Achilleas Papatheodorou, PhD., M.Med.Sc., Senior Clinical Embryologist, ESHRE certified, Lab Director
In the fascinating world of assisted reproduction, few topics have attracted as much attention as mosaic embryos. These are embryos that contain both normal (euploid) and abnormal (aneuploid) cells in their chromosomal composition. For many years, such findings automatically excluded these embryos from transfer, as even the presence of a small number of abnormal cells was considered to mark the embryo as non-viable. However, advances in genetic analysis and a deeper understanding of embryonic development have reshaped this perception.
With the progress of Next Generation Sequencing (NGS) technology, we can now detect mosaicism with far greater sensitivity. This progress has created new possibilities—but also new challenges. While we know more than ever before, interpreting these findings remains complex.
What does mosaicism mean in practice?
Practically speaking, mosaicism is not an ideal condition for an embryo. For some reason, an embryo that initially had only normal cells may develop some abnormal ones at around day 3 or 4 after fertilization. This appears to represent a biological challenge—one that, according to recent studies, the embryo often tries to manage by eliminating or isolating the abnormal cells. Sometimes it succeeds; other times it does not.
In light of these recent scientific insights, the clinical interpretation of mosaic embryos has evolved, and such embryos are now considered potentially usable in IVF treatments.
However, not all mosaic embryos are the same. The extent and type of chromosomal abnormality play a decisive role. For instance, embryos with low-level mosaicism (a small proportion of abnormal cells) have shown implantation potential and developmental outcomes comparable to euploid embryos. In contrast, embryos with high-level mosaicism or involving certain chromosomes may have lower chances of success.
Nevertheless, embryos often possess self-correction mechanisms, which can lead to normal pregnancies and the birth of healthy children.
Clinical evidence and decision-making
In recent years, an increasing number of studies have shown that transferring mosaic embryos—especially when no euploid embryos are available—can still offer realistic chances of pregnancy and live birth. Large multicentre studies and international registries have demonstrated that, although implantation rates are somewhat lower, the rates of healthy newborns remain highly encouraging.
Major scientific societies, such as ESHRE and ASRM, now recognize the role of mosaic embryos in clinical practice under specific conditions. They emphasize the need for accurate genetic counselling, careful prioritization based on the level of mosaicism, and transparent communication with the couple.
The human and ethical dimension
For many couples, mosaic embryos represent a bridge between uncertainty and hope. The decision to transfer them is not only a scientific matter—it is also a deeply personal and emotional one. Each case is unique and requires individualized consideration.
At Embryolab
Our team combines state-of-the-art scientific knowledge with responsible, compassionate guidance. We work closely with specialized genetic laboratories to ensure precise interpretation of results and provide detailed counselling so that every decision is informed and confident.
Thus, transferring a mosaic embryo is not a “last resort” but a carefully guided option—a point where science meets hope.
Mosaic embryos remind us that human life is far more dynamic and adaptable than we once imagined—and that even within imperfection, there may lie the beginning of something extraordinary.
