PREIMPLANTATION GENETIC TESTING
WHAT IS PREIMPLANTATION GENETIC TESTING (PGT) AND ADVANCED EMBRYO SELECTION?
Previously known as PGD (Preimplantation Genetic Diagnosis), PGT refers to genetic testing of embryos created by IVF, to diagnose embryos affected by genetic problems. Only embryos clear from the genetic condition in question are transferred to achieve a pregnancy.
PGT requires the biopsy of an embryo with removal of several cells for testing. To ensure the removal of cells does not impair the embryo’s potential to result in a pregnancy, the biopsy is usually conducted on day 5 or day 6 of development (blastocyst biopsy) where the embryo has more than 200 cells. The area of the embryo that is sampled is the trophectoderm – destined to become the placenta.
The inner cell mass, destined to become the baby itself is untouched. Sophisticated genetic diagnostic techniques, including Polymerase Chain Reaction, Karyomapping, massively parallel gene sequencing, comparative genomic hybridization and single nucleotide polymorphism arrays are used to determine both the chromosome makeup of the embryo and whether an inherited genetic mutation (PGT-M), chromosome rearrangement (translocation, deletion or chromosome inversion, PGT-SR) or chromosomal aneuploidies (wrong total number of chromosomes) is present (PGT-A).
PGT can also be used in sex selection where a particular embryo sex is preferred for the avoidance of disease.
WHO IT’S FOR
PGT can help families at risk of having a baby with a serious or lethal genetic disease to have healthy babies.
Spontaneous chromosome abnormalities in embryos are increasingly common in women aged 35 and over.
Advanced genetic technologies can be used to screen embryos for chromosomal abnormalities, ensuring only chromosomally normal (euploid) embryos are transferred. This is thought to increase a woman’s chance of pregnancy per embryo transfer, and reduce both her time-to-conception and her risk of miscarriage.
This type of PGT is called PGT-A and is not eligible for Medicare benefits.
PRECONCEPTION GENETIC SCREENING
Genetic carrier screening refers to screening for the presence of “silent” (recessive) genes in two parents, that, if inherited together, could result in a baby suffering from a severe disease (e.g. cystic fibrosis). Our doctors at Women’s Health Melbourne recommend that all couples consider undertaking genetic carrier screening pre-conception.
You can choose to screen yourself and your partner for a limited number of common genetic conditions (cystic fibrosis, spinal muscular atrophy and fragile X) or opt for a more comprehensive expanded screening option including hundreds of conditions in parallel.