnancy risk 4. Does NOT deplete endometrial or cervical mucus estrogen receptors (unlike clomiphene) ### Evidence Base - **Legro et al. (NEJM, 2014):** In the landmark PPCOS II RCT, letrozole produced significantly higher live birth rates (27.5% vs 19.1%) and ovulation rates compared to clomiphene citrate in PCOS patients. - **ESHRE/ASRM 2023 International Evidence-Based Guideline for PCOS** recommends letrozole as **first-line pharmacological ovulation induction** in PCOS. - Multiple meta-analyses confirm letrozole's superiority in live birth rates and comparable or lower multiple pregnancy rates. ### Dosing & Protocol - **Starting dose:** 2.5 mg daily for 5 days (days 2–6 of cycle) - **Escalation:** Increase by 2.5 mg increments in subsequent cycles if anovulation persists (max 7.5 mg/day) - **Ovulation rate:** ~60–80% in PCOD; live birth rate superior to clomiphene ### Why Letrozole is Now First-Line - Superior live birth rates over clomiphene in PCOS (NEJM 2014) - Better endometrial receptivity (no anti-estrogenic effect on endometrium) - Lower risk of multiple gestation - Shorter half-life → less systemic anti-estrogenic side effects - Endorsed by ESHRE, ASRM, and increasingly by Indian OBG guidelines ### Comparison with Alternatives | Agent | Role in PCOD | When Used | |-------|--------------|-----------| | **Letrozole** | **First-line ovulation induction** | All PCOD patients desiring fertility | | **Clomiphene citrate** | Second-line / historical first-line | Where letrozole unavailable; still used in some curricula | | **Metformin** | Adjunct; improves insulin sensitivity | Obese PCOD; cycle regularization; combined with letrozole | | **Spironolactone** | Anti-androgen; treats hirsutism | Cosmetic concerns; does NOT induce ovulation | **High-Yield:** The NEJM 2014 (Legro et al.) trial is the pivotal study establishing letrozole's superiority. ESHRE/ASRM 2023 guidelines formally recommend letrozole as first-line. Clomiphene citrate was the historical gold standard but has been displaced by letrozole in current evidence-based practice. **Clinical Pearl:** Spironolactone treats hirsutism but is **teratogenic** and must NOT be used in women desiring pregnancy. Metformin alone has poor ovulation induction efficacy compared to letrozole. Gonadotropins are reserved for letrozole/clomiphene failure. ### Monitoring During Treatment - Transvaginal ultrasound on day 10–12 to assess follicular development - Serum progesterone >3 ng/mL on day 21 confirms ovulation - If no ovulation after 3 cycles at maximum dose, escalate to gonadotropins or consider laparoscopic ovarian drilling
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