As a Florida surrogacy attorney, I am not going to get into the medical jargon of what a mosaic embryo is, however, as a simplified explanation, a mosaic embryo is one that is genetically tested and the testing shows an abnormal result for the embryo, referred to as "aneuploid", however such abnormality does not necessarily prevent the use of this embryo for a transfer. Preimplantation genetic testing of embryos is an evolving technology which testing procedure used to just indicate if an embryo was chromosomally normal or abnormal. The use of a mosaic embryo is essentially the in-between results of a tested embryo between the normal and abnormal range. As a lawyer, who handles matters that are not always straight forward, I refer to this as the "gray area" or the in-between space of embryos. To fully understand the medical concept of mosaic embryos and the safety of the use of such embryos, you need to speak to a reproductive doctor to obtain this information. With people waiting to have children later in life, and for a variety of other reasons, more and more tested embryos are coming back as mosaic embryos. They may not be fully genetically normal, however, with the recommendation of the reproductive doctor, they may still be safe and effective for use in an embryo transfer. The American Society for Reproductive Medicine ("ASRM"), has established medical guidelines and best practices relating to the use of mosaic embryos: https://www.asrm.org/globalassets/asrm/asrm-content/news-and-publications/practice-guidelines/for-non-members/clinical_management_of_mosaic_results_from_pgt-a.pdf Per the guidelines established by the ASRM, it is critical to consult with your reproductive doctor about the safety and effectiveness in using a mosaic embryo. The guidelines establish numerous points of genetic counseling to the patients which includes genetic counseling prior to the use of the embryos (pretest counseling), and possibly genetic counseling after the embryos are transferred (posttest counseling). Fertility clinics are encouraged to create a policy for the transfer and storage of mosaic embryos which policy should be shared with the patient prior to the start of a cycle and at points throughout the process. In the context of surrogacy, it appears per the ASRM guidelines that the use of a mosaic embryo may later require invasive testing that may not be recommended with a genetically normal embryo. What come to mind from a legal perspective with the use of a mosaic embryo in the surrogacy context is whether the use of them requires greater use of invasive testing like placental testing (CVS) or fetal testing (amniocentesis (referred to sometimes as "amnio")) during a pregnancy. If so, surrogates should be informed of the risk that a form of invasive testing like CVS or amnio may be indicated during the pregnancy. It would be helpful to discuss with the surrogate prior to entering into a surrogacy agreement that she is OK to undergo these invasive tests and then to include that language in the surrogacy agreement. It could create a legal issue if the surrogate is not aware an invasive test will be needed and then later, is asked to undergo an invasive test and breaches her agreement with the intended parents because she doesn't want to perform a certain procedure. The more communication on any potential invasive procedure is just overall better to avoid any issues or concerns down the road once pregnancy is achieved.