Chromosomal Abnormality

Humans normally have 46 chromosomes in each cell. Chromosomal abnormalities include aneuploidy (wrong number, such as trisomy 21/Down syndrome), deletions, duplications, and translocations. In embryos, aneuploidy is the leading cause of implantation failure and miscarriage.

The rate of chromosomal errors in embryos rises steeply with maternal age: roughly 25% at age 30 and over 60% at age 40. Preimplantation genetic testing for aneuploidy (PGT-A) screens IVF embryos before transfer to identify euploid (chromosomally normal) embryos, with the goal of reducing miscarriage rates and improving live birth rates per transfer.