What is Controlled Ovarian Hyperstimulation? How COH Supports IVF and Egg Freezing
Quick answer: Controlled ovarian hyperstimulation (COH) is the use of injectable fertility medications to stimulate the ovaries to mature multiple eggs in a single cycle. This approach makes IVF and egg freezing possible by increasing the number of eggs available for fertilization, embryo creation, and future use.
Controlled ovarian hyperstimulation (COH) is one of the most important reasons in vitro fertilization (IVF) and egg freezing are effective fertility treatments. By stimulating the ovaries to mature multiple follicles in a single cycle, COH makes it possible to retrieve several eggs at once, which does not occur naturally.
This ability to retrieve multiple eggs is central to IVF and egg freezing success. Not every egg will fertilize, and not every fertilized egg will develop into a healthy embryo. Controlled ovarian hyperstimulation creates the opportunity to generate enough eggs and embryos to support fertilization, embryo selection, freezing, and future transfer attempts.
While COH is more intensive than mild ovarian stimulation, it is carefully designed, closely monitored, and personalized to balance effectiveness and safety.
Fast Facts About Controlled Ovarian Hyperstimulation
- COH is used in IVF, egg freezing, and embryo banking
- The goal is to mature multiple follicles in one cycle
- Medications are injectable and act directly on the ovaries
- Monitoring includes ultrasound and bloodwork
- Protocols are individualized and adjusted in real time
What Is Controlled Ovarian Hyperstimulation?
Controlled ovarian hyperstimulation refers to the use of injectable fertility medications to stimulate the ovaries to develop multiple follicles simultaneously. Each follicle contains an egg, which may be retrieved once the follicles have matured.
In a natural menstrual cycle, the body typically selects one dominant follicle to ovulate. COH overrides this natural selection process so that many follicles continue developing at the same time, increasing the number of eggs available for retrieval.
This process is a defining feature of IVF and egg freezing and underlies many of the advantages these treatments offer over natural conception.
Why Controlled Ovarian Hyperstimulation Is Used
Controlled ovarian hyperstimulation is used because IVF and egg freezing depend on having access to more than a single egg.
In a natural cycle, the body typically matures and ovulates one egg. While IVF can technically be performed with one egg, success rates are significantly lower because:
- Not every egg fertilizes
- Not every fertilized egg develops into a viable embryo
- Not every embryo results in pregnancy
By stimulating the ovaries to develop multiple follicles, COH increases the number of eggs available for retrieval. This is one of the fundamental mechanisms that allows IVF and egg freezing to achieve meaningful success rates.
Controlled ovarian hyperstimulation supports treatment success by:
- Increasing the number of eggs retrieved in a single cycle
- Improving the chance of creating viable embryos
- Allowing embryos to be evaluated and selected for transfer
- Enabling embryo freezing for future attempts
- Supporting genetic testing when indicated
- Reducing the need for repeated egg retrievals
Without controlled ovarian hyperstimulation, many of the advantages that distinguish IVF and egg freezing from natural conception would not be possible.
When Controlled Ovarian Hyperstimulation Is Recommended
COH is typically used for:
- In vitro fertilization (IVF)
- Egg freezing (oocyte cryopreservation)
- Embryo banking
- IVF with preimplantation genetic testing
It is not commonly used for timed intercourse or IUI cycles, which generally rely on ovulation induction or mild ovarian stimulation.
How Controlled Ovarian Hyperstimulation Works
Controlled ovarian hyperstimulation usually begins early in the menstrual cycle and lasts approximately 8 to 14 days, though timing varies based on individual response.
During this phase:
- Injectable medications stimulate follicle growth in the ovaries
- Ultrasound and bloodwork monitor follicle development and hormone levels
- Medication doses may be adjusted based on response
- Ovulation is actively prevented until eggs are ready
Once follicles reach an appropriate size, a trigger medication is given to induce final egg maturation and precisely time egg retrieval.
Medications Used in Controlled Ovarian Hyperstimulation
COH protocols involve several categories of medications, each serving a specific role in the stimulation process.
