PURPOSE: to determine the variation of the number of ovarian follicles during fetal life. METHODS: twelve ovaries donated for research were included in our study, nine from fetuses and three from newborn babies who died in the first hour after being delivered with 39 weeks of pregnancy. Fetal age was confirmed both by the last menstrual period of the woman and by ultrasonography. Ovaries were fixed in formaldehyde, included in paraffin and serially sliced at 7 mm. At every 50 cuts, the obtained material was haematoxilin-eosin stained and evaluated with an optical microscope (400 X). The follicles were counted in ten different regions of the ovarian cortex, each region with an area of 625 mm². The presence of a nucleus was considered the parameter for counting. Follicular density, per 1 mm³ was calculated using the formula Nt=(No x St x t)/do, where Nt is the number of follicles; No is the mean number of follicles in 1 mm²; St is the total number of slices in 1 mm³; t is the slice thickness and do is the nuclei mean diameter. RESULTS: the gestational age of fetuses ranged from 24 to 39 weeks. The number of follicles per 0.25 mm² ranged from 10.9 ± 4.8 in a newborn to 34.7 ± 10.6 in another newborn. Among the fetuses, the least value was obtained in a 36 week-old fetus (11.1 ± 6.2) and the highest in a 28 week-old fetus (25.3 ± 9.6). The total number of slices per ovary ranged from six to 13, corresponding to follicles counted in areas from 15 to 32.5 mm². The total number of follicles ranged from 500,000 at the age of 22 weeks to > 1,000,000 at the age of 39 weeks. CONCLUSIONS: our results demonstrate different (increasing) densities of ovarian follicles along the gestational period, providing more knowledge about this still not well-known subject.
Follicular density; Ovary; Fetus; Ovarian follicle
