Why can defects during blastogenesis affect several parts of the body?

Defects during blastogenesis—the first 28 days of development—often affect multiple parts of the body because this period is when the basic body plan and domains of gene expression are established.1

Several factors contribute to the severity and widespread nature of these defects:

• Small Embryonic Size: The early embryo is very small, meaning that even minor disturbances can impact a large proportion of the developing structure.1
• Proximity of Rudiments: The organ rudiments are in close proximity to one another, increasing the likelihood that a single disruption will affect multiple developing systems.1
• Interdependence: Early development is highly integrated and interdependent; because the developmental fate of all parts of the embryo is being determined simultaneously, a failure in one area can have cascading effects on others.1

Consequently, malformations occurring during this stage are typically severe and frequently lethal, often resulting in conditions such as gross brain anomalies, heart defects, or limb absence. This contrasts with organogenesis, where defects tend to be milder and more localized to single parts of the body.12