Polycystic ovary syndrome is the most common cause of anovulatory infertility, accounting for roughly 70–80% of cases where irregular or absent ovulation is the primary barrier to conception (Thessaloniki ESHRE/ASRM Consensus 2008). But PCOS is also one of the most treatable causes of infertility — the right workup and the right approach get most PCOS patients pregnant.
This guide covers what PCOS does to fertility at a hormonal level, what labs to request and how to interpret them, when to start a clinical workup, and what ovulation induction involves — including updated Monash 2023 guidance that changed the first-line medication recommendation.
How PCOS disrupts ovulation
The core problem in PCOS is a disruption of the normal LH-FSH pulsatility that drives follicular development. In a typical cycle, FSH rises in the early follicular phase, a dominant follicle develops and produces rising estrogen, the estrogen surge triggers an LH surge, and ovulation occurs.
In PCOS, several overlapping abnormalities interfere with this sequence:
- Elevated LH relative to FSH. LH pulses are more frequent and larger in amplitude. FSH pulses are relatively suppressed. This drives androgen production from the theca cells of developing follicles but does not provide enough FSH to push a single follicle to dominance.
- Follicular arrest. Multiple small follicles (2–9 mm) develop but none reaches the 18–20 mm diameter needed for the LH surge to trigger ovulation. These arrested follicles are the “polycystic” appearance on ultrasound — defined by the 2023 Monash criteria as 20 or more follicles per ovary or an ovarian volume over 10 mL on a transvaginal ultrasound using modern technology.
- Insulin resistance and hyperinsulinemia. Present in approximately 70% of women with PCOS regardless of body weight (Dunaif, NEJM 1997). Elevated insulin stimulates ovarian theca cell androgen production and suppresses sex-hormone-binding globulin (SHBG), increasing free androgen levels. High androgens reinforce follicular arrest.
- Elevated anti-Mullerian hormone (AMH). Produced by the excess small follicles, AMH suppresses FSH sensitivity and further impairs follicular maturation.
The result: cycles that may never produce ovulation, or that ovulate unpredictably after prolonged follicular phases.
The hormonal workup: what to measure and why
If you have irregular cycles and are trying to conceive — or if you have been tracking and see evidence of anovulation — the following labs are appropriate to request. Most reproductive endocrinologists will run this panel at the initial consultation; some general gynecologists will run it on request.
LH and FSH
In PCOS, LH is typically elevated relative to FSH, producing an LH:FSH ratio above 2:1. However, this ratio is not required for diagnosis (it has been removed from the Rotterdam and Monash diagnostic criteria) and is not perfectly reliable — it fluctuates across the cycle. Draw both in the early follicular phase (days 2–5 of a cycle, or any time if cycles are very irregular).
AMH
AMH does not vary significantly across the cycle and can be drawn at any time. Elevated AMH (typically above 3.4–5.0 ng/mL depending on lab and reference range) in the context of irregular cycles is consistent with PCOS. Very high AMH (above 7–10 ng/mL) predicts high OHSS risk during IVF and will influence stimulation protocols.
Total testosterone and DHEA-S
Elevated androgens are one of the three Rotterdam diagnostic criteria for PCOS. Measure total testosterone (and free testosterone if available) and DHEA-S (adrenal androgen). Mildly elevated testosterone with normal DHEA-S points toward ovarian androgen excess (typical of PCOS); significantly elevated DHEA-S suggests adrenal involvement and warrants additional workup.
Fasting insulin and glucose
Insulin resistance testing. Some practices run a fasting glucose-to-insulin ratio or HOMA-IR. Formal oral glucose tolerance testing may be recommended if fasting values suggest impaired glucose tolerance. The Monash 2023 guidelines recommend offering testing for type 2 diabetes in all PCOS patients.
Prolactin and TSH
Both hyperprolactinemia and thyroid dysfunction can produce irregular cycles and anovulation that mimics PCOS. These should be ruled out before attributing everything to PCOS. Low thyroid function is particularly common in reproductive-age women.
Pelvic ultrasound
Transvaginal ultrasound to assess ovarian morphology (follicle count and ovarian volume), endometrial thickness (chronic anovulation can produce a thickened or irregular endometrium), and to rule out structural abnormalities. Should be timed to early follicular phase if possible, and performed by a sonographer with experience in reproductive ultrasound.
When to start a clinical workup
Standard guidance says 12 months of trying (under 35) or 6 months (35 and older) before seeking a fertility evaluation. This applies to couples with normal cycles.
For PCOS patients with documented anovulation, waiting 12 months of anovulatory cycles is not useful — you can confirm you are not ovulating in three months of BBT charting, and months 3 through 12 do not add information. The Monash 2023 guidelines state that a referral to a fertility specialist is appropriate when anovulation is established, without requiring the standard 12-month wait.
Practical triggers for earlier evaluation:
- BBT charts with no thermal shift for three consecutive cycles
- Cycles consistently longer than 35 days
- Fewer than 6 periods in the past year
- Known PCOS diagnosis plus any period of trying for 3+ months
The Ovulation Calculator can help you track when ovulation is expected, and charting BBT alongside it will build the evidence base you need.
Lifestyle factors that can restore ovulation
Before medication is considered, lifestyle interventions are first-line for PCOS patients who are overweight or have insulin resistance — and are often helpful even for lean PCOS patients.
Weight and ovulation
Weight loss of 5–10% of body weight in PCOS patients with overweight or obesity is associated with ovulation restoration in a significant proportion of cases (Kiddy et al., Clin Endocrinol 1992; Clark et al., Hum Reprod 1998). The mechanism is reduced insulin resistance, reduced androgen levels, and improved LH-FSH balance. Even without reaching a “normal” BMI, modest weight change can shift hormonal milieu enough to allow follicular development to complete.
