First Trimester Embryology: An Overview

Early human embryonic development is a complex and continuous process. In the first trimester, the embryo rapidly develops from a multicellular group of cells into a multilayered structure called the gastrula, which contains a trilaminar disc, from which all future organ systems will develop. Each organ system undergoes their own unique developmental process. Any deviation from this process results in congenital anomalies, which can often be identified by ultrasound as early as the first trimester. To understand the etiology of congenital anomalies that are identified throughout pregnancy, it is essential that one gains a basic understanding of the embryo development as well as the complex signaling and migration processes involved in its development.