Immature Eggs and Fertility Preservation: Where In Vitro Maturation Fits In

By Dr. Jessie Wai Leng Phoon, MRCOG
Medical Director, GenPrime Fertility Singapore
Last reviewed: January 2026

When fertility preservation is discussed, most people hear about freezing mature eggs after hormonal stimulation. But in some situations—such as urgent cancer treatment, medical contraindications to hormones, or time constraints—this standard approach isn’t always possible.

This is where in vitro maturation (IVM) enters the conversation.

IVM involves collecting immature eggs and maturing them in the laboratory before freezing or fertilisation. While promising in theory, it remains an evolving area of fertility preservation.

This article explains what IVM is, why it is being studied, and what clinical research—including a randomised study involving fertility specialists in Europe—tells us about its current potential and limitations. 

IVM for FP 2022

What are immature eggs?

Eggs retrieved from the ovary can be at different stages of development.

• Mature eggs (MII oocytes) are ready for fertilisation and are the gold standard for egg freezing.
• Immature eggs, often called germinal vesicle (GV) oocytes, have not yet completed maturation.

In a typical IVF or fertility preservation cycle:

• Around 10–20% of retrieved eggs are immature
• These eggs are often discarded in routine practice

Researchers have been exploring whether these immature eggs could be rescued and matured in the lab to increase the total number of usable eggs.

What is in vitro maturation (IVM)?

IVM is a laboratory process where immature eggs are:

1. Collected from the ovaries
2. Cultured in specialised media
3. Encouraged to mature outside the body

Potential advantages include:

• Less or no hormonal stimulation
• Faster timelines (important when cancer treatment cannot be delayed)
• Lower medication exposure

IVM is already used in selected situations, such as in women with polycystic ovary syndrome (PCOS) or those at high risk of ovarian hyperstimulation.

Why study IVM for fertility preservation?

In fertility preservation—especially for cancer patients—time and safety matter.

IVM has been proposed for women who:

• Cannot undergo hormonal stimulation
• Need to start chemotherapy urgently
• Are very young or prepubertal
• Have medical reasons to avoid high hormone exposure

Researchers are also interested in whether freezing eggs at different stages—before or after maturation—might improve outcomes.

What did this study look at?

This clinical study examined whether immature eggs could be:

• Matured in the lab (IVM)
• Frozen either before or after maturation
• Successfully fertilised and developed into embryos

The study compared:

• Fresh IVM eggs (no freezing)
• Eggs frozen after IVM
• Eggs frozen first, then matured after thawing

Researchers assessed:

• How many eggs matured successfully
• Fertilisation rates after ICSI
• Development to the blastocyst stage

What were the key findings?

Some immature eggs can mature—but not all

• Just over half of immature eggs matured successfully with IVM
• Maturation rates were slightly higher when eggs were matured before freezing, rather than after thawing

This suggests that timing matters, even at very early stages.

Freezing reduced fertilisation and embryo development

When eggs underwent freezing (either before or after IVM):

• Fertilisation rates were significantly lower
• Fewer embryos reached the blastocyst stage

Fresh IVM eggs (not frozen) performed better than those that were frozen at any stage.

Developmental potential remains limited

Although a small number of embryos developed normally:

• Overall efficiency was low
• The study reinforces that IVM eggs do not yet perform as well as mature eggs obtained through standard stimulation

This is an important point for patient counselling.

Why is IVM still considered experimental?

Egg maturation is not just about nuclear changes—it also involves complex cytoplasmic development, which is harder to replicate outside the body.

Challenges include:

• Loss of supportive cells during egg processing
• Sensitivity of immature eggs to freezing and thawing
• Potential effects on later embryo development

Because of these uncertainties, IVM—especially when combined with freezing—is not yet a first-line fertility preservation method.

When might IVM still be considered?

Despite its limitations, IVM may still have a role in selected situations, such as:

• Patients who cannot delay cancer treatment
• Women who cannot safely undergo ovarian stimulation
• Cases where every possible egg matters

In these scenarios, IVM may be offered with careful counselling, as a way to potentially increase fertility preservation options—not as a guaranteed solution.

How this affects real-world fertility counselling

For most patients:

• Freezing mature eggs remains the gold standard
• IVM is considered adjunctive or experimental

An experienced fertility team will explain:

• What is proven
• What is still evolving
• What expectations are realistic

Clear counselling helps patients make decisions without false reassurance.

Questions to ask your doctor

If IVM has been mentioned as an option, consider asking:

• Why is IVM being recommended in my case?
• Are mature egg freezing options possible for me?
• What are the success rates compared with standard egg freezing?
• Will frozen IVM eggs be usable for future IVF?
• Are there safety or long-term data I should know about?

A simple next step

If you’re exploring fertility preservation under time or medical constraints, ask for a detailed discussion about all available options—including their limits.

Understanding where IVM fits today can help you make informed decisions grounded in evidence, not assumptions.