Why are there only three autosomal trisomic condotions where a fetus will survive birth?

Only three autosomal trisomic conditions—trisomy 13 (Patau syndrome), trisomy 18 (Edwards syndrome), and trisomy 21 (Down syndrome)—result in live births due to the specific genetic and developmental impacts of these chromosomal abnormalities. Most other trisomies lead to severe developmental issues that are incompatible with life, causing miscarriage early in pregnancy. The three conditions that can survive to birth typically involve less critical chromosomes that allow for some degree of viability, though often with significant health challenges. The complexity of human development and the role of specific genes on these chromosomes also influence the survivability of these trisomies.