Follicle-Stimulating Medications
These injectable medications provide follicle-stimulating hormone (FSH), sometimes combined with luteinizing hormone (LH) activity, to stimulate the ovaries directly. Common examples include Follistim, Gonal-F, Menopur, and Micro-dose hCG.
Ovulation Suppression Medications
Medications such as GnRH antagonists are used during COH to prevent premature ovulation while follicles are developing.
Trigger Medications
Trigger medications are used to induce final egg maturation and allow egg retrieval to be timed precisely. Depending on the protocol and individual risk factors, this may include hCG, a GnRH agonist, or a dual-trigger approach.
Monitoring During Controlled Ovarian Hyperstimulation
Because COH produces a strong ovarian response, careful monitoring is essential.
Monitoring typically includes:
- Transvaginal ultrasounds to measure follicle growth
- Blood tests to track hormone levels such as estradiol
Monitoring allows care teams to:
- Adjust medication doses
- Optimize egg maturity
- Reduce the risk of complications
- Determine the ideal timing for egg retrieval
Personalizing COH Protocols
No two patients respond to controlled ovarian hyperstimulation in the same way. Protocols are individualized based on factors such as:
- Age
- Ovarian reserve markers such as AMH and antral follicle count
- Prior response to ovarian stimulation
- Underlying diagnoses such as PCOS or diminished ovarian reserve
- Risk for ovarian hyperstimulation syndrome (OHSS)
Medication types and doses may be adjusted throughout the cycle based on real-time ovarian response rather than following a rigid protocol.
Controlled Ovarian Hyperstimulation and OHSS
Ovarian hyperstimulation syndrome (OHSS) is a potential complication of COH and occurs when the ovaries respond too strongly to stimulation.
Modern IVF protocols have significantly reduced the risk of severe OHSS through:
- Individualized dosing
- Careful monitoring
- Use of GnRH agonist trigger strategies when appropriate
- Freeze-all approaches in higher-risk patients
Most patients experience mild or no symptoms, and severe cases are uncommon with modern care.
What Controlled Ovarian Hyperstimulation Feels Like
As follicles grow and ovaries enlarge, some patients experience:
- Bloating or abdominal fullness
- Pelvic pressure
- Mild abdominal discomfort
- Fatigue
- Injection-site soreness
These effects are typically temporary and improve after egg retrieval.
Emotional and Practical Considerations
Controlled ovarian hyperstimulation involves daily injections, frequent appointments, and uncertainty around response and outcomes. Emotional ups and downs during this phase are common and do not predict treatment success or failure.
Monitoring appointments are often scheduled early in the morning to minimize disruption to work and daily routines.
Controlled Ovarian Hyperstimulation FAQs
Does IVF always require controlled ovarian hyperstimulation?
Nearly always. Outside of the very rare, natural IVF protocol, IVF requires ovarian stimulation to retrieve multiple eggs in a single cycle.
When does COH start during IVF?
COH typically begins early in the menstrual cycle, often within the first few days of a period.
Are COH medications always injectable?
Yes. Controlled ovarian hyperstimulation requires injectable medications to directly stimulate the ovaries.
How many eggs are retrieved during COH?
The number varies widely depending on age and ovarian reserve. There is no single ideal number for all patients.
Can COH be done back-to-back?
In some cases, back-to-back cycles may be possible, depending on recovery and individual response.
Can I exercise during COH?
Light activity is usually encouraged, but high-impact or twisting exercises are often restricted to reduce the risk of ovarian torsion.
Controlled Ovarian Hyperstimulation: The Takeaway
Controlled ovarian hyperstimulation is a foundational component of IVF and egg freezing. By enabling the development and retrieval of multiple eggs in a single cycle, COH makes fertilization, embryo selection, freezing, and future transfer attempts possible.
When thoughtfully designed and carefully monitored, controlled ovarian hyperstimulation maximizes treatment potential while prioritizing safety and individualized care.
