The Carnegie system describes the different stages of maturation of embryos. The stages are numbered from 1 to 23 based on the morphology of the embryo.

The parameters that are used in staging are the body length, external body shape and degree of development of internal organs.

Staging is not dependent on the chronological age or the size of the embryo.

The differentiation is arbitrarily based on the maturity of the physical features. This system is widely used as reference during ultrasonographic assessment during pregnancy.