A morphometric approach to the study of human ovarian organogenesis.

This study deals with the morphometric approach used to describe the quanti tative characteristics of human ovaries during their final histogenesis. Fi xed ovaries ranging from the 20(th) fetal meek to the 8(th) postnatal month were used. They were measured using a high precision caliper, were embedde d in tote in epoxide resin, and systematically cut (1 mu m-thick sections) orthogonal to the major axis of the organ. The surface areas were automatic ally measured, at low magnification, and ovarian volume was calculated usin g 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 magnificat ion. At the same magnification, the position of the different follicle cate gories in the cortex was estimated as percentage distance of the follicle f rom 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 als o measured. Ovarian volume was about 30 mm(3) at 20 fetal weeks and 287 mm(3) at the 8( th) postnatal month, with a 9.5-fold increment. Irrespective of age, the co rtex occupied most of the organs, ranging from 90% at 20 prenatal weeks (ab out 27 mm(3)) to 85% at 8 postnatal months (about 245 mm(3)). In the cortex , the interstitium or stroma intermingled with the germinal component: prim itive cortical tissue was found in all ovaries, and its absolute volume rem ained unmodified between the 20th fetal week and birth. In the analyzed fet al stages, the total number of primordial follicles had its largest modific ation, with a 1.3-fold increment between the 20(th)-22(th); fetal weeks. He reafter, the number increased at a slower rate (about 1.2 times between the 25(th) week and birth, 1.1 times between birth and the 8(th) postnatal mon th). The largest absolute volume of primordial follicles was found at birth . Follicular, oocyte and nuclear diameters increased during the intrauterin e life, while after birth their dimensions did not modify further. Converse ly, their spatial position in the cortex modified even after birth. In the S-month old child nearly all germinal cells were comprised into follicles i n different degrees of development, and the primitive cortical tissue was e xhausted. A three-dimensional geometrical model of human ovary has also been elaborat ed to define the spatial organization of ovarian germinal and somatic compo nents, and to allow the comparison of the present data to the "in-vivo" vol umetric assessments.