Understanding mosaic embryos and where they fit into the IVF process

When patients start IVF, they may feel that their lives are consumed by blood tests, ultrasound exams, fertility medications and office visits. For those who choose preimplantation genetic testing (PGT) for their embryos, one additional challenge may arise if mosaic embryos are identified. These embryos have a mix of normal and abnormal chromosomes. Our Nashville fertility clinic team is here to help patients understand their options in these cases.

What are mosaic embryos?

After fertilization, embryo development begins. Generally, each embryo has 46 chromosomes: 23 from the biological mother and 23 from the biological father. These chromosomes will help determine your baby’s sex and physical traits. Sometimes, normal development goes awry, resulting in embryo abnormalities.

When the IVF process includes PGT, our Nashville fertility clinic doctors will see the following types of embryos.

• Euploid embryos are genetically normal and contain 46 chromosomes.
• Aneuploid embryos have either too many or too few chromosomes.
• Mosaic embryos have a mix of normal and abnormal chromosomes.

What role does preimplantation genetic testing play?

Many IVF patients choose PGT to improve the chances of success. At our Nashville fertility clinic, we commonly employ preimplantation genetic testing for aneuploidy (PGT-A), which involves genetic testing of a small number of cells taken from each embryo via biopsy. This test enables our embryologists to choose only chromosomally normal embryos for transfer to the uterus.

PGT-A can confirm if an embryo is normal (euploid) or abnormal (aneuploid). However, embryos can also be classified as mosaic, which means they have cells containing normal chromosomes as well as cells with abnormal chromosomes. Roughly 20 percent of embryos are labeled as mosaic. Within mosaic embryos, degrees of irregularity exist, which means some embryos have lower levels of abnormality than others.

Should you transfer these embryos?

A decision about whether to transfer these embryos is complex and personal. We always arrange for patients to meet with a genetic counselor to discuss their test results and options. However, if euploid embryos are available, our doctors recommend using those embryos first. While mosaic embryos could result in a healthy pregnancy, using these embryos can increase the risk of failed implantation, miscarriage and/or birth defects.

When you are going through IVF, the road to parenthood can feel challenging. A mosaic test result may add another layer of complexity to your journey. We are here to guide you through, providing the information you need to make informed decisions at every step. Contact our office for more information or to schedule an appointment with one of our Nashville fertility clinic doctors.