Should You Transfer a Mosaic Embryo?

Approximately 20 percent of embryos created for in vitro fertilization (IVF) are mosaic embryos. But what exactly is a mosaic embryo and what are the risks?

What is a mosaic embryo?

For families undergoing IVF treatments, reproductive specialists have typically considered mosaic embryos unusable. Physicians use Preimplantation Genetic Screening (PGS), also known as Preimplantation Genetic Testing (PGT), to determine whether an embryo has normal, abnormal or a mixture of normal and abnormal cells in a developing embryo.

Following IVF, reproductive specialists analyze each embryo and classify them into three categories: normal (euploid), abnormal (aneuploid) and mosaic. Embryos classified as normal contain only normal cells and are approved to transfer back into a woman’s uterus; abnormal embryos are not approved. Mosaic embryos fall somewhere in the middle because they contain both normal and abnormal cells.

Most fertility clinics do not recommend transferring mosaic embryos due to their heightened risk of miscarriage or birth disorders like Mosaic Down syndrome and Pallister-Killian mosaic syndrome, however, new research shows up to 40 percent of mosaic embryos can result in a healthy baby.

Should I transfer a mosaic embryo?

Despite the risks, some highly skilled IVF doctors are beginning to consider the use of mosaic embryos—especially in instances where they are the last option for achieving pregnancy. The transfer of mosaic embryos is not taken lightly; here are the current recommendations regarding the use of mosaic embryos to attempt pregnancy:

1. The embryology lab should report the percentage of abnormal cells in any mosaic embryo.
2. The embryology lab should provide sensitivity information about their testing platform. For example, can they detect mosaic embryos that have less than 20 percent abnormal cells?
3. Mosaic embryos should only be used if there are no normal embryos available (or another IVF cycle is not possible).
4. Women considering a mosaic embryo transfer should be completely informed about the risks of miscarriage, birth disorders and be required to have a consultation with a genetic counselor who is knowledgeable about mosaic syndromes.
5. Mosaic embryos with more than one type of abnormal cells and/or 40 percent or more abnormal cells should only be used if there are no other, better quality, options.

A highly qualified physician should only perform PGS and Preimplantation Genetic Diagnosis (PGD) techniques. Dr. Lori Arnold is a board-certified fertility specialist at California Center for Reproductive Medicine (CACRM) in San Diego, CA. With her knowledge and expertise, she can provide insights on the chances of a successful pregnancy and the possibilities of genetic disorders with a mosaic embryo.

For more information about transferring a mosaic embryo in San Diego, please call 760-274-2000. We are here to help you along your journey toward parenthood.