Final answer:
Aneuploidy, particularly trisomies, often leads to spontaneous miscarriages and developmental challenges. The most common trisomy within viable births is Trisomy 21, known as Down Syndrome, with increased risk associated with higher maternal age.
Step-by-step explanation:
An individual with an error in chromosome number is described as aneuploid, which can result in pregnancy loss. While specific percentages of such pregnancy losses due to aneuploidy are not provided, it's noted that the majority of autosomal aneuploidies fail to develop to birth. For instance, the most common trisomy in humans, which is not specified, results in a high rate of spontaneous miscarriages in the first trimester. However, when it comes to viable births, Trisomy 21 is the most prevalent, associated with Down Syndrome, and its incidence increases with maternal age.