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A systematic analysis of the relation between 2 parameters of developmental stage — clinically assessed embryonic age and growth — was made for 90 human embryos at Carnegie stages 7–13 from healthy pregnancies.
The data showed remarkable individual variation in the relation between age and developmental stage of embryos at stages 11–13. It appears that the mean age for these stages in our specimens was a few days greater than the corresponding age in the currently cited standards, although a definite conclusion must await further studies.
The relation between body length and developmental stages in our embryos was not different from the corresponding standards presented by previous investigators. The relation of the number of somites to developmental stage and greatest length in 13 embryos at stages 9–11 was approximately in accord with that reported for several corresponding embryos by other investigators.
The oldest age for embryos at each stage in our data may have practical use in denying a causal relation between the exposure of pregnant women to an exogenous agent at such a stage and the subsequent appearance of specific malformations in their progeny.

Variabilities in prenatal development of orofacial system

Anat Anz. 1991;172(2):97-107.

Tanaka O.

Abstract

Reliable information on embryonic and fetal development of the human oro-facial system is meager. Much of the data available at present is not entirely reliable, because it was derived from a small number of specimens. An embryological approach with human materials is important for establishing a normal standard of development including individual variabilities as well as clarifying the embryogenesis and etiology of defective development (Nishimura et al. 1977). It is important in human craniofacial embryology to know the variabilities, that is, individual differences in developmental phenomena of the oro-facial region during human prenatal life. In recent times the importance of morphologic investigations of human development has received less emphasis. Yet, without thorough knowledge of the basic facts of prenatal human development, erroneous assumptions can be made in more dynamic approaches and lead investigators astray. Knowledge of prenatal development of human orofacial structures and some of their deviations will therefore be welcomed by many basic scientists and clinicians in the field of facial clefts and other craniofacial malformations. The author was engaged in the collection and systematic study of human embryos and fetuses with Dr. Hideo Nishimura, Emeritus Professor of Kyoto University, Kyoto, Japan, and has been studying the normal and abnormal development during prenatal life. Several results obtained from the study of a large number of specimens are presented laying stress on the orofacial development.

PMID 2048747