preembryonische

Preembryonische is a term used in developmental biology to refer to the early stage of development that occurs after fertilization but before the embryonic body plan is established. In humans and many mammals, this pre-embryonische period lasts roughly the first two weeks of development and culminates with implantation into the uterine lining and the formation of the bilaminar germ disc.

During this phase, fertilization forms a zygote that undergoes cleavage, producing successive generations of cells without growth. These divisions yield 2-cell, 4-cell, and 8-cell stages, then a morula, and finally a blastocyst. The blastocyst contains an outer trophoblast layer, an inner cell mass, and a fluid-filled cavity. Implantation into the endometrium follows, typically about 6 to 10 days after fertilization in humans. The early extraembryonic membranes and supporting structures begin to form during this period.

Definition and boundaries: The preembryonische stage ends when gastrulation begins, marking the transition to the embryonic period. The term is often used together with preimplantation to describe events prior to implantation. Differences in timing and morphology occur across species, but the general sequence—zygote, cleavage, morula, blastocyst, implantation—is broadly conserved. Clinically, disruptions during the preembryonische phase can lead to early pregnancy loss, making this period a focus of reproductive biology and assisted reproduction research.