The Progesterone Problem: Why Under-Ovulation Is the Key to Understanding Hormonal Deficiency in PCOS

The Forgotten Hormone in PCOS

When people talk about Polycystic Ovary Syndrome (PCOS), the spotlight usually shines on androgens like testosterone or estrogens like estradiol. But one critical hormone often gets left out of the conversation: progesterone.

Progesterone is only made in significant amounts after ovulation. And here’s the catch—most women with PCOS ovulate irregularly, or sometimes not at all. That means many live in a constant state of progesterone deficiency, which disrupts cycles, worsens estrogen imbalance, and increases long-term health risks.

What Progesterone Does for the Body

Progesterone is more than just a fertility hormone—it’s a regulator and protector.

• Balances estrogen: Keeps estradiol and estrone in check, preventing overstimulation of the uterine lining.
  
  

• Supports pregnancy: Prepares the uterine lining for implantation and maintains early pregnancy.
  
  

• Calms the nervous system: Acts on brain receptors to promote relaxation, reduce anxiety, and improve sleep.
  
  

• Protects the uterus: Prevents abnormal cell growth by counterbalancing estrogen’s effects.
  
  

• Influences metabolism: Plays a role in insulin sensitivity and fat storage.
  
  

Without enough progesterone, women are left vulnerable to both reproductive and systemic complications.

Why Women with PCOS Don’t Make Enough Progesterone

1. Irregular or absent ovulation (anovulation):
   
   

   • In PCOS, the LH-to-FSH imbalance makes it hard for ovarian follicles to fully mature.
     
     

   • Without a dominant follicle, ovulation often doesn’t occur.
     
     

   • No ovulation = no corpus luteum = no progesterone.
     
     

2. Low-frequency ovulation (oligo-ovulation):
   
   

   • Even when ovulation happens, it may be sporadic—leaving progesterone levels unstable.
     
     

3. Imbalanced hormone signaling:
   
   

   • Excess insulin and androgens disrupt normal ovarian signaling, further suppressing ovulation.
     
     

The Ripple Effect of Progesterone Deficiency in PCOS

• Cycle irregularities: Long, unpredictable cycles or skipped periods.
  
  

• Endometrial risk: Without progesterone to counter estrogen, the uterine lining can thicken abnormally, raising the risk of endometrial hyperplasia or even cancer over time.
  
  

• Fertility challenges: Without consistent ovulation and progesterone, sustaining pregnancy is more difficult.
  
  

• Mood and sleep problems: Low progesterone can worsen anxiety, depression, and insomnia.
  
  

• Metabolic dysfunction: Progesterone deficiency contributes to insulin resistance and systemic inflammation.
  
  

How Progesterone Deficiency Interacts with Estradiol and Estrone

Progesterone deficiency doesn’t occur in isolation—it amplifies the estrogen imbalance already present in PCOS.

• Too little estradiol (E2): Leaves the body without protective effects for bone, brain, and metabolism.
  
  

• Too much estrone (E1): Fuels inflammation and overstimulates estrogen receptors.
  
  

• Not enough progesterone: Removes the natural “brake system” that keeps estrone in check.
  
  

This triple imbalance is what makes PCOS so complex—and why buzzwords like “estrogen dominance” miss the point entirely.

What Women Can Do to Support Progesterone Health

1. Track ovulation: Use basal body temperature, ovulation predictor kits, or lab testing (mid-luteal progesterone).
   
   

2. Improve insulin sensitivity: Lowering insulin resistance helps restore ovulation frequency.
   
   

3. Support ovulation naturally: Nutrition, stress reduction, and medical therapies (like letrozole or clomiphene) can help induce ovulation.
   
   

4. Consider progesterone therapy: For some women, bioidentical progesterone may be used to regulate cycles and protect the uterine lining.
   
   

5. Work with a hormone-focused provider: Proper labs and personalized care ensure you’re not left guessing.
   
   

Takeaways

• Progesterone is only made after ovulation, and most women with PCOS ovulate irregularly.
  
  

• Progesterone deficiency contributes to irregular cycles, infertility, anxiety, poor sleep, and endometrial risks.
  
  

• Without progesterone, estrogen imbalances (low E2, high E1) get worse.
  
  

• Supporting ovulation and reducing insulin resistance are the best ways to restore progesterone naturally.
  
  

• Precision care—including ovulation tracking and targeted therapies—is essential for managing PCOS.
  
  

Final Word

Progesterone is the missing piece in the PCOS hormone puzzle. Without it, cycles become irregular, uterine health is compromised, and hormonal imbalances spiral further out of control. By recognizing that progesterone deficiency comes from under-ovulation, women with PCOS can take targeted steps toward restoring balance, improving fertility, and protecting long-term health.

References

• Azziz, R., Carmina, E., Chen, Z., Dunaif, A., Laven, J. S., Legro, R. S., ... & Yildiz, B. O. (2016). Polycystic ovary syndrome. Nature Reviews Disease Primers, 2(1), 1-18. https://doi.org/10.1038/nrdp.2016.57
  
  

• Legro, R. S. (2013). Obesity and PCOS: implications for diagnosis and treatment. Seminars in Reproductive Medicine, 31(6), 496–506. https://doi.org/10.1055/s-0033-1356480
  
  

• Rosenfield, R. L., & Ehrmann, D. A. (2016). The pathogenesis of polycystic ovary syndrome (PCOS): the hypothesis of PCOS as functional ovarian hyperandrogenism revisited. Endocrine Reviews, 37(5), 467–520. https://doi.org/10.1210/er.2015-1104
  
  

• Palomba, S., Santagni, S., Falbo, A., & La Sala, G. B. (2015). Complications and challenges associated with polycystic ovary syndrome: current perspectives. International Journal of Women’s Health, 7, 745–763. https://doi.org/10.2147/IJWH.S70314