Background and aims: The diagnosis of human fetal age is usually estimated based on the measurement of crown-rump length or crown-heel length and the weight of the fetus. However, this estimate is not totally accurate and sometimes is necessary to combine other data to determine the fetal age. An analysis of the normal embryological development of the kidney may assist in this determination. The histology of this process, although well described, lacks photographic documentation. We intend to fill this gap by providing histologists and pathologists, especially inexperienced ones, with information about the staging of the renal development through microphotography. The objective of the present study was to achieve greater accuracy for the diagnosis of human fetal age through the proposed classification and the photographic documentation presented. Material and methods: Normal embryological development of the human kidney was studied by light microscopy. The fetal period from 6 to 40 weeks of gestation was observed according the stage of maturity of glomeruli and tubules; localization of glomeruli, occurrence of nephrogenic tissue and cortico-medullary differentiation. At least 5 different exams were observed from each week of development. Two hundred four exams were analyzed in the whole study. The histological characteristics were quantified and the process was documented by microphotography. Results and final considerations: The fetal development of the kidney was divided into 8 stages, which was documented through microphotography. Nephron structural formation occurred until the 34th week of prenatal development. From the 35th week on, tubules and glomeruli continued to mature without the formation of new nephrons. The proposed classification intends to improve the accuracy of the fetal age diagnosis.
Human fetal age; Fetal kidney; Staging of nephrogenesis
