MORPHOLOGICAL AND MOLECULAR CHARACTERISTICS OF LIVING HUMAN FETUSES BETWEEN CARNEGIE STAGE-7 AND STAGE-23 - DEVELOPMENTAL STAGES IN THE POSTIMPLANTATION EMBRYO

Determination of embryonic age groups or stages has been based on the Carnegie Institute collection started in 1887. Improved technology has enabled the building of a new collection of embryos of <9 weeks gesta tion; these were then used to compare with the original Carnegie colle ction. The results suggest that in providing definitive stages that ar e rigidly bound by developmental events, limitations are placed on cat egorizing the embryo. Allocation of embryos to a specific stage can as sist in identifying post-ovulatory age but overlaps between stages cou ld lead to classification into an incorrect stage.