Preimplantation genetic screening (PGS) is essentially an alternative to prenatal diagnosis, in which genetic testing is performed on embryos produced by in vitro fertilization (IVF) before a pregnancy is established. PGS is mostly commonly used by women of advanced maternal age who are undergoing IVF.
PGS is also used to screen for chromosomal abnormalities, in order to decrease the potential for miscarriage for the transfer of chromosomally abnormal embryos.
Preimplementation genetic diagnosis (PGD) allows for the detection of single gene disorders present in embryos grown in vitro. The number of single gene disorders (disease caused by genetic defects) that can now be diagnosed with PGD continues to grow. Diseases such as Cystic Fibrosis, Fragile X Syndrome, Myotonic Dystrophy, Thalassemia, and Tay Sachs Disease can be prevented with PGD.
PGS allows us to identify and separate the chromosomally normal embryos from the abnormal embryos so that only normal embryos are transferred into the woman’s uterus.
Most couples who choose PGS have one of the following conditions: recurrent miscarriages, maternal age over 38, prior unexplained IVF failures, conception of a chromosomally abnormal child or fetus, heritable medical condition in the patient or prior child (such as cystic fibrosis), or two or more children of the same gender (sex selection for family balancing).
Using PGS to select the best embryos appears to be superior to traditional methods of embryo selection. With PGS, the laboratory can detect more than 90% of abnormal embryos and thus avoid the transfer of abnormal embryos.
Once the pregnancy test is positive, couples can be more optimistic that they will experience the birth of a genetically normal child. Although single digit miscarriage rates do occur after PGS, miscarriage rates will likely decrease and implantation rates will likely increase as the technology associated with PGS continues to grow. PGS and other technologies will also help us to reach the goal of transferring a single embryo and therefore greatly increasing the probability of a singleton pregnancy.