A light micrograph of a section of fetal ovary shows primordial follicles (light pink ovals) with oocytes (dark pink spots) that have already begun to mature into fertilizable eggs. But the process won’t be complete for decades, during which time mistakes in chromosome division can occur.© TISSUEPIX/SCIENCE SOURCE
Up to a quarter of pregnancies are not carried to term; oftentimes an embryo is aborted by the body before a woman even knows she’s pregnant. The most common cause of miscarriage is egg aneuploidy—the oocyte contains too many or too few chromosomes. Aneuploidy is thus the leading genetic cause of infertility, and those embryos that are not miscarried can result in children with developmental disorders, such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Turner syndrome (monosomy X).
The life of an oocyte begins during female fetal development but does not finish for decades, providing multiple windows of opportunity for problems that compromise egg quality.
For more than 80 years, the scientific community has known that the incidence of Down syndrome births ...
