Pre-implantation genetic screening and diagnosis: what doctors should know - Revista Brasileira de Ginecologia e Obstetrícia

Pre-implantation genetic screening and diagnosis: what doctors should know |

Introduction

Trends toward delayed childbearing have resulted in an increasing number of women of advanced maternal age (AMA) seeking to become pregnant and in a consequent increase in demand for assisted reproductive technology, most commonly in-vitro fertilization (IVF). In such women, the proportion of aneuploid embryos can exceed 60%, with a risk of miscarriage of about 40%, potentially resulting in significant emotional and financial hardship for affected couples. In the last 30 years, genetic testing techniques have been developed to identify chromosomally normal embryos in vitro, thereby potentially increasing the proportion of successful cycles with elective single-embryo transfer, and minimizing twin-pregnancy complications and miscarriages. This testing is termed "pre-implantation genetic screening" (PGS), in contrast to pre-implantation genetic diagnosis, in which testing is performed for specific genetic defects. Collectively, these techniques are called pre-implantation genetic testing. Today, PGS technologies have evolved to include screening of all 24 chromosomes (22 pairs of autosomes and the 2sex chromosomes). Ongoing pregnancy rates of about 60% following single embryo transfer have been described in couples with a maternal age of 38 years whose embryos have undergone PGS. It has not, however, been definitively established that the cumulative delivery rates are better with PGS, although it has been argued that the reduction in miscarriage rates and maternal and neonatal complications due to multiple pregnancies justifies the expense of this technology. [...]