JCJC Human Growth and Development Practice Test

During prenatal development, organ formation happens in the embryonic period, which runs roughly from three to eight weeks after conception. This is when organogenesis occurs—the major organs and body structures begin to take shape, so the period lasts about six weeks and sets up the basic body plan. Because so many systems are forming, this stage is when the embryo is especially vulnerable to disruptions that can lead to congenital defects.

In contrast, the germinal period encompasses the first two weeks after conception and focuses on cell division and implantation, not organ formation. The fetal period begins after organ formation has started and centers on growth and maturation of already formed organs. The neonatal period refers to the weeks after birth, not prenatal development.