A 28-year-old woman with polycystic ovary syndrome (PCOS) presents with primary infertility of 2 years duration. She has regular menstrual cycles after metformin therapy but remains anovulatory on ultrasound. What is the drug of choice for ovulation induction in this patient?

Explanation

## First-Line Ovulation Induction in PCOS **Key Point:** Letrozole (an aromatase inhibitor) is the **drug of choice** for ovulation induction in PCOS-related anovulatory infertility, superseding clomiphene citrate based on landmark RCT evidence and current international guidelines (ASRM/ESHRE 2023, NICE 2023). ### Mechanism of Action Letrozole works by: 1. Inhibiting aromatase enzyme → reduces peripheral estrogen synthesis 2. Removes negative estrogen feedback at the hypothalamus/pituitary → increases endogenous FSH 3. Promotes mono-follicular development (lower multiple pregnancy risk vs. CC) 4. Does NOT deplete endometrial/cervical estrogen receptors (unlike CC) → better endometrial receptivity ### Landmark Evidence The **Legro et al. NEJM 2014** RCT (n = 750 PCOS women) demonstrated: - **Live birth rate:** Letrozole **27.5%** vs. Clomiphene **19.1%** (p = 0.007) - **Ovulation rate:** Letrozole **61.7%** vs. Clomiphene **48.3%** - **Multiple pregnancy rate:** Letrozole **3.4%** vs. Clomiphene **7.4%** ### Comparative Overview | Feature | Letrozole | Clomiphene Citrate | Gonadotropins | |---------|-----------|-------------------|---------------| | **Current first-line status** | ✅ Yes (ASRM 2023) | ❌ No longer first-line | Second-line | | **Route** | Oral | Oral | Injectable | | **Live birth rate (PCOS)** | Higher (~27–30%) | Lower (~19–22%) | High but OHSS risk | | **Multiple pregnancy risk** | Low (~3%) | Moderate (~7%) | High (5–10%) | | **Endometrial receptivity** | Preserved | Reduced (anti-estrogenic) | Preserved | | **OHSS risk** | <1% | 1–2% | 5–10% | ### Dosing Protocol - **Starting dose:** 2.5 mg daily × 5 days (cycle days 3–7) - **Escalation:** 5 mg → 7.5 mg if no ovulation - **Monitoring:** Transvaginal ultrasound day 12–14 ### Escalation Pathway in PCOS 1. **First-line:** Letrozole (± metformin in insulin-resistant PCOS) 2. **Second-line:** Gonadotropins (low-dose step-up protocol) or Laparoscopic Ovarian Drilling (LOD) 3. **Third-line:** IVF/ICSI **Clinical Pearl:** Clomiphene citrate was historically the gold standard but has been displaced by letrozole in current guidelines due to superior live birth rates and a more favorable safety profile. Approximately 20–25% of PCOS patients are clomiphene-resistant, further reinforcing letrozole as the preferred first-line agent. For NEET PG/INI-CET purposes, **letrozole is the current drug of choice** for ovulation induction in PCOS. ### Why Other Options Are Incorrect - **GnRH agonist (A):** Used for pituitary downregulation in ART protocols, NOT for ovulation induction in PCOS - **Gonadotropins (B):** Second-line; high OHSS risk, expensive, requires intensive monitoring - **Clomiphene citrate (D):** Previously first-line; now second-line per ASRM/ESHRE 2023 due to inferior live birth rates and anti-estrogenic endometrial effects *Reference: Legro RS et al., NEJM 2014; ASRM Practice Committee 2023; Williams Gynecology 4th ed.*