Aspects of biopsy procedures prior to preimplantation genetic diagnosis

Abstract

Today, preimplantation genetic diagnosis (PGD) is offered in over 40 centres worldwide for an expanded range of genetic defects causing disease. This very early form of prenatal diagnosis involves the detection of affected embryos by fluorescent in situ hybridization (FISH) (sex determination or chromosomal defects) or by polymerase chain reaction (PCR) (monogenic diseases) prior to implantation. Genetic analysis of the embryos involves the removal of some cellular mass from the embryos (one or two blastomeres at cleavage-stage or some extra-embryonic trophectoderm cells at the blastocyst stage) by means of an embryo biopsy procedure. Genetic analysis can also be performed preconceptionally by removal of the first polar body. However, additional information is then often gained by removal of the second polar body and/or a blastomere from the embryo. Removal of polar bodies or cellular material from embryos requires an opening in the zona pellucida, which can be created in a mechanical way (partial zona dissection) or chemical way (acidic Tyrode's solution). However, the more recent introduction of laser technology has facilitated this step enormously. Different biopsy procedures at different preimplantation stages are reviewed here, including their pros and cons and their clinical applications. The following aspects will also be discussed: safety of zona drilling by laser, use of Ca2+/Mg2+-free medium for decompaction, and removal of one or two cells from cleavage-stage embryos.

Arrested human embryos are more likely to have abnormal chromosomes than developing embryos from women of advanced maternal age

“…Currently, PGS is performed in samples biopsied from polar bodies [10-13], cleavage embryos [14,15] or blastocysts [16,17]. It has been found that blastocysts have less mosaicism than cleavage embryos, thus most laboratories prefer blastocyst biopsy, in which multiple cells from the trophectoderm (TE) are biopsied and used for screening [8,9].…”

Delivery of a chromosomally normal child from an oocyte with reciprocal aneuploid polar bodies

“…In contrast, the European Society of Human Reproduction and Embryology (ESHRE) Preimplantation Genetic Screening (PGS) Task Force has initiated a multicenter RCT to characterize the utility of polar body aCGH [9]. Each approach has a variety of theoretical limitations that are both technical and biological in nature [10]. …”

The effect of blastomere biopsy on preimplantation mouse embryo development and global gene expression

“…PGT requires a highly invasive biopsy procedure that involves 1) incubating embryos in divalent-cation-deficient medium to disrupt cell adhesion, 2) breaching the protective zona pellucida with acid Tyrode’s solution, laser drilling, or mechanical force and 3) aspirating one or two blastomeres (5). A widely cited study using human embryos demonstrated that blastomere biopsy at the 8-cell stage do not appear to affect preimplantation development, and although embryo metabolism and cell number are reduced, both parameters are proportional to the embryo’s reduced cellular mass (6).…”