Higher quality eggs with rescue IVM and cumulus cells

In a new study, researchers show that keeping cumulus cells attached during rescue IVM led to improved fertilization and embryo quality. This technique may help increase the number of viable embryos after IVF.

In a standard IVF cycle, mature and immature eggs can be collected. Rescue IVM is a way to “rescue” these immature eggs and make them mature, so they can be inseminated and develop into embryos. The immature eggs are cultured either for a few hours after retrieval or overnight, which causes them to mature.

Some studies have shown that eggs matured by rescue IVM are lower quality, and are less likely to fertilize and produce good quality embryos.

One way to potentially overcome this is by keeping the cumulus cells attached to the egg during rescue IVM. When eggs are collected during IVF, they are surrounded by special cells called cumulus cells. These cells produce growth factors that can help the egg mature and grow. After an egg retrieval, these cells are often removed (or “denuded“) in order to perform ICSI — check out the difference below!

eggs with or without cumulus cells after stripping or denudation — Modified from Ramirez et al. (2020), CC BY 4.0 and Ghevaria et al. (2022), CC by 4.0.

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In a new study, Sudewo et al. 2025 evaluated whether keeping cumulus cells attached to immature eggs during rescue IVM would improve outcomes. This was a retrospective study that took place at a fertility clinic in Indonesia, and included women aged 21 to 36 with unexplained infertility.

During the egg retrieval, they collected immature eggs that appeared normal (eggs with visible abnormalities were excluded from the study).

The maturity of each egg was assessed using a microscope to determine if the egg was immature (GV, M1) or mature (M2). Since cumulus cells can obscure the maturity of the egg, the cumulus mass was gently spread apart to allow visualization. In total, they identified 200 immature eggs across 413 egg retrieval cycles. These eggs were randomly divided into two groups of 100:

Without cumulus cells: This group underwent complete denudation of the egg (removal of cumulus cells).
With cumulus cells: This group retained their cumulus cells on the egg.

After this, both groups were cultured for an additional 24 hours in specialized IVM media, with 71% becoming mature in the group without cumulus cells and 73% in the group with cumulus cells (no statistical difference). These are the eggs that matured from rescue IVM.

ICSI was then performed on the rescue IVM matured eggs, with embryo development evaluated on days two and three after ICSI. Good-quality embryos were defined as having six to eight evenly sized cells with less than 20% fragmentation.

The group with cumulus cells had higher fertilization and cleavage rates, and ultimately produced a higher proportion of good-quality embryos compared to the group without cumulus cells. All these differences were statistically significant (p= 0.006, 0.005 and 0.003, respectively).

improved embryology outcomes for rescue IVM eggs with retained cumulus cells

Unfortunately, the researchers didn’t evaluate embryo transfer outcomes for the rescue IVM embryos, or evaluate blastocyst development. This is the first study to keep cumulus cells on during rescue IVM, so more work is needed to confirm the results! Still, it’s interesting to see that keeping cumulus cells on during rescue IVM can increase fertilization and the formation of good quality cleavage stage embryos!

Cumulus cells support immature eggs as they develop by providing nutrients and important cellular signals. For fertilization, an egg needs both nuclear and cytoplasmic maturation (read more about that here). Nuclear maturity involves the egg’s chromosomes and is visible by the presence of a polar body, but cytoplasmic maturity, which involves the buildup of essential molecules inside the egg’s fluid, is harder to detect but equally important. Keeping the cumulus cells on during rescue IVM may help support cytoplasmic maturity of the egg, allowing for increased fertilization and good quality embryo development.

Rescue IVM is a great way for patients to increase the number of mature eggs they have in a cycle — to learn more about rescue IVM, check out these posts:

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About Embryoman

Embryoman (Sean Lauber) is a former embryologist and the founder of Remembryo, an IVF research and fertility education website. After working in an IVF lab in the US, he returned to Canada and now focuses on making fertility research more accessible. He holds a Master’s in Immunology and launched Remembryo in 2018 to help patients and professionals make sense of IVF research. Sean shares weekly study updates on Facebook, Instagram, and Reddit regularly. He also answers questions on Reddit or in his private Facebook group.

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