What is the recommended evaluation and workup for a patient with oligomenorrhea?

Oligomenorrhea Workup

Begin with a pregnancy test, followed by measurement of FSH, LH, TSH, and prolactin levels, with additional testosterone assessment if clinical hyperandrogenism is present, and pelvic ultrasound when hormonal tests or clinical features suggest ovarian pathology. 1

Initial Clinical Assessment

Document the following specific details:

• Menstrual history: Age of menarche, cycle regularity, duration of oligomenorrhea (cycles >35 days), and pattern of irregularity 1
• Weight and nutritional assessment: Recent weight changes, eating patterns, BMI calculation, and signs of disordered eating 1
• Exercise habits: Hours per week and intensity of physical activity, particularly >10 hours/week of intense training 2
• Medication review: Current use of hormonal contraceptives, antipsychotics, antiepileptics, or other medications that can cause menstrual irregularities 1
• Hyperandrogenic symptoms: Presence of hirsutism, acne, androgenetic alopecia, or truncal obesity 3, 4
• Galactorrhea: Suggests hyperprolactinemia and potential pituitary pathology 1, 2

Mandatory Laboratory Testing

Order these tests in all patients with oligomenorrhea:

• Pregnancy test (urine or serum β-hCG): Must be performed first to exclude pregnancy before other hormonal testing 1, 4
• FSH and LH: Draw between cycle days 3-6 if cycles are present, or at any time in amenorrheic patients; LH/FSH ratio >2 suggests PCOS, while ratio <1 suggests functional hypothalamic amenorrhea 1, 4
• TSH: Identifies thyroid dysfunction as a reversible cause of oligomenorrhea 1, 4
• Prolactin: Elevated levels (>20 μg/L) suggest hyperprolactinemia, which may indicate pituitary adenoma or medication effect 1

Add these tests based on clinical presentation:

• Total and free testosterone: When clinical signs of hyperandrogenism are present (hirsutism, acne); testosterone >2.5 nmol/L suggests PCOS 1, 4
• Estradiol: When functional hypothalamic amenorrhea is suspected; low levels indicate hypoestrogenism 1, 2
• Mid-luteal progesterone (day 21-23): To determine ovulatory status; levels <6 nmol/L indicate anovulation 1

Imaging Studies

Pelvic ultrasound is indicated when:

• Clinical features or hormonal tests suggest PCOS (>10 peripheral cysts with thickened ovarian stroma) 1, 4
• Structural abnormalities are suspected 1
• Assessment of endometrial thickness is needed (thin endometrium <5 mm suggests estrogen deficiency; thick endometrium >8 mm suggests chronic anovulation with unopposed estrogen) 1, 2

Transvaginal ultrasound is more sensitive than transabdominal for identifying structural abnormalities. 1

Interpretation Algorithm by Hormone Pattern

Elevated FSH (>40 mIU/mL):

• Indicates primary ovarian insufficiency; confirm with repeat FSH 4 weeks later (two elevated values required for diagnosis) 1
• Consider karyotype testing if age <40 years to identify Turner syndrome 1

Low FSH with low estradiol:

• Suggests functional hypothalamic amenorrhea (FHA); evaluate for eating disorders, excessive exercise, psychological stress, and low bone density 1, 2
• LH/FSH ratio <1 seen in approximately 82% of FHA cases 1

LH/FSH ratio >2 with normal/elevated testosterone:

• Strongly suggests PCOS; 51% of anovulatory oligomenorrhea cases 4, 5
• Assess for metabolic syndrome risk factors (glucose intolerance, dyslipidemia) 6

Elevated prolactin:

• Suggests hyperprolactinemia (20% of secondary amenorrhea cases); consider pituitary adenoma or medication effect 2
• Obtain MRI if prolactin significantly elevated or neurological symptoms present 1

Elevated TSH:

• Indicates hypothyroidism as reversible cause 1, 4

Additional Testing for Specific Scenarios

For thin or athletic patients with oligomenorrhea:

• Calculate energy availability (>30 kcal/kg fat-free mass/day) 2
• Screen for Female Athlete Triad with DXA scan for bone mineral density if amenorrhea >6 months 1, 2

For patients with signs of hyperandrogenism:

• Add androstenedione and DHEA-S to evaluate for adrenal/ovarian tumors or non-classical congenital adrenal hyperplasia 3, 4

Critical Pitfalls to Avoid

• Do not measure hormones while patient is on hormonal contraception, as this affects accuracy 4
• Do not assume amenorrhea in athletes is benign; other pathology must be excluded even when clinical picture suggests FHA 2
• Do not rely on single FSH measurements, as levels fluctuate significantly; timing during menstrual cycle is crucial 4
• Do not overlook eating disorders; adolescents frequently minimize or deny disordered eating behaviors, requiring direct questioning about specific behaviors 2
• Do not delay bone density assessment; DXA scanning is indicated regardless of age if amenorrhea extends beyond 6 months 2

When to Refer to Specialist

Refer to endocrinology or gynecology for:

• Persistent oligomenorrhea >6 months despite initial evaluation 4
• Abnormal hormone levels suggesting specific pathology (elevated FSH, significantly elevated prolactin) 2, 4
• Signs of hyperandrogenism with menstrual irregularity 4
• Infertility concerns 4
• Suspected structural abnormalities on imaging 4
• Signs of eating disorder requiring multidisciplinary team 2