Evaluation of germ cells development in gonads of human fetuses and newborns

Germ cells development at particular stages of gonad differentiation during the period of fetal intrauterine life were investigated. The study was performed on 101 ovaries obtained from 76 fetuses and neonates. The earliest ovary obtained was from a 12-week old fetus, the oldest one was from a full-term fetus. The examination of germ cells was based on the analysis of the morphology and enzymatic activity. The morphology of the cells was studied by the use of light and electromicroscopy. In germ cells development three forms were distinguished: gonocytes, oogonia and oocytes. Gonocytes were observed in all the ovaries analyzed. They were found mostly among cells covering the gonad. Basing on the difference in their size, shape of nucleus and cytoplasm gonocytes were divided into older ones and younger ones. In the ovaries of fetuses, as early as the 14th week of the intrauterine life, oogonia were observed. Their fairly regular shape, abundance of cytoplasm and large nucleus, often with nucleolus, made their observation possible even in light microscopy. In the cytoplasm of regularly differentiating oogonia organelles were more numerous than in gonocytes. Oocytes constituted a more differentiated form of germ cells. In comparison to the cells surrounding them, they had a larger size, were rounded in shape and had a centrally located nucleus. In the cytoplasm separated into the surrounding space was observed. In a large number of different germ cells signs of degeneration were found. The study has confirmed that irrespective of the duration of pregnancy, all forms of germ cells are present in the fetal ovaries and that the differentiation continues throughout the whole period of intrauterine life.