Letrozole Use in Polycystic Ovary Syndrome: Eligibility, Contraindications, and Monitoring

Eligibility Criteria

Patients must be confirmed non‑pregnant by clinical criteria (e.g., within 7 days of menses onset or no intercourse since last menses) or a urine pregnancy test before initiating letrozole therapy. 1
Letrozole may be used in post‑pubertal individuals when gonadotoxic treatment has delayed ovulation. 2

Breastfeeding ≤ 21 days postpartum is an absolute contraindication to letrozole because of potential fetal harm. 1

Age ≥ 35 years combined with smoking ≥ 15 cigarettes per day precludes letrozole use. 1
Systolic blood pressure ≥ 160 mm Hg or diastolic blood pressure ≥ 100 mm Hg is an absolute contraindication. 1
Presence of any vascular disease (e.g., peripheral arterial disease, coronary artery disease) excludes letrozole therapy. 1
Acute venous thromboembolism (VTE) or a history of VTE with at least one recurrence risk factor (e.g., thrombophilia) contraindicates letrozole. 1
Recent major surgery requiring prolonged immobilization is an absolute contraindication. 1
Known thrombogenic genetic mutations (e.g., Factor V Leiden, prothrombin G20210A, protein S/C deficiency, antithrombin deficiency) preclude use. 1
Current or prior ischemic heart disease or stroke makes letrozole use unsafe. 1
Multiple risk factors for atherosclerosis (e.g., hypertension, hyperlipidaemia, diabetes) constitute an absolute contraindication. 1

Acute viral hepatitis flare, severe or decompensated cirrhosis, and hepatocellular adenoma or malignant liver tumor are absolute contraindications. 1

Active breast cancer is an absolute contraindication. 1
Migraine with aura excludes letrozole therapy. 1
Diabetes with end‑organ complications (nephropathy, retinopathy, neuropathy) or disease duration ≥ 20 years is an absolute contraindication. 1
Systemic lupus erythematosus with positive or unknown antiphospholipid antibodies contraindicates letrozole. 1

Age ≥ 35 years with smoking < 15 cigarettes per day is a relative contraindication; benefits must outweigh risks. 1
Systolic blood pressure 140–159 mm Hg or diastolic blood pressure 90–99 mm Hg is a relative contraindication. 1
Adequately controlled hypertension may be tolerated but requires careful monitoring. 1
History of VTE without additional recurrence risk factors is a relative contraindication. 1
Superficial venous thrombosis is a relative contraindication. 1
Prior breast cancer in remission for ≥ 5 years may be considered with caution. 1
Breastfeeding between 21–42 days postpartum combined with VTE risk factors is a relative contraindication. 1

When combined with standard fertility drugs, letrozole maintains estrogen levels near physiologic ranges, making it suitable for patients with estrogen‑sensitive conditions. 3
Short‑term follow‑up shows no adverse effect on cancer‑free survival when letrozole is used for fertility preservation. 3

Blood pressure must be measured before initiating letrozole therapy to identify hypertension or contraindicating values. 1

Letrozole should not be prescribed to premenopausal women outside clinical trials for breast cancer treatment. 4
Women rendered amenorrheic by chemotherapy may continue ovarian estrogen production despite absent menses; therefore, hormonal assessment is essential. 4
Serial measurement of luteinising hormone, follicle‑stimulating hormone, and estradiol is mandatory to confirm true postmenopausal status before considering letrozole for breast cancer. 4

The American College of Obstetricians and Gynecologists recommends that all women with PCOS attempting pregnancy must begin with lifestyle modifications targeting 5-10% weight loss through diet and exercise, with an energy deficit of 500-750 kcal/day and total intake of 1,200-1,500 kcal/day 5, 6
Modest weight loss of just 5% of initial body weight significantly improves ovulation and pregnancy rates in women with PCOS 6
Women with PCOS should perform at least 250 minutes/week of moderate-intensity activity for weight loss, plus muscle strengthening on 2 non-consecutive days/week 5
The Endocrine Society recommends that women should have BMI ≥18.5 kg/m² before ovulation induction is offered 7

The American College of Obstetricians and Gynecologists recommends that all women with PCOS must undergo metabolic screening, including fasting glucose and 2-hour glucose tolerance test, lipid profile, and ensure BMI ≥18.5 kg/m² before initiating any fertility treatment 6, 7
Preconception counseling should include information about increased pregnancy risks, including preeclampsia, gestational diabetes, and pregnancy loss, and plan for closer monitoring throughout pregnancy 6
The American Heart Association recommends prescribing low-dose aspirin from week 12 to week 36 to reduce preeclampsia risk in women with PCOS 6

The European Society of Human Reproduction and Embryology recommends avoiding the use of clomiphene citrate as first-line treatment in functional hypothalamic amenorrhea (FHA) - it is ineffective and not recommended 8, 7
The American Society for Reproductive Medicine recommends not exceeding recommended clomiphene dosage (150 mg/day) or duration (6 cycles total) 5
The Endocrine Society recommends not neglecting metabolic screening even in normal-weight PCOS patients 5
The American College of Obstetricians and Gynecologists recommends not initiating ovulation induction in women with BMI <18.5 kg/m² 7