Abstract
Chromosome abnormalities are extremely common in human oocytes and embryos and are
associated with a variety of negative outcomes for both natural cycles and those using
assisted conception techniques. Embryos containing the wrong number of chromosomes
(aneuploidy) may fail to implant in the uterus, miscarry, or lead to children with
serious medical problems (e.g., Down syndrome). Preimplantation genetic screening
(PGS) is a method that seeks to improve the outcomes of assisted reproductive treatments,
such as in vitro fertilization (IVF), by ensuring that the embryos chosen for transfer
to the uterus are chromosomally normal. Here we summarize published and novel data
concerning the frequency and variety of chromosomal abnormalities seen in oocytes
and embryos at the cleavage and blastocyst stages of development. Clinical outcomes
of studies using PGS are presented, and the controversy over the use of chromosome
screening as a tool for embryo selection is discussed. We describe validation and
preliminary clinical data from the new generation of methods being used for PGS, including
comparative genomic hybridization (CGH), microarrays (aCGH and single nucleotide polymorphism
arrays), and quantitative polymerase chain reaction. These methodologies allow comprehensive
chromosomal analysis, provide high accuracy, and have yielded encouraging preliminary
clinical data. The combination of advances in genetics and embryology seems poised
to usher in a new era in the treatment of infertility.
Keywords
preimplantation genetic screening - embryo - oocyte - FISH - aCGH
