During the first trimester, which lasts up to 10 weeks, all major body ... major damage or deformity. At eight weeks, when most organs have formed, the embryo is called a fetus.

An embryo becomes a fetus at 10 weeks of pregnancy, but that fetus is unlikely to survive outside of a pregnant person until about 23 weeks gestation, Brandi said. The gestational sac is a thin ...

Model used to create a cellular 'hologram' of a mouse embryo could be used to visualize development in any species.