Figure 3.

Biopsy methods for preimplantation genetic analysis. There are several stages at which material can be collected for preimplantation genetic analysis. Collection at the earliest stage involves removal of a polar body after the completion of meiosis I or meiosis II. Depicted is collection after fertilization (two pronuclei) and extrusion of the second polar body. Blastomere biopsy at the cleavage stage is typically performed when the embryo contains six to eight blastomeres; one to two blastomeres are retrieved from a single embryo. Trophectoderm biopsy is most frequently performed just before spontaneous embryo hatching from the zona pellucida on day 5 postfertilization (pf) and retrieves several trophectoderm cells. All biopsy methods involve manipulation of the zona pellucida. Using mechanical, chemical or laser-assisted techniques, a breach in the zona pellucida is made at the time of collection in polar body and cleavage stage blastomere biopsies. With trophectoderm biopsy, the zona pellucida is thinned on approximately day 3 pf, creating an area for preferential herniation of the trophectoderm on day 5 pf, just before spontaneous hatching. Trophectoderm cells are typically retrieved using laser-assisted techniques.