How to diagnose an anovulatory cycle in a woman with Polycystic Ovary Syndrome (PCOS)?

Assessing Anovulatory Cycles in Women with PCOS

Measure mid-luteal phase serum progesterone levels—a value <6 nmol/L confirms anovulation in women with PCOS. 1

Primary Diagnostic Method

The most reliable way to assess anovulation in PCOS is through serum progesterone measurement during the mid-luteal phase of the menstrual cycle. 1 This test should be performed approximately 7 days before expected menstruation (typically cycle day 21 in a 28-day cycle, adjusted for cycle length). 1

Interpretation of Progesterone Levels

• <6 nmol/L: Indicates anovulation 1
• Normal levels: Suggest ovulatory cycles despite PCOS diagnosis 1

This single test is the most direct biochemical marker because progesterone is only produced in significant amounts by the corpus luteum after ovulation occurs. 1

Supporting Clinical Assessment

Menstrual Pattern Documentation

Track menstrual cycles for at least 6 months using a menstrual chart to identify: 1

• Oligomenorrhea: Cycles >35 days 1
• Amenorrhea: No bleeding for >6 months 1
• Polymenorrhea: Cycles <23 days 1

Cycle length >35 days strongly suggests chronic anovulation, while cycles of 32-35 days require progesterone testing to confirm ovulatory status. 2

Basal Body Temperature Charting

While less reliable than progesterone testing, basal body temperature graphs can provide supportive evidence. 3 Anovulatory cycles typically show a monophasic pattern without the characteristic temperature rise that occurs after ovulation. 3

Hormonal Profile to Confirm PCOS-Related Anovulation

When anovulation is confirmed, obtain these hormone levels on days 3-6 of the cycle to characterize the underlying pathophysiology: 1

• LH/FSH ratio >2: Characteristic of PCOS 1
• Testosterone >2.5 nmol/L: Confirms hyperandrogenism 1
• Prolactin levels: Rule out hyperprolactinemia as alternative cause 1
• TSH: Exclude thyroid dysfunction 1

Ultrasound Findings

Pelvic ultrasound (preferably transvaginal) performed on cycle days 3-9 can support the diagnosis but is not required to confirm anovulation itself. 1 Look for: 1

• ≥25 follicles (2-9 mm diameter) in at least one ovary 1, 4
• Ovarian volume ≥10 mL 1, 4
• Thickened ovarian stroma 1

Important caveat: Polycystic ovarian morphology appears in up to one-third of reproductive-aged women without PCOS, so ultrasound findings alone cannot diagnose anovulation. 1

Metabolic Screening

Since anovulatory PCOS carries metabolic risks, simultaneously assess: 1

• Fasting glucose followed by 2-hour oral glucose tolerance test (75-gram load) to screen for diabetes 1
• Fasting lipid profile: Total cholesterol, LDL, HDL, triglycerides 1
• Fasting glucose/insulin ratio >4: Suggests insulin resistance 1

Common Pitfalls to Avoid

1. Timing error: Progesterone must be measured mid-luteal phase, not randomly during the cycle—incorrect timing yields false results 1

2. Single abnormal finding: One low progesterone level without clinical context (irregular cycles) may not represent chronic anovulation—repeat testing is warranted 1

3. Confusing polycystic ovaries with PCOS: Ultrasound findings of polycystic ovaries without anovulation or hyperandrogenism do not constitute PCOS 1

4. Missing alternative diagnoses: Always exclude hyperprolactinemia, thyroid disease, Cushing's syndrome, and androgen-secreting tumors before attributing anovulation solely to PCOS 1

Clinical Significance

Confirming anovulation in PCOS is critical because chronic anovulation increases risk of: 1

• Endometrial hyperplasia and cancer (from unopposed estrogen) 1, 5
• Infertility 1
• Metabolic complications including type 2 diabetes 1, 6

Women with confirmed anovulatory PCOS require endometrial protection through combined oral contraceptives or cyclic progestins if not attempting pregnancy. 1, 5