A morphometric approach to the study of human ovarian organogenesis

This study deals with the morphometric approach used to describe the quantitative characteristics of human ovaries during their final histogenesis. Fixed ovaries ranging from the 20th fetal week to the 8th postnatal month were used. They were measured using a high precision caliper, were embedded in toto in epoxide resin, and systematically cut (1 microm-thick sections) orthogonal to the major axis of the organ. The surface areas were automatically measured, at low magnification, and ovarian volume was calculated using the Cavalieri method. The volume fractions of ovarian medulla, primitive cortical tissue, primordial, primary, secondary and Graafian follicles, and stroma were calculated by differential point counting at higher magnification. At the same magnification, the position of the different follicle categories in the cortex was estimated as percentage distance of the follicle from the cortico-medullary boundary. The number in unit cortex volume of the oocyte nuclei in primordial and primary follicles were derived by diameter analysis according to the Schwartz-Saltykov method, and the total follicle number for each ovary was obtained. The diameter of nuclear, cellular and follicular profiles of primary and primordial follicles in sections was also measured. Ovarian volume was about 30 mm3 at 20 fetal weeks and 287 mm3 at the 8th postnatal month, with a 9.5-fold increment. Irrespective of age, the cortex occupied most of the organs, ranging from 90% at 20 prenatal weeks (about 27 mm3) to 85% at 8 postnatal months (about 245 mm3). In the cortex, the interstitium or stroma intermingled with the germinal component: primitive cortical tissue was found in all ovaries, and its absolute volume remained unmodified between the 20th fetal week and birth. In the analyzed fetal stages, the total number of primordial follicles had its largest modification, with a 1.3-fold increment between the 20th-25th fetal weeks. Hereafter, the number increased at a slower rate (about 1.2 times between the 25th week and birth, 1.1 times between birth and the 8th postnatal month). The largest absolute volume of primordial follicles was found at birth. Follicular, oocyte and nuclear diameters increased during the intrauterine life, while after birth their dimensions did not modify further. Conversely, their spatial position in the cortex modified even after birth. In the 8-month old child nearly all germinal cells were comprised into follicles in different degrees of development, and the primitive cortical tissue was exhausted. A three-dimensional geometrical model of human ovary has also been elaborated to define the spatial organization of ovarian germinal and somatic components, and to allow the comparison of the present data to the "in-vivo" volumetric assessments.