An embryo biopsy is a procedure performed during assisted reproductive technologies, most notably in vitro fertilization (IVF). It involves the removal of a small number of cells from an early-stage embryo. This sample is then prepared for genetic analysis. The technique allows for examination of the embryo’s genetic makeup before it is transferred into the uterus.
Understanding Embryo Biopsy
Embryo biopsy is primarily performed to facilitate Preimplantation Genetic Testing (PGT), which screens embryos for genetic conditions before implantation. One common application is Preimplantation Genetic Testing for Aneuploidy (PGT-A), which assesses embryos for chromosomal abnormalities. Aneuploidy refers to an incorrect number of chromosomes, such as an extra or missing chromosome (e.g., Trisomy 21, Down syndrome). This testing identifies embryos with the correct number of chromosomes, potentially improving implantation rates and reducing miscarriage risk.
Another use is Preimplantation Genetic Testing for Monogenic/Single Gene Diseases (PGT-M). This testing is for couples who are carriers of, or affected by, a single gene disorder. Examples include cystic fibrosis, Tay-Sachs disease, or Huntington’s disease, caused by a specific gene mutation. PGT-M identifies embryos with the specific genetic mutation, allowing selection of unaffected embryos for transfer.
Preimplantation Genetic Testing for Structural Rearrangements (PGT-SR) is also performed using biopsy samples. This testing is for individuals who carry a chromosomal structural rearrangement (e.g., translocation or inversion) but are otherwise healthy. These rearrangements can lead to an imbalance of genetic material, resulting in recurrent miscarriages or birth defects. PGT-SR identifies embryos with a balanced set of chromosomes, reducing adverse outcomes.
The Biopsy Process
Embryo biopsy is performed when the embryo reaches the blastocyst stage, on day five or six after fertilization. At this stage, the embryo has 100-200 cells and has differentiated into two main parts: the inner cell mass (which will form the fetus) and the trophectoderm (which will develop into the placenta and other extra-embryonic tissues).
During the biopsy, an embryologist uses a laser or a fine needle to create an opening in the embryo’s outer shell, known as the zona pellucida. Through this opening, five to ten trophectoderm cells are aspirated or pulled away from the embryo. These cells are separated from the embryo structure.
After the biopsy, the embryo is vitrified, a rapid freezing process, and stored in liquid nitrogen. The biopsied cells are sent to a laboratory for genetic analysis, which can take several days to weeks. The embryo remains frozen until genetic test results are available, allowing for the selection of chromosomally normal embryos or those free of specific genetic mutations for a subsequent frozen embryo transfer.
Factors Influencing the Decision
The decision to perform an embryo biopsy for genetic testing is influenced by several patient-specific factors and medical considerations. It is recommended for women over 35 due to an increased risk of aneuploidy in their embryos. Couples with recurrent pregnancy loss or multiple failed IVF cycles may also be advised to consider PGT-A to identify chromosomally normal embryos that are more likely to implant successfully.
For individuals with a family history of a specific genetic condition or carriers of a monogenic disorder, PGT-M is a consideration. This testing can prevent genetic disease transmission to offspring. Couples with a partner carrying a chromosomal structural rearrangement may opt for PGT-SR to increase their chances of a successful, healthy pregnancy.
Embryo biopsy and PGT can improve IVF success rates by identifying embryos with higher implantation potential. This also reduces miscarriage risk from chromosomal abnormalities and helps families avoid severe genetic disorders. However, considerations include the additional cost of PGT, minimal risk of embryo damage during biopsy, and the emotional impact of waiting for results or receiving abnormal findings.
For young, fertile couples without a history of genetic conditions or recurrent pregnancy issues, embryo biopsy may not be considered necessary. If PGT is not performed, prenatal diagnostic options like chorionic villus sampling (CVS) or amniocentesis are available later in pregnancy to assess fetal genetic health. Ultimately, the decision involves discussion between the patient and their reproductive endocrinologist, weighing benefits against risks and personal circumstances.