Histological assessment of gestational age in human embryos and fetuses.

A light microscopic study performed on 760 human fetuses allows us to define several stages in their visceral development and to relate these to gestational age. The histological examination of most viscera, such as the central nervous system, is useless when the tissue preservation is poor. Nevertheless, three organs may still be studied in macerated fetuses: the lungs (where different glandular, canalar, and alveolar stages of development are evident), the kidneys (where the respective numbers of rows of primitive glomeruli and of generations of mature glomeruli vary after week 22), and the adrenal glands (where neuroblastic nests are normally found between weeks 7 and 26 of gestation). It is important to compare the degree of histological maturation with the clinical, macroscopic, and radiologic data in order to define the profile of maturation proper to each human fetus.