[Histological study of the fetal kidneys. Development of the nephrons according to gestational weeks]

Despite recent advance of prenatal ultrasonography leading to an increase in the detection of various fetal urological abnormalities, a lot a unresolved problems exist surrounding their diagnosis and management. It is unclear whether an antenatal intervention helps to preserve the renal function, because little has been known about the nephrogenesis of the human fetal kidney associated with congenital obstruction. To find the normal development of the kidney, we studied the fetal kidneys in relation to the gestational weeks. Of all fetuses autopsied in the Department of Pathology of our Institute from 1982 to 1992, 87 kidneys from 60 fetuses which showed no abnormalities of the urinary tracts on macroscopic inspections were reviewed. Microscopic examination was done to define the radial glomerular count (RGC) and glomerular size according to gestational weeks. Nephrogenic zone was observed in all kidneys before 34 weeks of gestation, and disappeared in all kidneys after 37 weeks. The RGC increased steadily with gestational weeks, and gradually reached a plateau of around 12 counts at about 36 weeks. The RGC was not influenced by the intrauterine fetal growth. The glomeruli were arranged in the uniform fashion on the medullary ray with the smallest in the most superficial cortex and the largest in the juxtamedullary zone. The superficial glomeruli remained at the surprisingly same size up to birth. Juxtamedullary glomeruli showed no significant differences before birth, either. Based on the present studies to know the normal standard of renal development, pathological changes are possible to define. It was thought that an understanding of the morphological characteristics of fetal kidneys would give clues to elucidate pathogenesis of abnormal kidneys.