Position of follicles in normal human ovary during definitive histogenesis

Follicular growth in the mammalian ovary follows a geographically determined pattern, but no exhaustive data about their spatial localization in the cortex of human ovary exists.

The aim of this study is to assess the spatial position of the follicles during human ovarian definitive histogenesis using morphometric methods.

Ovaries removed from four fetuses, five newborns and one 8-month-old child with 46,XX karyotype was used.

The position of the different follicle categories (primordial, primary, secondary and antral) was estimated as percentage distance of the centroid of the follicle from the cortico-medullary boundary.

In normal ovaries, during definitive histogenesis, the primordial follicles progressively occupy more peripheral parts of the cortex (on average, 41% of cortical length at 20 weeks of fetal development, 53% at birth, 68% at 8 postnatal months). Primary follicles were crowded in the inner part of the cortex (newborn: 30-40% of cortical length; 8 months: 52% of cortical length). Secondary and antral follicles were sampled in all neonatal specimens and in the 8-month old specimen; they were grouped next to the cortico-medullary boundary.

Ovarian development corresponded to a migration of the maximum crowding of follicles from a position next to the medulla towards a more peripheral location. The control of the primordial follicle assembly, recruitment and development are coordinated by locally produced paracrine factors. The action of these factors seems to follow a negative gradient from the cortex toward the medulla.