As a woman goes through ovulation each month, a cohort of follicles will begin developing in the ovaries. Typically, only one dominant follicle will reach full maturity and release an egg, while the rest of the follicles in that cohort will stop developing and die off. This is a normal physiological process, but it often leaves women wondering why multiple follicles don’t mature and ovulate during each cycle.
The follicle recruitment process
Follicle development begins well before ovulation occurs. In the early stages of the menstrual cycle, a hormone called follicle-stimulating hormone (FSH) stimulates the recruitment of a cohort of follicles to begin maturing. This cohort goes through several stages of development:
- Primordial follicle – immature follicle
- Primary follicle – starts growing but still immature
- Secondary follicle – more developed but still not mature
- Tertiary (antral) follicle – fluid-filled space forms inside
- Dominant follicle – one follicle outgrows the others due to greater sensitivity to FSH
Typically, only the dominant follicle will make it to the final stages of development and ovulate. The remaining follicles in the cohort will stop growing and undergo atresia (cell death).
Why doesn’t every follicle ovulate?
There are several reasons why most ovarian follicles do not reach full maturity each cycle:
- Hormone levels – As the dominant follicle grows, it produces increasing amounts of estrogen. High estrogen levels trigger a negative feedback response that suppresses FSH release from the pituitary gland. With less FSH stimulation, the smaller follicles cannot continue growing and ovulating.
- Apoptosis – Specialized granulosa cells in the follicles undergo programmed cell death (apoptosis) in response to hormonal signals. This leads to atresia of all follicles except the dominant one.
- Limited resources – The ovary has a finite capacity to support multiple fully grown follicles. Dominant follicles take up the majority of available blood supply and nutrients.
- Preventing multiples – If more than one follicle ovulated, it could result in dizzyygotic (fraternal) twins or triplets. Generally, the body aims to avoid this higher-risk scenario.
How many follicles mature each cycle?
Research shows that on average, a cohort of 10-20 follicles will start developing each menstrual cycle. However, only one dominant follicle usually reaches full maturity and ovulates.
In some cases, two or more follicles may ovulate. This occurs more often in:
- Younger women
- Women with a family history of dizygotic twins
- Women taking fertility medications
Having two follicles ovulate can result in fraternal twins, while three follicles ovulating could lead to triplets. More than that would be extremely rare in natural conception.
Factors affecting follicle growth
A number of factors can influence how many follicles fully develop each cycle:
- Age – Younger women recruit more follicles per cycle. As women get older, both quantity and quality of follicles decline.
- Ovarian reserve – Women are born with a finite number of follicles. Declining ovarian reserve due to age or other causes reduces follicle numbers.
- Genetics – Some women inherit a predisposition for hyper-ovulation and releasing multiple eggs.
- Medications – Fertility drugs like Clomid purposefully stimulate extra follicles for ovulation.
- Ovarian issues – Problems like PCOS may increase follicle growth and ovulation.
- Lifestyle factors – Diet, exercise, smoking, alcohol use, and stress can impact ovarian function.
Tracking follicle growth
To monitor the development of ovarian follicles throughout your cycle, doctors can perform ultrasound monitoring. This allows them to visualize and measure follicle sizes over time.
Typical follicle sizes during a cycle:
| Follicle Stage | Size |
|---|---|
| Preantral follicle | Less than 10mm |
| Antral/Tertiary follicle | 10-22mm |
| Preovulatory follicle | Greater than 22mm |
Doctors look for the dominant follicle to reach around 20mm or more before ovulation. Seeing multiple large follicles could suggest a risk of multiples.
Improving follicle development
If you are trying to conceive and not ovulating, there are steps you can take to support better follicle growth:
- Take a fertility supplement containing myo-inositol to improve insulin sensitivity and egg quality.
- Reduce stress through yoga, meditation, or other relaxation techniques.
- Maintain a healthy BMI through diet and exercise.
- Quit smoking and avoid secondhand smoke.
- Limit alcohol intake.
- Seek treatment for any suspected reproductive issues like PCOS or endometriosis.
Your doctor may also prescribe medications like clomiphene citrate, gonadotropins, or metformin to promote ovulation in follicles.
When to see a doctor
See your doctor if you experience any of the following, which could indicate an ovulation disorder or underlying health condition:
- No dominant follicle becomes apparent on ultrasound monitoring
- Multiple mature follicles develop each cycle
- Irregular, absent, or infrequent periods
- Hormonal imbalances on blood tests
- Known or suspected PCOS, endometriosis, or other ovarian issues
Your doctor can help determine if you have a condition preventing normal follicle development and recommend appropriate treatment options.
Conclusion
Typically, only one dominant ovarian follicle fully matures and releases an egg each cycle. The remaining follicles become atretic and die off due to hormonal influences, limited resources, and mechanisms that prevent multiple births. Factors like age, genetics, medications, ovarian issues, and lifestyle can impact the follicle recruitment process. If you’re concerned about lack of follicular development or hyper-ovulation, see a doctor for proper diagnosis and care.