This relationship is real but often overstated in clinical settings. Weight loss restores ovulation in some PCOS patients and not others; it is not a guaranteed intervention, and framing it as such can be harmful. The Monash 2023 guidelines recommend lifestyle interventions as first-line treatment but emphasize that pharmacological treatment should not be withheld when lifestyle interventions have not restored ovulation within a reasonable timeframe.
Exercise
Regular moderate-intensity exercise improves insulin sensitivity and may improve cycle regularity in PCOS. The caveat: excessive exercise can suppress ovulation through the same hypothalamic mechanisms that cause hypothalamic amenorrhea — essentially the opposite problem. Aim for 150+ minutes of moderate activity per week, not twice-daily training.
Diet
No single diet has been proven superior for PCOS. A diet that supports insulin sensitivity — lower glycemic load, adequate protein, minimal highly processed carbohydrates — is a reasonable evidence-based approach. The Mediterranean pattern has some supporting evidence for PCOS outcomes.
Ovulation induction: letrozole vs. clomiphene
When lifestyle interventions have not restored ovulation after 3–6 months of effort, ovulation induction with medication is the next step.
Letrozole (first-line, per Monash 2023 and ASRM)
Letrozole is an aromatase inhibitor that temporarily reduces estrogen production. The pituitary responds by releasing more FSH, which stimulates follicle development. Letrozole is taken orally, typically days 2–5 of the cycle (or a progestin-induced withdrawal bleed cycle), for 5 days.
Why letrozole is preferred over clomiphene:
- Higher live birth rates. The landmark Legro et al. (NEJM 2014) randomized controlled trial of 750 women with PCOS found letrozole produced significantly higher cumulative live birth rates than clomiphene (27.5% vs. 19.1% over 5 treatment cycles).
- Lower multiple pregnancy risk. Letrozole acts on the follicular phase and is metabolized before implantation; it does not have the anti-estrogenic effect on the endometrium that clomiphene does. Multiple pregnancy rates with letrozole are approximately 3.4% vs. 7.4% for clomiphene.
- Better endometrial receptivity. Clomiphene’s anti-estrogenic properties thin the endometrial lining in some patients, reducing implantation rates. Letrozole does not have this effect.
The starting dose of letrozole is typically 2.5 mg/day for 5 days; dose can be escalated to 5 mg or 7.5 mg in subsequent cycles if ovulation does not occur.
Clomiphene (clomid): second-line
Clomiphene has been used since the 1960s and remains effective, but is now second-line based on Legro et al. 2014 and subsequent meta-analyses. It works by blocking estrogen receptors at the pituitary, tricking the brain into producing more FSH. Dose typically starts at 50 mg/day for 5 days.
Reasons clomiphene may still be used: availability, lower cost, provider familiarity. It is still effective — roughly 60–85% of PCOS patients on an adequate dose will ovulate, and cumulative pregnancy rates over 6 cycles approach 50–60%.
Monitoring during ovulation induction
Ovulation induction cycles should be monitored with transvaginal ultrasound to confirm follicular development and trigger timing (or natural ovulation), and in some cases a serum LH or hCG trigger injection is used. This allows identification of ovarian hyperstimulation (multiple large follicles, increasing OHSS risk) and timing of intercourse or intrauterine insemination (IUI).
Metformin
Metformin improves insulin sensitivity and has modest effects on cycle regularity and ovulation in PCOS. Monash 2023 and ASRM guidance does not recommend metformin as first-line ovulation induction monotherapy — letrozole is significantly more effective. Metformin may be used adjunctively with letrozole in patients with significant insulin resistance, or in those who cannot tolerate ovulation induction for other reasons.
When ovulation induction does not work: next steps
If 3–6 cycles of letrozole do not produce ovulation or conception, the usual next steps are:
- Adding gonadotropins (FSH injections): More potent stimulation; higher multiple pregnancy risk; requires more intensive monitoring.
- IVF: The most effective intervention for PCOS-related infertility; allows precise control of stimulation and single-embryo transfer to minimize multiple pregnancy.
- Weight management intensification: If insulin resistance is significant and has not been fully addressed.
- Re-evaluation of diagnosis: Ensure there are no additional factors (tubal, male factor, endometriosis) that have not been assessed.
A practical timeline for PCOS fertility care
| Situation | Recommended action |
|---|---|
| PCOS diagnosis, not yet trying | Start cycle tracking (BBT, LH, cycle length) |
| Trying 3+ months with confirmed anovulation | Reproductive endocrinology referral |
| First RE visit | Labs (LH, FSH, AMH, testosterone, insulin, TSH, prolactin), pelvic ultrasound |
| Anovulation confirmed, lifestyle trial 3 months | Letrozole ovulation induction, monitored cycles |
| 3–6 letrozole cycles, no conception | Gonadotropin IUI or IVF evaluation |
The bottom line
PCOS affects fertility primarily through anovulation — but anovulation is treatable. The pathway forward is: confirm anovulation with BBT charting (using the Ovulation Calculator for baseline estimates), get appropriate labs, and pursue ovulation induction with letrozole as first-line when lifestyle changes alone are insufficient. Monash 2023 and ASRM 2024 guidelines are clear that letrozole beats clomiphene on live birth rates, and that waiting passively through confirmed anovulatory cycles is not a useful strategy.
For the cycle-tracking piece, see the PCOS cycle tracking guide. For the anovulation recognition piece, see the anovulation guide.