Why do defects that arise during organogenesis usually affect one body part rather than many?

Defects that arise during organogenesis typically affect a single body part because this stage of development, occurring between days 29 and 56 of human embryogenesis, involves the formation of specific, localized organ primordia rather than the broad, systemic organization of the entire embryo.12

During this period, the embryo undergoes integrated processes where specific groups of cells differentiate into distinct organs. Because these developmental pathways are highly localized and rely on specific embryonic induction—where inducing substances trigger particular paths of development in nearby tissues—a disruption at this stage is often confined to the specific organ or structure currently forming. Consequently, these defects, such as cleft palate or syndactyly (webbed fingers), are generally more limited in scope compared to abnormalities that occur during earlier stages of development, such as blastogenesis, which involve the fundamental organization of the entire organism.132