Staging and Ageing of Mammalian Embryos and Fetuses

Abstract

The objective of this study was to elaborate a method of estimating the age of embryos and fetuses of mammals of unknown ontogenetic age, applicable to both altricial and precocial mammals showing different duration of intrauterine development. The method consists of two steps: First, the embryo or fetus under study has to be "staged". It is measured, weighed and classified according to the characteristics given below, in one of the 13 comparable ontogenetic stages. The second step is "ageing": the staged embryo is placed in a point on the regression curve of the respective developmental stage that corresponds to the·duration of intrauterine development. The characteristics of the comparable developmental stages, the regression curves and the way in which they are calculated are presented. This method makes it possible to estimate the age of mammalian embryos and fetuses of unknown ontogenetic age, even of those already sectioned in histological series. In this way it is also possible to estimate the rates of morphogenetic events, the growth rate of the whole embryo or of its individual parts and/or organs. Ageing, embryos, fetuses, comparable developmental stages, mammals, staging, regression age curves