Case report: Eggs with rare perivitelline space defect lead to healthy twins

Researchers in 2023 report on a case where a patient had eggs with an abnormal perivitelline space (PVS), which led to the development of the embryo outside of the zona. Transfer of this embryo, and another, led to twins.

The PVS is the open space between the egg and the zona, as shown below:

For more background on egg quality and morphology, check out my Complete guide to egg quality.

In this case report, a 30 year old women had her first IVF cycle and retrieved 15 eggs, 13 of which had a high level of inclusions in the PVS:

These weren’t fragments, which is sometimes seen in eggs as an abnormal morphological feature, but were instead believed to be cumulus cells. Cumulus cells are cells that surround the egg that nurture it as it develops in the follicle.

The only other instance the authors have seen this is in a mouse study where the ZP1 gene was knocked out, resulting in a zona that was thinner than normal. Because of the weakened zona, cumulus cells were able to infiltrate the PVS.

A similar process may have occurred here in this case study.

Because of all the cumulus cells in the PVS, the polar body was obscured. The polar body is a structure that indicates whether or not an egg is mature, which is also located in the PVS and shown in the image above. Additionally, the location of the polar body is important because it allows the embryologist to position the egg during ICSI to avoid damaging it. If the embryologist can’t see the polar body, they’re essentially performing ICSI blind.

Of the 15 eggs, 2 were fertilized normally. One developed into a 5CC and the other into a 5BB. You can see a video of the 5BB below. As the embryo develops, the zona breaks down and the embryo’s cells start to grow outside of the zona.

Both the 5BB and 5CC were transferred and after an uneventful pregnancy, twins were born at 40 weeks with normal weight and karyotype.

Reference

Ferri D, Baldini D, Maria Baldini G. A successful twin healthy live birth achieved from eggs with a rare perivitelline space abnormality: A case report. Int J Reprod Biomed. 2023 Apr 14;21(3):263-267. doi: 10.18502/ijrm.v21i3.13202. PMID: 37122891; PMCID: PMC10133736.

 

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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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